Should have been done this way to start with, but I failed to notice
This way we avoid some pointless initialization, and better contains the
variable to exist in the scope where it is really used.
Reviewed-by: Michaël Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/202204191345.qerjy3kxi3eb@alvherre.pgsql
There's no reason to keep a separate local variable when we have a place
for it elsewhere. This allows to simplify some code.
Reviewed-by: Michaël Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/202204191345.qerjy3kxi3eb@alvherre.pgsql
Previously, the output of EXPLAIN (BUFFERS) option showed only the I/O
timing spent reading and writing shared and local buffers. This commit
adds on top of that the I/O timing for temporary buffers in the output
of EXPLAIN (for spilled external sorts, hashes, materialization. etc).
This can be helpful for users in cases where the I/O related to
temporary buffers is the bottleneck.
Like its cousin, this information is available only when track_io_timing
is enabled. Playing the patch, this is showing an extra overhead of up
to 1% even when using gettimeofday() as implementation for interval
timings, which is slightly within the usual range noise still that's
measurable.
Author: Masahiko Sawada
Reviewed-by: Georgios Kokolatos, Melanie Plageman, Julien Rouhaud,
Ranier Vilela
Discussion: https://postgr.es/m/CAD21AoAJgotTeP83p6HiAGDhs_9Fw9pZ2J=_tYTsiO5Ob-V5GQ@mail.gmail.com
Window functions such as row_number() always return a value higher than
the previously returned value for tuples in any given window partition.
Traditionally queries such as;
SELECT * FROM (
SELECT *, row_number() over (order by c) rn
FROM t
) t WHERE rn <= 10;
were executed fairly inefficiently. Neither the query planner nor the
executor knew that once rn made it to 11 that nothing further would match
the outer query's WHERE clause. It would blindly continue until all
tuples were exhausted from the subquery.
Here we implement means to make the above execute more efficiently.
This is done by way of adding a pg_proc.prosupport function to various of
the built-in window functions and adding supporting code to allow the
support function to inform the planner if the window function is
monotonically increasing, monotonically decreasing, both or neither. The
planner is then able to make use of that information and possibly allow
the executor to short-circuit execution by way of adding a "run condition"
to the WindowAgg to allow it to determine if some of its execution work
can be skipped.
This "run condition" is not like a normal filter. These run conditions
are only built using quals comparing values to monotonic window functions.
For monotonic increasing functions, quals making use of the btree
operators for <, <= and = can be used (assuming the window function column
is on the left). You can see here that once such a condition becomes false
that a monotonic increasing function could never make it subsequently true
again. For monotonically decreasing functions the >, >= and = btree
operators for the given type can be used for run conditions.
The best-case situation for this is when there is a single WindowAgg node
without a PARTITION BY clause. Here when the run condition becomes false
the WindowAgg node can simply return NULL. No more tuples will ever match
the run condition. It's a little more complex when there is a PARTITION
BY clause. In this case, we cannot return NULL as we must still process
other partitions. To speed this case up we pull tuples from the outer
plan to check if they're from the same partition and simply discard them
if they are. When we find a tuple belonging to another partition we start
processing as normal again until the run condition becomes false or we run
out of tuples to process.
When there are multiple WindowAgg nodes to evaluate then this complicates
the situation. For intermediate WindowAggs we must ensure we always
return all tuples to the calling node. Any filtering done could lead to
incorrect results in WindowAgg nodes above. For all intermediate nodes,
we can still save some work when the run condition becomes false. We've
no need to evaluate the WindowFuncs anymore. Other WindowAgg nodes cannot
reference the value of these and these tuples will not appear in the final
result anyway. The savings here are small in comparison to what can be
saved in the top-level WingowAgg, but still worthwhile.
Intermediate WindowAgg nodes never filter out tuples, but here we change
WindowAgg so that the top-level WindowAgg filters out tuples that don't
match the intermediate WindowAgg node's run condition. Such filters
appear in the "Filter" clause in EXPLAIN for the top-level WindowAgg node.
Here we add prosupport functions to allow the above to work for;
row_number(), rank(), dense_rank(), count(*) and count(expr). It appears
technically possible to do the same for min() and max(), however, it seems
unlikely to be useful enough, so that's not done here.
Bump catversion
Author: David Rowley
Reviewed-by: Andy Fan, Zhihong Yu
Discussion: https://postgr.es/m/CAApHDvqvp3At8++yF8ij06sdcoo1S_b2YoaT9D4Nf+MObzsrLQ@mail.gmail.com
Modify the subroutines called by RI trigger functions that want to check
if a given referenced value exists in the referenced relation to simply
scan the foreign key constraint's unique index, instead of using SPI to
execute
SELECT 1 FROM referenced_relation WHERE ref_key = $1
This saves a lot of work, especially when inserting into or updating a
referencing relation.
This rewrite allows to fix a PK row visibility bug caused by a partition
descriptor hack which requires ActiveSnapshot to be set to come up with
the correct set of partitions for the RI query running under REPEATABLE
READ isolation. We now set that snapshot indepedently of the snapshot
to be used by the PK index scan, so the two no longer interfere. The
buggy output in src/test/isolation/expected/fk-snapshot.out of the
relevant test case added by commit 00cb86e75d has been corrected.
(The bug still exists in branch 14, however, but this fix is too
invasive to backpatch.)
Author: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Corey Huinker <corey.huinker@gmail.com>
Reviewed-by: Li Japin <japinli@hotmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>
Discussion: https://postgr.es/m/CA+HiwqGkfJfYdeq5vHPh6eqPKjSbfpDDY+j-kXYFePQedtSLeg@mail.gmail.com
* Move the execution pruning initialization steps that are common
between both ExecInitAppend() and ExecInitMergeAppend() into a new
function ExecInitPartitionPruning() defined in execPartition.c.
Those steps include creation of a PartitionPruneState to be used for
all instances of pruning and determining the minimal set of child
subplans that need to be initialized by performing initial pruning if
needed, and finally adjusting the subplan_map arrays in the
PartitionPruneState to reflect the new set of subplans remaining
after initial pruning if it was indeed performed.
ExecCreatePartitionPruneState() is no longer exported out of
execPartition.c and has been renamed to CreatePartitionPruneState()
as a local sub-routine of ExecInitPartitionPruning().
* Likewise, ExecFindInitialMatchingSubPlans() that was in charge of
performing initial pruning no longer needs to be exported. In fact,
since it would now have the same body as the more generally named
ExecFindMatchingSubPlans(), except differing in the value of
initial_prune passed to the common subroutine
find_matching_subplans_recurse(), it seems better to remove it and add
an initial_prune argument to ExecFindMatchingSubPlans().
* Add an ExprContext field to PartitionPruneContext to remove the
implicit assumption in the runtime pruning code that the ExprContext to
use to compute pruning expressions that need one can always rely on the
PlanState providing it. A future patch will allow runtime pruning (at
least the initial pruning steps) to be performed without the
corresponding PlanState yet having been created, so this will help.
Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CA+HiwqEYCpEqh2LMDOp9mT+4-QoVe8HgFMKBjntEMCTZLpcCCA@mail.gmail.com
This feature allows jsonb data to be treated as a table and thus used in
a FROM clause like other tabular data. Data can be selected from the
jsonb using jsonpath expressions, and hoisted out of nested structures
in the jsonb to form multiple rows, more or less like an outer join.
Nikita Glukhov
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zhihong Yu (whose
name I previously misspelled), Himanshu Upadhyaya, Daniel Gustafsson,
Justin Pryzby.
Discussion: https://postgr.es/m/7e2cb85d-24cf-4abb-30a5-1a33715959bd@postgrespro.ru
The general usage pattern when we store tuples in tuplesort.c is that
we store a series of tuples one by one then either perform a sort or spill
them to disk. In the common case, there is no pfreeing of already stored
tuples. For the common case since we do not individually pfree tuples, we
have very little need for aset.c memory allocation behavior which
maintains freelists and always rounds allocation sizes up to the next
power of 2 size.
Here we conditionally use generation.c contexts for storing tuples in
tuplesort.c when the sort will never be bounded. Unfortunately, the
memory context to store tuples is already created by the time any calls
would be made to tuplesort_set_bound(), so here we add a new sort option
that allows callers to specify if they're going to need a bounded sort or
not. We'll use a standard aset.c allocator when this sort option is not
set.
Extension authors must ensure that the TUPLESORT_ALLOWBOUNDED flag is
used when calling tuplesort_begin_* for any sorts that make a call to
tuplesort_set_bound().
Author: David Rowley
Reviewed-by: Andy Fan
Discussion: https://postgr.es/m/CAApHDvoH4ASzsAOyHcxkuY01Qf++8JJ0paw+03dk+W25tQEcNQ@mail.gmail.com
This replaces the bool flag for randomAccess. An upcoming patch requires
adding another option, so instead of breaking the API for that, then
breaking it again one day if we add more options, let's just break it
once. Any boolean options we add in the future will just make use of an
unused bit in the flags.
Any extensions making use of tuplesorts will need to update their code
to pass TUPLESORT_RANDOMACCESS instead of true for randomAccess.
TUPLESORT_NONE can be used for a set of empty options.
Author: David Rowley
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/CAApHDvoH4ASzsAOyHcxkuY01Qf%2B%2B8JJ0paw%2B03dk%2BW25tQEcNQ%40mail.gmail.com
This Patch introduces three SQL standard JSON functions:
JSON() (incorrectly mentioned in my commit message for f4fb45d15c)
JSON_SCALAR()
JSON_SERIALIZE()
JSON() produces json values from text, bytea, json or jsonb values, and
has facilitites for handling duplicate keys.
JSON_SCALAR() produces a json value from any scalar sql value, including
json and jsonb.
JSON_SERIALIZE() produces text or bytea from input which containis or
represents json or jsonb;
For the most part these functions don't add any significant new
capabilities, but they will be of use to users wanting standard
compliant JSON handling.
Nikita Glukhov
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
This introduces the SQL/JSON functions for querying JSON data using
jsonpath expressions. The functions are:
JSON_EXISTS()
JSON_QUERY()
JSON_VALUE()
All of these functions only operate on jsonb. The workaround for now is
to cast the argument to jsonb.
JSON_EXISTS() tests if the jsonpath expression applied to the jsonb
value yields any values. JSON_VALUE() must return a single value, and an
error occurs if it tries to return multiple values. JSON_QUERY() must
return a json object or array, and there are various WRAPPER options for
handling scalar or multi-value results. Both these functions have
options for handling EMPTY and ERROR conditions.
Nikita Glukhov
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
This patch intrdocuces the SQL standard IS JSON predicate. It operates
on text and bytea values representing JSON as well as on the json and
jsonb types. Each test has an IS and IS NOT variant. The tests are:
IS JSON [VALUE]
IS JSON ARRAY
IS JSON OBJECT
IS JSON SCALAR
IS JSON WITH | WITHOUT UNIQUE KEYS
These are mostly self-explanatory, but note that IS JSON WITHOUT UNIQUE
KEYS is true whenever IS JSON is true, and IS JSON WITH UNIQUE KEYS is
true whenever IS JSON is true except it IS JSON OBJECT is true and there
are duplicate keys (which is never the case when applied to jsonb values).
Nikita Glukhov
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
MERGE performs actions that modify rows in the target table using a
source table or query. MERGE provides a single SQL statement that can
conditionally INSERT/UPDATE/DELETE rows -- a task that would otherwise
require multiple PL statements. For example,
MERGE INTO target AS t
USING source AS s
ON t.tid = s.sid
WHEN MATCHED AND t.balance > s.delta THEN
UPDATE SET balance = t.balance - s.delta
WHEN MATCHED THEN
DELETE
WHEN NOT MATCHED AND s.delta > 0 THEN
INSERT VALUES (s.sid, s.delta)
WHEN NOT MATCHED THEN
DO NOTHING;
MERGE works with regular tables, partitioned tables and inheritance
hierarchies, including column and row security enforcement, as well as
support for row and statement triggers and transition tables therein.
MERGE is optimized for OLTP and is parameterizable, though also useful
for large scale ETL/ELT. MERGE is not intended to be used in preference
to existing single SQL commands for INSERT, UPDATE or DELETE since there
is some overhead. MERGE can be used from PL/pgSQL.
MERGE does not support targetting updatable views or foreign tables, and
RETURNING clauses are not allowed either. These limitations are likely
fixable with sufficient effort. Rewrite rules are also not supported,
but it's not clear that we'd want to support them.
Author: Pavan Deolasee <pavan.deolasee@gmail.com>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Simon Riggs <simon.riggs@enterprisedb.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Andres Freund <andres@anarazel.de> (earlier versions)
Reviewed-by: Peter Geoghegan <pg@bowt.ie> (earlier versions)
Reviewed-by: Robert Haas <robertmhaas@gmail.com> (earlier versions)
Reviewed-by: Japin Li <japinli@hotmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>
Discussion: https://postgr.es/m/CANP8+jKitBSrB7oTgT9CY2i1ObfOt36z0XMraQc+Xrz8QB0nXA@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzkJdBuxj9PO=2QaO9-3h3xGbQPZ34kJH=HukRekwM-GZg@mail.gmail.com
Discussion: https://postgr.es/m/20201231134736.GA25392@alvherre.pgsql
This patch introduces the SQL/JSON standard constructors for JSON:
JSON()
JSON_ARRAY()
JSON_ARRAYAGG()
JSON_OBJECT()
JSON_OBJECTAGG()
For the most part these functions provide facilities that mimic
existing json/jsonb functions. However, they also offer some useful
additional functionality. In addition to text input, the JSON() function
accepts bytea input, which it will decode and constuct a json value from.
The other functions provide useful options for handling duplicate keys
and null values.
This series of patches will be followed by a consolidated documentation
patch.
Nikita Glukhov
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
This introduces some of the building blocks used by the SQL/JSON
constructor and query functions. Specifically, it provides node
executor and grammar support for the FORMAT JSON [ENCODING foo]
clause, and values decorated with it, and for the RETURNING clause.
The following SQL/JSON patches will leverage these.
Nikita Glukhov (who probably deserves an award for perseverance).
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
This allows specifying an optional column list when adding a table to
logical replication. The column list may be specified after the table
name, enclosed in parentheses. Columns not included in this list are not
sent to the subscriber, allowing the schema on the subscriber to be a
subset of the publisher schema.
For UPDATE/DELETE publications, the column list needs to cover all
REPLICA IDENTITY columns. For INSERT publications, the column list is
arbitrary and may omit some REPLICA IDENTITY columns. Furthermore, if
the table uses REPLICA IDENTITY FULL, column list is not allowed.
The column list can contain only simple column references. Complex
expressions, function calls etc. are not allowed. This restriction could
be relaxed in the future.
During the initial table synchronization, only columns included in the
column list are copied to the subscriber. If the subscription has
several publications, containing the same table with different column
lists, columns specified in any of the lists will be copied.
This means all columns are replicated if the table has no column list
at all (which is treated as column list with all columns), or when of
the publications is defined as FOR ALL TABLES (possibly IN SCHEMA that
matches the schema of the table).
For partitioned tables, publish_via_partition_root determines whether
the column list for the root or the leaf relation will be used. If the
parameter is 'false' (the default), the list defined for the leaf
relation is used. Otherwise, the column list for the root partition
will be used.
Psql commands \dRp+ and \d <table-name> now display any column lists.
Author: Tomas Vondra, Alvaro Herrera, Rahila Syed
Reviewed-by: Peter Eisentraut, Alvaro Herrera, Vignesh C, Ibrar Ahmed,
Amit Kapila, Hou zj, Peter Smith, Wang wei, Tang, Shi yu
Discussion: https://postgr.es/m/CAH2L28vddB_NFdRVpuyRBJEBWjz4BSyTB=_ektNRH8NJ1jf95g@mail.gmail.com
This commit adds support for decoding of sequences to the built-in
replication (the infrastructure was added by commit 0da92dc530).
The syntax and behavior mostly mimics handling of tables, i.e. a
publication may be defined as FOR ALL SEQUENCES (replicating all
sequences in a database), FOR ALL SEQUENCES IN SCHEMA (replicating
all sequences in a particular schema) or individual sequences.
To publish sequence modifications, the publication has to include
'sequence' action. The protocol is extended with a new message,
describing sequence increments.
A new system view pg_publication_sequences lists all the sequences
added to a publication, both directly and indirectly. Various psql
commands (\d and \dRp) are improved to also display publications
including a given sequence, or sequences included in a publication.
Author: Tomas Vondra, Cary Huang
Reviewed-by: Peter Eisentraut, Amit Kapila, Hannu Krosing, Andres
Freund, Petr Jelinek
Discussion: https://postgr.es/m/d045f3c2-6cfb-06d3-5540-e63c320df8bc@enterprisedb.com
Discussion: https://postgr.es/m/1710ed7e13b.cd7177461430746.3372264562543607781@highgo.ca
This introduces some of the building blocks used by the SQL/JSON
constructor and query functions. Specifically, it provides node
executor and grammar support for the FORMAT JSON [ENCODING foo]
clause, and values decorated with it, and for the RETURNING clause.
The following SQL/JSON patches will leverage these.
Nikita Glukhov (who probably deserves an award for perseverance).
Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup. Erik Rijkers, Zihong Yu and
Himanshu Upadhyaya.
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Valgrind animal skink shows a crash in this new code. I couldn't
reproduce the problem locally, but going by blind code inspection,
initializing insert_destrel should be sufficient to fix the problem.
When an update on a partitioned table referenced in foreign key
constraints causes a row to move from one partition to another,
the fact that the move is implemented as a delete followed by an insert
on the target partition causes the foreign key triggers to have
surprising behavior. For example, a given foreign key's delete trigger
which implements the ON DELETE CASCADE clause of that key will delete
any referencing rows when triggered for that internal DELETE, although
it should not, because the referenced row is simply being moved from one
partition of the referenced root partitioned table into another, not
being deleted from it.
This commit teaches trigger.c to skip queuing such delete trigger events
on the leaf partitions in favor of an UPDATE event fired on the root
target relation. Doing so is sensible because both the old and the new
tuple "logically" belong to the root relation.
The after trigger event queuing interface now allows passing the source
and the target partitions of a particular cross-partition update when
registering the update event for the root partitioned table. Along with
the two ctids of the old and the new tuple, the after trigger event now
also stores the OIDs of those partitions. The tuples fetched from the
source and the target partitions are converted into the root table
format, if necessary, before they are passed to the trigger function.
The implementation currently has a limitation that only the foreign keys
pointing into the query's target relation are considered, not those of
its sub-partitioned partitions. That seems like a reasonable
limitation, because it sounds rare to have distinct foreign keys
pointing to sub-partitioned partitions instead of to the root table.
This misbehavior stems from commit f56f8f8da6 (which added support for
foreign keys to reference partitioned tables) not paying sufficient
attention to commit 2f17844104 (which had introduced cross-partition
updates a year earlier). Even though the former commit goes back to
Postgres 12, we're not backpatching this fix at this time for fear of
destabilizing things too much, and because there are a few ABI breaks in
it that we'd have to work around in older branches. It also depends on
commit f4566345cf, which had its own share of backpatchability issues
as well.
Author: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reported-by: Eduard Català <eduard.catala@gmail.com>
Discussion: https://postgr.es/m/CA+HiwqFvkBCmfwkQX_yBqv2Wz8ugUGiBDxum8=WvVbfU1TXaNg@mail.gmail.com
Discussion: https://postgr.es/m/CAL54xNZsLwEM1XCk5yW9EqaRzsZYHuWsHQkA2L5MOSKXAwviCQ@mail.gmail.com
In commit bf7ca1587, I had the bright idea that we could make the
result of a whole-row Var (that is, foo.*) track any column aliases
that had been applied to the FROM entry the Var refers to. However,
that's not terribly logically consistent, because now the output of
the Var is no longer of the named composite type that the Var claims
to emit. bf7ca1587 tried to handle that by changing the output
tuple values to be labeled with a blessed RECORD type, but that's
really pretty disastrous: we can wind up storing such tuples onto
disk, whereupon they're not readable by other sessions.
The only practical fix I can see is to give up on what bf7ca1587
tried to do, and say that the column names of tuples produced by
a whole-row Var are always those of the underlying named composite
type, query aliases or no. While this introduces some inconsistencies,
it removes others, so it's not that awful in the abstract. What *is*
kind of awful is to make such a behavioral change in a back-patched
bug fix. But corrupt data is worse, so back-patched it will be.
(A workaround available to anyone who's unhappy about this is to
introduce an extra level of sub-SELECT, so that the whole-row Var is
referring to the sub-SELECT's output and not to a named table type.
Then the Var is of type RECORD to begin with and there's no issue.)
Per report from Miles Delahunty. The faulty commit dates to 9.5,
so back-patch to all supported branches.
Discussion: https://postgr.es/m/2950001.1638729947@sss.pgh.pa.us
Create subroutines ExecUpdatePrologue / ExecUpdateAct /
ExecUpdateEpilogue, and similar for ExecDelete.
Introduce a new struct to be used internally in nodeModifyTable.c,
dubbed ModifyTableContext, which contains all context information needed
to perform these operations, as well as ExecInsert and others.
This allows using a different schedule and a different way of evaluating
the results of these operations, which can be exploited by a later
commit introducing support for MERGE. It also makes ExecUpdate and
ExecDelete proper shorter and (hopefully) simpler.
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Japin Li <japinli@hotmail.com>
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>
Discussion: https://postgr.es/m/202202271724.4z7xv3cf46kv@alvherre.pgsql
There are three parallel ways to call parse/analyze: with fixed
parameters, with variable parameters, and by supplying your own parser
callback. Some of the involved functions were confusingly named and
made this API structure more confusing. This patch renames some
functions to make this clearer:
parse_analyze() -> parse_analyze_fixedparams()
pg_analyze_and_rewrite() -> pg_analyze_and_rewrite_fixedparams()
(Otherwise one might think this variant doesn't accept parameters, but
in fact all three ways accept parameters.)
pg_analyze_and_rewrite_params() -> pg_analyze_and_rewrite_withcb()
(Before, and also when considering pg_analyze_and_rewrite(), one might
think this is the only way to pass parameters. Moreover, the parser
callback doesn't necessarily need to parse only parameters, it's just
one of the things it could do.)
parse_fixed_parameters() -> setup_parse_fixed_parameters()
parse_variable_parameters() -> setup_parse_variable_parameters()
(These functions don't actually do any parsing, they just set up
callbacks to use during parsing later.)
This patch also adds some const decorations to the fixed-parameters
API, so the distinction from the variable-parameters API is more
clear.
Reviewed-by: Nathan Bossart <bossartn@amazon.com>
Discussion: https://www.postgresql.org/message-id/flat/c67ce276-52b4-0239-dc0e-39875bf81840@enterprisedb.com
This is pretty queasy-making on general principles, and the more so
once you notice that CommitTransactionCommand() is actually stomping
on the values saved by _SPI_commit(). It's okay as long as the
active values didn't change during HoldPinnedPortals(); but that's
a larger assumption than I think we want to make, especially since
the fix is so simple.
Discussion: https://postgr.es/m/1533956.1645731245@sss.pgh.pa.us
SPI_commit previously left it up to the caller to recover from any error
occurring during commit. Since that's complicated and requires use of
low-level xact.c facilities, it's not too surprising that no caller got
it right. Let's move the responsibility for cleanup into spi.c. Doing
that requires redefining SPI_commit as starting a new transaction, so
that it becomes equivalent to SPI_commit_and_chain except that you get
default transaction characteristics instead of preserving the prior
transaction's characteristics. We can make this pretty transparent
API-wise by redefining SPI_start_transaction() as a no-op. Callers
that expect to do something in between might be surprised, but
available evidence is that no callers do so.
Having made that API redefinition, we can fix this mess by having
SPI_commit[_and_chain] trap errors and start a new, clean transaction
before re-throwing the error. Likewise for SPI_rollback[_and_chain].
Some cleanup is also needed in AtEOXact_SPI, which was nowhere near
smart enough to deal with SPI contexts nested inside a committing
context.
While plperl and pltcl need no changes beyond removing their now-useless
SPI_start_transaction() calls, plpython needs some more work because it
hadn't gotten the memo about catching commit/rollback errors in the
first place. Such an error resulted in longjmp'ing out of the Python
interpreter, which leaks Python stack entries at present and is reported
to crash Python 3.11 altogether. Add the missing logic to catch such
errors and convert them into Python exceptions.
We are probably going to have to back-patch this once Python 3.11 ships,
but it's a sufficiently basic change that I'm a bit nervous about doing
so immediately. Let's let it bake awhile in HEAD first.
Peter Eisentraut and Tom Lane
Discussion: https://postgr.es/m/3375ffd8-d71c-2565-e348-a597d6e739e3@enterprisedb.com
Discussion: https://postgr.es/m/17416-ed8fe5d7213d6c25@postgresql.org
This feature adds row filtering for publication tables. When a publication
is defined or modified, an optional WHERE clause can be specified. Rows
that don't satisfy this WHERE clause will be filtered out. This allows a
set of tables to be partially replicated. The row filter is per table. A
new row filter can be added simply by specifying a WHERE clause after the
table name. The WHERE clause must be enclosed by parentheses.
The row filter WHERE clause for a table added to a publication that
publishes UPDATE and/or DELETE operations must contain only columns that
are covered by REPLICA IDENTITY. The row filter WHERE clause for a table
added to a publication that publishes INSERT can use any column. If the
row filter evaluates to NULL, it is regarded as "false". The WHERE clause
only allows simple expressions that don't have user-defined functions,
user-defined operators, user-defined types, user-defined collations,
non-immutable built-in functions, or references to system columns. These
restrictions could be addressed in the future.
If you choose to do the initial table synchronization, only data that
satisfies the row filters is copied to the subscriber. If the subscription
has several publications in which a table has been published with
different WHERE clauses, rows that satisfy ANY of the expressions will be
copied. If a subscriber is a pre-15 version, the initial table
synchronization won't use row filters even if they are defined in the
publisher.
The row filters are applied before publishing the changes. If the
subscription has several publications in which the same table has been
published with different filters (for the same publish operation), those
expressions get OR'ed together so that rows satisfying any of the
expressions will be replicated.
This means all the other filters become redundant if (a) one of the
publications have no filter at all, (b) one of the publications was
created using FOR ALL TABLES, (c) one of the publications was created
using FOR ALL TABLES IN SCHEMA and the table belongs to that same schema.
If your publication contains a partitioned table, the publication
parameter publish_via_partition_root determines if it uses the partition's
row filter (if the parameter is false, the default) or the root
partitioned table's row filter.
Psql commands \dRp+ and \d <table-name> will display any row filters.
Author: Hou Zhijie, Euler Taveira, Peter Smith, Ajin Cherian
Reviewed-by: Greg Nancarrow, Haiying Tang, Amit Kapila, Tomas Vondra, Dilip Kumar, Vignesh C, Alvaro Herrera, Andres Freund, Wei Wang
Discussion: https://www.postgresql.org/message-id/flat/CAHE3wggb715X%2BmK_DitLXF25B%3DjE6xyNCH4YOwM860JR7HarGQ%40mail.gmail.com
There were a number of places in the code that used bespoke bit-twiddling
expressions to do bitwise rotation. While we've had pg_rotate_right32()
for a while now, we hadn't gotten around to standardizing on that. Do so
now. Since many potential call sites look more natural with the "left"
equivalent, add that function too.
Reviewed by Tom Lane and Yugo Nagata
Discussion:
https://www.postgresql.org/message-id/CAFBsxsH7c1LC0CGZ0ADCBXLHU5-%3DKNXx-r7tHYPAW51b2HK4Qw%40mail.gmail.com
There are two Asserts in nodeMergejoin.c that are reachable if
the input data is not in the expected order. This seems way too
fragile. Alexander Lakhin reported a case where the assertions
could be triggered with misconfigured foreign-table partitions,
and bitter experience with unstable operating system collation
definitions suggests another easy route to hitting them. Neither
Assert is in a place where we can't afford one more test-and-branch,
so replace 'em with plain test-and-elog logic.
Per bug #17395. While the reported symptom is relatively recent,
collation changes could happen anytime, so back-patch to all
supported branches.
Discussion: https://postgr.es/m/17395-8c326292078d1a57@postgresql.org
We assume that direct-modify ForeignScan nodes cannot be re-evaluated
during EvalPlanQual processing, but the rework for inherited
UPDATE/DELETE in commit 86dc90056 changed things, without considering
that, so that such ForeignScan nodes get called as part of the
EvalPlanQual subtree during EvalPlanQual processing in the case of an
inherited UPDATE/DELETE where the inheritance set contains foreign
target relations. To avoid re-evaluating such ForeignScan nodes during
EvalPlanQual processing, commit c3928b467 modified nodeForeignscan.c,
but the assumption made there that ExecForeignScan() should never be
called for such ForeignScan nodes during EvalPlanQual processing turned
out to be wrong in some cases, leading to a segmentation fault or a
"cannot re-evaluate a Foreign Update or Delete during EvalPlanQual"
error.
Fix by modifying nodeForeignscan.c further to avoid re-evaluating such
ForeignScan nodes even in ExecForeignScan()/ExecReScanForeignScan()
during EvalPlanQual processing. Since this makes non-reachable the
test-and-elog added to ForeignNext() by commit c3928b467 that produced
the aforesaid error, convert the test-and-elog to an Assert.
Per bug #17355 from Alexander Lakhin. Back-patch to v14 where both
commits came in.
Patch by me, reviewed and tested by Alexander Lakhin and Amit Langote.
Discussion: https://postgr.es/m/17355-de8e362eb7001a96@postgresql.org
Commit 9dc718bd added a "logically unchanged by UPDATE" hinting
mechanism, which is currently used within nbtree indexes only (see
commit d168b666). This mechanism determined whether or not the incoming
item is a logically unchanged duplicate (a duplicate needed only for
MVCC versioning purposes) once per row updated per non-HOT update. This
approach led to memory leaks which were noticeable with an UPDATE
statement that updated sufficiently many rows, at least on tables that
happen to have an expression index.
On HEAD, fix the issue by adding a cache to the executor's per-index
IndexInfo struct.
Take a different approach on Postgres 14 to avoid an ABI break: simply
pass down the hint to all indexes unconditionally with non-HOT UPDATEs.
This is deemed acceptable because the hint is currently interpreted
within btinsert() as "perform a bottom-up index deletion pass if and
when the only alternative is splitting the leaf page -- prefer to delete
any LP_DEAD-set items first". nbtree must always treat the hint as a
noisy signal about what might work, as a strategy of last resort, with
costs imposed on non-HOT updaters. (The same thing might not be true
within another index AM that applies the hint, which is why the original
behavior is preserved on HEAD.)
Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Klaudie Willis <Klaudie.Willis@protonmail.com>
Diagnosed-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/261065.1639497535@sss.pgh.pa.us
Backpatch: 14-, where the hinting mechanism was added.
Commit 4ace45677 failed to fix the problem fully, because the
same issue of attempting to fetch a non-returnable index column
can occur when rechecking the indexqual after using a lossy index
operator. Moreover, it broke EXPLAIN for such indexquals (which
indicates a gap in our test cases :-().
Revert the code changes of 4ace45677 in favor of adding a new field
to struct IndexOnlyScan, containing a version of the indexqual that
can be executed against the index-returned tuple without using any
non-returnable columns. (The restrictions imposed by check_index_only
guarantee this is possible, although we may have to recompute indexed
expressions.) Support construction of that during setrefs.c
processing by marking IndexOnlyScan.indextlist entries as resjunk
if they can't be returned, rather than removing them entirely.
(We could alternatively require setrefs.c to look up the IndexOptInfo
again, but abusing resjunk this way seems like a reasonably safe way
to avoid needing to do that.)
This solution isn't great from an API-stability standpoint: if there
are any extensions out there that build IndexOnlyScan structs directly,
they'll be broken in the next minor releases. However, only a very
invasive extension would be likely to do such a thing. There's no
change in the Path representation, so typical planner extensions
shouldn't have a problem.
As before, back-patch to all supported branches.
Discussion: https://postgr.es/m/3179992.1641150853@sss.pgh.pa.us
Discussion: https://postgr.es/m/17350-b5bdcf476e5badbb@postgresql.org
The API spec for lookup_rowtype_tupdesc previously said you could use
either ReleaseTupleDesc or DecrTupleDescRefCount. However, the latter
choice means the caller must be certain that the returned tupdesc is
refcounted. I don't recall right now whether that was always true
when this spec was written, but it's certainly not always true since
we introduced shared record typcaches for parallel workers. That means
that callers using DecrTupleDescRefCount are dependent on typcache
behavior details that they probably shouldn't be. Hence, change the API
spec to say that you must call ReleaseTupleDesc, and fix the half-dozen
callers that weren't.
AFAICT this is just future-proofing, there's no live bug here.
So no back-patch.
Per gripe from Chapman Flack.
Discussion: https://postgr.es/m/61B901A4.1050808@anastigmatix.net
Standardize on xoroshiro128** as our basic PRNG algorithm, eliminating
a bunch of platform dependencies as well as fundamentally-obsolete PRNG
code. In addition, this API replacement will ease replacing the
algorithm again in future, should that become necessary.
xoroshiro128** is a few percent slower than the drand48 family,
but it can produce full-width 64-bit random values not only 48-bit,
and it should be much more trustworthy. It's likely to be noticeably
faster than the platform's random(), depending on which platform you
are thinking about; and we can have non-global state vectors easily,
unlike with random(). It is not cryptographically strong, but neither
are the functions it replaces.
Fabien Coelho, reviewed by Dean Rasheed, Aleksander Alekseev, and myself
Discussion: https://postgr.es/m/alpine.DEB.2.22.394.2105241211230.165418@pseudo
It's possible that a subplan below a Memoize node contains a parameter
from above the Memoize node. If this parameter changes then cache entries
may become out-dated due to the new parameter value.
Previously Memoize was mistakenly not aware of this. We fix this here by
flushing the cache whenever a parameter that's not part of the cache
key changes.
Bug: #17213
Reported by: Elvis Pranskevichus
Author: David Rowley
Discussion: https://postgr.es/m/17213-988ed34b225a2862@postgresql.org
Backpatch-through: 14, where Memoize was added
It's possible that a subplan below a Memoize node contains a parameter
from above the Memoize node. If this parameter changes then cache entries
may become out-dated due to the new parameter value.
Previously Memoize was mistakenly not aware of this. We fix this here by
flushing the cache whenever a parameter that's not part of the cache
key changes.
Bug: #17213
Reported by: Elvis Pranskevichus
Author: David Rowley
Discussion: https://postgr.es/m/17213-988ed34b225a2862@postgresql.org
Backpatch-through: 14, where Memoize was added
Memoize would always use the hash equality operator for the cache key
types to determine if the current set of parameters were the same as some
previously cached set. Certain types such as floating points where -0.0
and +0.0 differ in their binary representation but are classed as equal by
the hash equality operator may cause problems as unless the join uses the
same operator it's possible that whichever join operator is being used
would be able to distinguish the two values. In which case we may
accidentally return in the incorrect rows out of the cache.
To fix this here we add a binary mode to Memoize to allow it to the
current set of parameters to previously cached values by comparing
bit-by-bit rather than logically using the hash equality operator. This
binary mode is always used for LATERAL joins and it's used for normal
joins when any of the join operators are not hashable.
Reported-by: Tom Lane
Author: David Rowley
Discussion: https://postgr.es/m/3004308.1632952496@sss.pgh.pa.us
Backpatch-through: 14, where Memoize was added
This undoes a mistake in 1ec7679f1: domainval and domainnull were
meant to live across loop iterations, but they were incorrectly
moved inside the loop. The effect was only to emit useless extra
EEOP_MAKE_READONLY steps, so it's not a big deal; nonetheless,
back-patch to v13 where the mistake was introduced.
Ranier Vilela
Discussion: https://postgr.es/m/CAEudQAqXuhbkaAp-sGH6dR6Nsq7v28_0TPexHOm6FiDYqwQD-w@mail.gmail.com
In the same spirit as 6301c3ada, fix some more places where we were
using list_delete_first() in a loop and thereby risking O(N^2)
behavior. It's not clear that the lists manipulated in these spots
can get long enough to be really problematic ... but it's not clear
that they can't, either, and the fixes are simple enough.
As before, back-patch to v13.
Discussion: https://postgr.es/m/CD2F0E7F-9822-45EC-A411-AE56F14DEA9F@amazon.com
An update such as "UPDATE ... SET fld[n].subfld = whatever"
failed if the array elements were domains rather than plain
composites. That's because isAssignmentIndirectionExpr()
failed to cope with the CoerceToDomain node that would appear
in the expression tree in this case. The result would typically
be a crash, and even if we accidentally didn't crash, we'd not
correctly preserve other fields of the same array element.
Per report from Onder Kalaci. Back-patch to v11 where arrays of
domains came in.
Discussion: https://postgr.es/m/PH0PR21MB132823A46AA36F0685B7A29AD8BD9@PH0PR21MB1328.namprd21.prod.outlook.com
All the tape functions, like LogicalTapeRead and LogicalTapeWrite, now
take a LogicalTape as argument, instead of LogicalTapeSet+tape number.
You can create any number of LogicalTapes in a single LogicalTapeSet, and
you don't need to decide the number upfront, when you create the tape set.
This makes the tape management in hash agg spilling in nodeAgg.c simpler.
Discussion: https://www.postgresql.org/message-id/420a0ec7-602c-d406-1e75-1ef7ddc58d83%40iki.fi
Reviewed-by: Peter Geoghegan, Zhihong Yu, John Naylor
Do not update shm_mq's mq_bytes_written until we have written
an amount of data greater than 1/4th of the ring size, unless
the caller of shm_mq_send(v) requests a flush at the end of
the message. This reduces the number of calls to SetLatch(),
and also the number of CPU cache misses, considerably, and thus
makes shm_mq significantly faster.
Dilip Kumar, reviewed by Zhihong Yu and Tomas Vondra. Some
minor cosmetic changes by me.
Discussion: http://postgr.es/m/CAFiTN-tVXqn_OG7tHNeSkBbN+iiCZTiQ83uakax43y1sQb2OBA@mail.gmail.com
Prior to v14, we insisted that the query in RETURN QUERY be of a type
that returns tuples. (For instance, INSERT RETURNING was allowed,
but not plain INSERT.) That happened indirectly because we opened a
cursor for the query, so spi.c checked SPI_is_cursor_plan(). As a
consequence, the error message wasn't terribly on-point, but at least
it was there.
Commit 2f48ede08 lost this detail. Instead, plain RETURN QUERY
insisted that the query be a SELECT (by checking for SPI_OK_SELECT)
while RETURN QUERY EXECUTE failed to check the query type at all.
Neither of these changes was intended.
The only convenient place to check this in the EXECUTE case is inside
_SPI_execute_plan, because we haven't done parse analysis until then.
So we need to pass down a flag saying whether to enforce that the
query returns tuples. Fortunately, we can squeeze another boolean
into struct SPIExecuteOptions without an ABI break, since there's
padding space there. (It's unlikely that any extensions would
already be using this new struct, but preserving ABI in v14 seems
like a smart idea anyway.)
Within spi.c, it seemed like _SPI_execute_plan's parameter list
was already ridiculously long, and I didn't want to make it longer.
So I thought of passing SPIExecuteOptions down as-is, allowing that
parameter list to become much shorter. This makes the patch a bit
more invasive than it might otherwise be, but it's all internal to
spi.c, so that seems fine.
Per report from Marc Bachmann. Back-patch to v14 where the
faulty code came in.
Discussion: https://postgr.es/m/1F2F75F0-27DF-406F-848D-8B50C7EEF06A@gmail.com
Several mistakes have piled in the code comments over the time,
including incorrect grammar, function names and simple typos. This
commit takes care of a portion of these.
No backpatch is done as this is only cosmetic.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20210924215827.GS831@telsasoft.com
Up to now the size of a query's rangetable has been limited by the
constants INNER_VAR et al, which mustn't be equal to any real
rangetable index. 65000 doubtless seemed like enough for anybody,
and it still is orders of magnitude larger than the number of joins
we can realistically handle. However, we need a rangetable entry
for each child partition that is (or might be) processed by a query.
Queries with a few thousand partitions are getting more realistic,
so that the day when that limit becomes a problem is in sight,
even if it's not here yet. Hence, let's raise the limit.
Rather than just increase the values of INNER_VAR et al, this patch
adopts the approach of making them small negative values, so that
rangetables could theoretically become as long as INT_MAX.
The bulk of the patch is concerned with changing Var.varno and some
related variables from "Index" (unsigned int) to plain "int". This
is basically cosmetic, with little actual effect other than to help
debuggers print their values nicely. As such, I've only bothered
with changing places that could actually see INNER_VAR et al, which
the parser and most of the planner don't. We do have to be careful
in places that are performing less/greater comparisons on varnos,
but there are very few such places, other than the IS_SPECIAL_VARNO
macro itself.
A notable side effect of this patch is that while it used to be
possible to add INNER_VAR et al to a Bitmapset, that will now
draw an error. I don't see any likelihood that it wouldn't be a
bug to include these fake varnos in a bitmapset of real varnos,
so I think this is all to the good.
Although this touches outfuncs/readfuncs, I don't think a catversion
bump is required, since stored rules would never contain Vars
with these fake varnos.
Andrey Lepikhov and Tom Lane, after a suggestion by Peter Eisentraut
Discussion: https://postgr.es/m/43c7f2f5-1e27-27aa-8c65-c91859d15190@postgrespro.ru
The Value node struct is a weird construct. It is its own node type,
but most of the time, it actually has a node type of Integer, Float,
String, or BitString. As a consequence, the struct name and the node
type don't match most of the time, and so it has to be treated
specially a lot. There doesn't seem to be any value in the special
construct. There is very little code that wants to accept all Value
variants but nothing else (and even if it did, this doesn't provide
any convenient way to check it), and most code wants either just one
particular node type (usually String), or it accepts a broader set of
node types besides just Value.
This change removes the Value struct and node type and replaces them
by separate Integer, Float, String, and BitString node types that are
proper node types and structs of their own and behave mostly like
normal node types.
Also, this removes the T_Null node tag, which was previously also a
possible variant of Value but wasn't actually used outside of the
Value contained in A_Const. Replace that by an isnull field in
A_Const.
Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/5ba6bc5b-3f95-04f2-2419-f8ddb4c046fb@enterprisedb.com
All the code paths simplified here were already using a boolean or used
an expression that led to zero or one, making the extra bits
unnecessary.
Author: Justin Pryzby
Reviewed-by: Tom Lane, Michael Paquier, Peter Smith
Discussion: https://postgr.es/m/20210428182936.GE27406@telsasoft.com
Improve two places in plpgsql, and one in spi.c, where an error
message would confusingly tell you that you couldn't use a SELECT
query, when what you had written *was* a SELECT query. The actual
problem is that you can't use SELECT ... INTO in these contexts,
but the messages failed to make that apparent. Special-case
SELECT INTO to make these errors more helpful.
Also, fix the same spots in plpgsql, as well as several messages
in exec_eval_expr(), to not quote the entire complained-of query or
expression in the primary error message. That behavior very easily
led to violating our message style guideline about keeping the primary
error message short and single-line. Also, since the important part
of the message was after the inserted text, it could make the real
problem very hard to see. We can report the query or expression as
the first line of errcontext instead.
Per complaint from Roger Mason. Back-patch to v14, since (a) some
of these messages are new in v14 and (b) v14's translatable strings
are still somewhat in flux. The problem's older than that of
course, but I'm hesitant to change the behavior further back.
Discussion: https://postgr.es/m/1914708.1629474624@sss.pgh.pa.us
The FDW batching code was using the same tuple descriptor both for all
slots (regular and plan slots), but that's incorrect - the subplan may
use a different descriptor. Currently this is benign, because batching
is used only for INSERTs, and in that case the descriptors always match.
But that would change if we allow batching UPDATEs.
Fix by copying the appropriate tuple descriptor. Backpatch to 14, where
the FDW batching was implemented.
Author: Amit Langote
Backpatch-through: 14, where FDW batching was added
Discussion: https://postgr.es/m/CA%2BHiwqEWd5B0-e-RvixGGUrNvGkjH2s4m95%3DJcwUnyV%3Df0rAKQ%40mail.gmail.com
It's not sensible to re-evaluate a direct-modify Foreign Update or Delete
during EvalPlanQual. However, ExecInitForeignScan() can still get called
if a table mixes local and foreign partitions. EvalPlanQualStart() left
the es_result_relations array uninitialized in the child EPQ EState, but
ExecInitForeignScan() still expected to find it. That caused a segfault.
Fix by skipping the es_result_relations lookup during EvalPlanQual
processing. To make things a bit more robust, also skip the
BeginDirectModify calls, and add a runtime check that ExecForeignScan()
is not called on direct-modify foreign scans during EvalPlanQual
processing.
This is new in v14, commit 1375422c78. Before that, EvalPlanQualStart()
copied the whole ResultRelInfo array to the EPQ EState. Backpatch to v14.
Report and diagnosis by Andrey Lepikhov.
Discussion: https://www.postgresql.org/message-id/cb2b808d-cbaa-4772-76ee-c8809bafcf3d%40postgrespro.ru
I failed to account for the possibility that when
ExecAppendAsyncEventWait() notifies multiple async-capable nodes using
postgres_fdw, a preceding node might invoke process_pending_request() to
process a pending asynchronous request made by a succeeding node. In
that case the succeeding node should produce a tuple to return to the
parent Append node from tuples fetched by process_pending_request() when
notified. Repair.
Per buildfarm via Michael Paquier. Back-patch to v14, like the previous
commit.
Thanks to Tom Lane for testing.
Discussion: https://postgr.es/m/YQP0UPT8KmPiHTMs%40paquier.xyz
A pending asynchronous request is handled by process_pending_request(),
which previously not only processed an in-progress remote query but
performed ExecForeignScan() to produce a tuple to return to the local
server asynchronously from the result of the remote query. But that led
to a server crash when executing a query or led to an "InstrStartNode
called twice in a row" or "InstrEndLoop called on running node" failure
when doing EXPLAIN ANALYZE of it, in cases where the plan tree for it
contained multiple async-capable nodes accessing the same
initplan/subplan that contained multiple async-capable nodes scanning
the same foreign tables as for the parent async-capable nodes, as
reported by Andrey Lepikhov. The reason is that the second step in
process_pending_request() invoked when executing the initplan/subplan
for one of the parent async-capable nodes caused recursive execution of
the initplan/subplan for another of the parent async-capable nodes.
To fix, split process_pending_request() into the two steps and postpone
the second step until ForeignAsyncConfigureWait() is called for each of
the pending asynchronous requests. Also, in ExecAppendAsyncEventWait()
we assumed that FDWs would register at least one wait event in a
WaitEventSet created there when they were called from
ForeignAsyncConfigureWait() in that function, but allow FDWs to register
zero wait events in the WaitEventSet; modify ExecAppendAsyncEventWait()
to just return in that case.
Oversight in commit 27e1f1456. Back-patch to v14 where that commit went
in.
Andrey Lepikhov and Etsuro Fujita
Discussion: https://postgr.es/m/fe5eaa19-1704-e4a4-76ee-3b9d37ade399@postgrespro.ru
The point of introducing the hash_mem_multiplier GUC was to let users
reproduce the old behavior of hash aggregation, i.e. that it could use
more than work_mem at need. However, the implementation failed to get
the job done on Win64, where work_mem is clamped to 2GB to protect
various places that calculate memory sizes using "long int". As
written, the same clamp was applied to hash_mem. This resulted in
severe performance regressions for queries requiring a bit more than
2GB for hash aggregation, as they now spill to disk and there's no
way to stop that.
Getting rid of the work_mem restriction seems like a good idea, but
it's a big job and could not conceivably be back-patched. However,
there's only a fairly small number of places that are concerned with
the hash_mem value, and it turns out to be possible to remove the
restriction there without too much code churn or any ABI breaks.
So, let's do that for now to fix the regression, and leave the
larger task for another day.
This patch does introduce a bit more infrastructure that should help
with the larger task, namely pg_bitutils.h support for working with
size_t values.
Per gripe from Laurent Hasson. Back-patch to v13 where the
behavior change came in.
Discussion: https://postgr.es/m/997817.1627074924@sss.pgh.pa.us
Discussion: https://postgr.es/m/MN2PR15MB25601E80A9B6D1BA6F592B1985E39@MN2PR15MB2560.namprd15.prod.outlook.com
Datum sorts can be significantly faster than tuple sorts, especially when
the data type being sorted is a pass-by-value type. Something in the
region of 50-70% performance improvements appear to be possible.
Just in case there's any confusion; the Datum sort is only used when the
targetlist of the Sort node contains a single column, not when there's a
single column in the sort key and multiple items in the target list.
Author: Ronan Dunklau
Reviewed-by: James Coleman, David Rowley, Ranier Vilela, Hou Zhijie
Tested-by: John Naylor
Discussion: https://postgr.es/m/3177670.itZtoPt7T5@aivenronan
Follow-up to 2ed532ee8c, a few error
messages in the logical replication area currently only deal with
tables, but if we're anticipating more relkinds such as sequences
being handled, then these messages also fall into the category
affected by the previous patch, so adjust them too.
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/c9ba5c6a-4bd5-e12c-1b3c-edbcaedbf392@enterprisedb.com
"Result Cache" was never a great name for this node, but nobody managed
to come up with another name that anyone liked enough. That was until
David Johnston mentioned "Node Memoization", which Tom Lane revised to
just "Memoize". People seem to like "Memoize", so let's do the rename.
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/20210708165145.GG1176@momjian.us
Backpatch-through: 14, where Result Cache was introduced
Similar to 50e17ad28, which allowed hash tables to be used for IN clauses
with a set of constants, here we add the same feature for NOT IN clauses.
NOT IN evaluates the same as: WHERE a <> v1 AND a <> v2 AND a <> v3.
Obviously, if we're using a hash table we must be exactly equivalent to
that and return the same result taking into account that either side of
the condition could contain a NULL. This requires a little bit of
special handling to make work with the hash table version.
When processing NOT IN, the ScalarArrayOpExpr's operator will be the <>
operator. To be able to build and lookup a hash table we must use the
<>'s negator operator. The planner checks if that exists and is hashable
and sets the relevant fields in ScalarArrayOpExpr to instruct the executor
to use hashing.
Author: David Rowley, James Coleman
Reviewed-by: James Coleman, Zhihong Yu
Discussion: https://postgr.es/m/CAApHDvoF1mum_FRk6D621edcB6KSHBi2+GAgWmioj5AhOu2vwQ@mail.gmail.com
Previously, all CustomScan providers had to support projections,
but there may be cases where this is inconvenient. Add a flag
bit to say if it's supported.
Important item for the release notes: this is non-backwards-compatible
since the default is now to assume that CustomScan providers can't
project, instead of assuming that they can. It's fail-soft, but could
result in visible performance penalties due to adding unnecessary
Result nodes.
Sven Klemm, reviewed by Aleksander Alekseev; some cosmetic fiddling
by me.
Discussion: https://postgr.es/m/CAMCrgp1kyakOz6c8aKhNDJXjhQ1dEjEnp+6KNT3KxPrjNtsrDg@mail.gmail.com
Here we alter the code that calls build_pertrans_for_aggref() so that the
function no longer needs to special-case whether it's dealing with an
aggtransfn or an aggcombinefn. This allows us to reuse the
build_aggregate_transfn_expr() function and just get rid of the
build_aggregate_combinefn_expr() completely.
All of the special case code that was in build_pertrans_for_aggref() has
been moved up to the calling functions.
This saves about a dozen lines of code in nodeAgg.c and a few dozen more
in parse_agg.c
Also, rename a few variables in nodeAgg.c to try to make it more clear
that we're working with either a aggtransfn or an aggcombinefn. Some of
the old names would have you believe that we were always working with an
aggtransfn.
Discussion: https://postgr.es/m/CAApHDvptMQ9FmF0D67zC_w88yVnoNVR2+kkOQGUrCmdxWxLULQ@mail.gmail.com
In the "simple Query" code path, it's fine for parse analysis or
execution of a utility statement to scribble on the statement's node
tree, since that'll just be thrown away afterwards. However it's
not fine if the node tree is in the plan cache, as then it'd be
corrupted for subsequent executions. Up to now we've dealt with
that by having individual utility-statement functions apply
copyObject() if they were going to modify the tree. But that's
prone to errors of omission. Bug #17053 from Charles Samborski
shows that CREATE/ALTER DOMAIN didn't get this memo, and can
crash if executed repeatedly from plan cache.
In the back branches, we'll just apply a narrow band-aid for that,
but in HEAD it seems prudent to have a more principled fix that
will close off the possibility of other similar bugs in future.
Hence, let's hoist the responsibility for doing copyObject up into
ProcessUtility from its children, thus ensuring that it happens for
all utility statement types.
Also, modify ProcessUtility's API so that its callers can tell it
whether a copy step is necessary. It turns out that in all cases,
the immediate caller knows whether the node tree is transient, so
this doesn't involve a huge amount of code thrashing. In this way,
while we lose a little bit in the execute-from-cache code path due
to sometimes copying node trees that wouldn't be mutated anyway,
we gain something in the simple-Query code path by not copying
throwaway node trees. Statements that are complex enough to be
expensive to copy are almost certainly ones that would have to be
copied anyway, so the loss in the cache code path shouldn't be much.
(Note that this whole problem applies only to utility statements.
Optimizable statements don't have the issue because we long ago made
the executor treat Plan trees as read-only. Perhaps someday we will
make utility statement execution act likewise, but I'm not holding
my breath.)
Discussion: https://postgr.es/m/931771.1623893989@sss.pgh.pa.us
Discussion: https://postgr.es/m/17053-3ca3f501bbc212b4@postgresql.org
Commit b676ac443b optimized handling of tuple slots with bulk inserts
into foreign tables, so that the slots are initialized only once and
reused for all batches. The data was however copied into the slots only
after the initialization, inserting duplicate values when the slot gets
reused. Fixed by moving the ExecCopySlot outside the init branch.
The existing postgres_fdw tests failed to catch this due to inserting
data into foreign tables without unique indexes, and then checking only
the number of inserted rows. This adds a new test with both a unique
index and a check of inserted values.
Reported-by: Alexander Pyhalov
Discussion: https://postgr.es/m/7a8cf8d56b3d18e5c0bccd6cd42d04ac%40postgrespro.ru
Commit b663a41363 introduced bulk inserts for FDW, but the handling of
tuple slots turned out to be problematic for two reasons. Firstly, the
slots were re-created for each individual batch. Secondly, all slots
referenced the same tuple descriptor - with reasonably small batches
this is not an issue, but with large batches this triggers O(N^2)
behavior in the resource owner code.
These two issues work against each other - to reduce the number of times
a slot has to be created/dropped, larger batches are needed. However,
the larger the batch, the more expensive the resource owner gets. For
practical batch sizes (100 - 1000) this would not be a big problem, as
the benefits (latency savings) greatly exceed the resource owner costs.
But for extremely large batches it might be much worse, possibly even
losing with non-batching mode.
Fixed by initializing tuple slots only once (and reusing them across
batches) and by using a new tuple descriptor copy for each slot.
Discussion: https://postgr.es/m/ebbbcc7d-4286-8c28-0272-61b4753af761%40enterprisedb.com
We've accumulated quite a mix of instances of "an SQL" and "a SQL" in the
documents. It would be good to be a bit more consistent with these.
The most recent version of the SQL standard I looked at seems to prefer
"an SQL". That seems like a good lead to follow, so here we change all
instances of "a SQL" to become "an SQL". Most instances correctly use
"an SQL" already, so it also makes sense to use the dominant variation in
order to minimise churn.
Additionally, there were some other abbreviations that needed to be
adjusted. FSM, SSPI, SRF and a few others. Also fix some pronounceable,
abbreviations to use "a" instead of "an". For example, "a SASL" instead
of "an SASL".
Here I've only adjusted the documents and error messages. Many others
still exist in source code comments. Translator hint comments seem to be
the biggest culprit. It currently does not seem worth the churn to change
these.
Discussion: https://postgr.es/m/CAApHDvpML27UqFXnrYO1MJddsKVMQoiZisPvsAGhKE_tsKXquw%40mail.gmail.com
Commit 2453ea142 redefined pg_proc.proargtypes to include the types of
OUT parameters, for procedures only. While that had some advantages
for implementing the SQL-spec behavior of DROP PROCEDURE, it was pretty
disastrous from a number of other perspectives. Notably, since the
primary key of pg_proc is name + proargtypes, this made it possible to
have multiple procedures with identical names + input arguments and
differing output argument types. That would make it impossible to call
any one of the procedures by writing just NULL (or "?", or any other
data-type-free notation) for the output argument(s). The change also
seems likely to cause grave confusion for client applications that
examine pg_proc and expect the traditional definition of proargtypes.
Hence, revert the definition of proargtypes to what it was, and
undo a number of complications that had been added to support that.
To support the SQL-spec behavior of DROP PROCEDURE, when there are
no argmode markers in the command's parameter list, we perform the
lookup both ways (that is, matching against both proargtypes and
proallargtypes), succeeding if we get just one unique match.
In principle this could result in ambiguous-function failures
that would not happen when using only one of the two rules.
However, overloading of procedure names is thought to be a pretty
rare usage, so this shouldn't cause many problems in practice.
Postgres-specific code such as pg_dump can defend against any
possibility of such failures by being careful to specify argmodes
for all procedure arguments.
This also fixes a few other bugs in the area of CALL statements
with named parameters, and improves the documentation a little.
catversion bump forced because the representation of procedures
with OUT arguments changes.
Discussion: https://postgr.es/m/3742981.1621533210@sss.pgh.pa.us
Previously, we left the EPQ sub-executor alone until ExecEndLockRows.
This caused any buffer pins or other resources that it might hold to
remain held until ExecutorEnd, which in some code paths means that
they are held till the Portal is closed. That can cause user-visible
problems, such as blocking VACUUM; and it's unlike the behavior of
ordinary table-scanning nodes, which will have released all buffer
pins by the time they return an EOF indication.
We can make LockRows work more like other plan nodes by calling
EvalPlanQualEnd just before returning NULL. We still need to call it
in ExecEndLockRows in case the node was not run to completion, but in
the normal case the second call does nothing and costs little.
Per report from Yura Sokolov. In principle this is a longstanding
bug, but in view of the lack of other complaints and the low severity
of the consequences, I chose not to back-patch.
Discussion: https://postgr.es/m/4aa370cb91ecf2f9885d98b80ad1109c@postgrespro.ru
In cases where run-time pruning isn't required, the synchronous and
asynchronous subplans for an async-aware Append node determined using
classify_matching_subplans() should be re-used when rescanning the node,
but the previous code re-determined them using that function repeatedly
each time when rescanning the node, leading to incorrect results in a
normal build and an Assert failure in an Assert-enabled build as that
function doesn't assume that it's called repeatedly in such cases. Fix
the code as mentioned above.
My oversight in commit 27e1f1456.
While at it, initialize async-related pointers/variables to NULL/zero
explicitly in ExecInitAppend() and ExecReScanAppend(), just to be sure.
(The variables would have been set to zero before we get to the latter
function, but let's do so.)
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/CAPmGK16Q4B2_KY%2BJH7rb7wQbw54AUprp7TMekGTd2T1B62yysQ%40mail.gmail.com
When the planner considered using a Result Cache node to cache results
from the inner side of a Nested Loop Join, it failed to consider that the
inner path's parameterization may not be the entire join condition. If
the join was marked as inner_unique then we may accidentally put the cache
in singlerow mode. This meant that entries would be marked as complete
after caching the first row. That was wrong as if only part of the join
condition was parameterized then the uniqueness of the unique join was not
guaranteed at the Result Cache's level. The uniqueness is only guaranteed
after Nested Loop applies the join filter. If subsequent rows were found,
this would lead to:
ERROR: cache entry already complete
This could have been fixed by only putting the cache in singlerow mode if
the entire join condition was parameterized. However, Nested Loop will
only read its inner side so far as the first matching row when the join is
unique, so that might mean we never get an opportunity to mark cache
entries as complete. Since non-complete cache entries are useless for
subsequent lookups, we just don't bother considering a Result Cache path
in this case.
In passing, remove the XXX comment that claimed the above ERROR might be
better suited to be an Assert. After there being an actual case which
triggered it, it seems better to keep it an ERROR.
Reported-by: David Christensen
Discussion: https://postgr.es/m/CAOxo6X+dy-V58iEPFgst8ahPKEU+38NZzUuc+a7wDBZd4TrHMQ@mail.gmail.com
We consider this supported (though I've got my doubts that it's a
good idea, because tableoid is not immutable). However, several
code paths failed to fill the field in soon enough, causing such
a GENERATED expression to see zero or the wrong value. This
occurred when ALTER TABLE adds a new GENERATED column to a table
with existing rows, and during regular INSERT or UPDATE on a
foreign table with GENERATED columns.
Noted during investigation of a report from Vitaly Ustinov.
Back-patch to v12 where GENERATED came in.
Discussion: https://postgr.es/m/CAM_DEiWR2DPT6U4xb-Ehigozzd3n3G37ZB1+867zbsEVtYoJww@mail.gmail.com
COMMIT/ROLLBACK necessarily destroys all snapshots within the session.
The original implementation of intra-procedure transactions just
cavalierly did that, ignoring the fact that this left us executing in
a rather different environment than normal. In particular, it turns
out that handling of toasted datums depends rather critically on there
being an outer ActiveSnapshot: otherwise, when SPI or the core
executor pop whatever snapshot they used and return, it's unsafe to
dereference any toasted datums that may appear in the query result.
It's possible to demonstrate "no known snapshots" and "missing chunk
number N for toast value" errors as a result of this oversight.
Historically this outer snapshot has been held by the Portal code,
and that seems like a good plan to preserve. So add infrastructure
to pquery.c to allow re-establishing the Portal-owned snapshot if it's
not there anymore, and add enough bookkeeping support that we can tell
whether it is or not.
We can't, however, just re-establish the Portal snapshot as part of
COMMIT/ROLLBACK. As in normal transaction start, acquiring the first
snapshot should wait until after SET and LOCK commands. Hence, teach
spi.c about doing this at the right time. (Note that this patch
doesn't fix the problem for any PLs that try to run intra-procedure
transactions without using SPI to execute SQL commands.)
This makes SPI's no_snapshots parameter rather a misnomer, so in HEAD,
rename that to allow_nonatomic.
replication/logical/worker.c also needs some fixes, because it wasn't
careful to hold a snapshot open around AFTER trigger execution.
That code doesn't use a Portal, which I suspect someday we're gonna
have to fix. But for now, just rearrange the order of operations.
This includes back-patching the recent addition of finish_estate()
to centralize the cleanup logic there.
This also back-patches commit 2ecfeda3e into v13, to improve the
test coverage for worker.c (it was that test that exposed that
worker.c's snapshot management is wrong).
Per bug #15990 from Andreas Wicht. Back-patch to v11 where
intra-procedure COMMIT was added.
Discussion: https://postgr.es/m/15990-eee2ac466b11293d@postgresql.org
This seems to be leftover from ea15e1867 and from when we used to evaluate
SRFs at each node.
Since there is an unconditional "return" at the end of the loop body, only
1 loop is ever possible, so we can just change this into an if condition.
There is no actual bug being fixed here so no back-patch. It seems fine to
just fix this anomaly in master only.
Author: Greg Nancarrow
Discussion: https://postgr.es/m/CAJcOf-d7T1q0az-D8evWXnsuBZjigT04WkV5hCAOEJQZRWy28w@mail.gmail.com
Also "make reformat-dat-files".
The only change worthy of note is that pgindent messed up the formatting
of launcher.c's struct LogicalRepWorkerId, which led me to notice that
that struct wasn't used at all anymore, so I just took it out.
EXPLAIN ANALYZE for an async-capable ForeignScan node associated with
postgres_fdw is done just by using instrumentation for ExecProcNode()
called from the node's callbacks, causing the following problems:
1) If the remote table to scan is empty, the node is incorrectly
considered as "never executed" by the command even if the node is
executed, as ExecProcNode() isn't called from the node's callbacks at
all in that case.
2) The command fails to collect timings for things other than
ExecProcNode() done in the node, such as creating a cursor for the
node's remote query.
To fix these problems, add instrumentation for async-capable nodes, and
modify postgres_fdw accordingly.
My oversight in commit 27e1f1456.
While at it, update a comment for the AsyncRequest struct in execnodes.h
and the documentation for the ForeignAsyncRequest API in fdwhandler.sgml
to match the code in ExecAsyncAppendResponse() in nodeAppend.c, and fix
typos in comments in nodeAppend.c.
Per report from Andrey Lepikhov, though I didn't use his patch.
Reviewed-by: Andrey Lepikhov
Discussion: https://postgr.es/m/2eb662bb-105d-fc20-7412-2f027cc3ca72%40postgrespro.ru
It's unusual to have any resjunk columns in an ON CONFLICT ... UPDATE
list, but it can happen when MULTIEXPR_SUBLINK SubPlans are present.
If it happens, the ON CONFLICT UPDATE code path would end up storing
tuples that include the values of the extra resjunk columns. That's
fairly harmless in the short run, but if new columns are added to
the table then the values would become accessible, possibly leading
to malfunctions if they don't match the datatypes of the new columns.
This had escaped notice through a confluence of missing sanity checks,
including
* There's no cross-check that a tuple presented to heap_insert or
heap_update matches the table rowtype. While it's difficult to
check that fully at reasonable cost, we can easily add assertions
that there aren't too many columns.
* The output-column-assignment cases in execExprInterp.c lacked
any sanity checks on the output column numbers, which seems like
an oversight considering there are plenty of assertion checks on
input column numbers. Add assertions there too.
* We failed to apply nodeModifyTable's ExecCheckPlanOutput() to
the ON CONFLICT UPDATE tlist. That wouldn't have caught this
specific error, since that function is chartered to ignore resjunk
columns; but it sure seems like a bad omission now that we've seen
this bug.
In HEAD, the right way to fix this is to make the processing of
ON CONFLICT UPDATE tlists work the same as regular UPDATE tlists
now do, that is don't add "SET x = x" entries, and use
ExecBuildUpdateProjection to evaluate the tlist and combine it with
old values of the not-set columns. This adds a little complication
to ExecBuildUpdateProjection, but allows removal of a comparable
amount of now-dead code from the planner.
In the back branches, the most expedient solution seems to be to
(a) use an output slot for the ON CONFLICT UPDATE projection that
actually matches the target table, and then (b) invent a variant of
ExecBuildProjectionInfo that can be told to not store values resulting
from resjunk columns, so it doesn't try to store into nonexistent
columns of the output slot. (We can't simply ignore the resjunk columns
altogether; they have to be evaluated for MULTIEXPR_SUBLINK to work.)
This works back to v10. In 9.6, projections work much differently and
we can't cheaply give them such an option. The 9.6 version of this
patch works by inserting a JunkFilter when it's necessary to get rid
of resjunk columns.
In addition, v11 and up have the reverse problem when trying to
perform ON CONFLICT UPDATE on a partitioned table. Through a
further oversight, adjust_partition_tlist() discarded resjunk columns
when re-ordering the ON CONFLICT UPDATE tlist to match a partition.
This accidentally prevented the storing-bogus-tuples problem, but
at the cost that MULTIEXPR_SUBLINK cases didn't work, typically
crashing if more than one row has to be updated. Fix by preserving
resjunk columns in that routine. (I failed to resist the temptation
to add more assertions there too, and to do some minor code
beautification.)
Per report from Andres Freund. Back-patch to all supported branches.
Security: CVE-2021-32028
While we were (mostly) careful about ensuring that the dimensions of
arrays aren't large enough to cause integer overflow, the lower bound
values were generally not checked. This allows situations where
lower_bound + dimension overflows an integer. It seems that that's
harmless so far as array reading is concerned, except that array
elements with subscripts notionally exceeding INT_MAX are inaccessible.
However, it confuses various array-assignment logic, resulting in a
potential for memory stomps.
Fix by adding checks that array lower bounds aren't large enough to
cause lower_bound + dimension to overflow. (Note: this results in
disallowing cases where the last subscript position would be exactly
INT_MAX. In principle we could probably allow that, but there's a lot
of code that computes lower_bound + dimension and would need adjustment.
It seems doubtful that it's worth the trouble/risk to allow it.)
Somewhat independently of that, array_set_element() was careless
about possible overflow when checking the subscript of a fixed-length
array, creating a different route to memory stomps. Fix that too.
Security: CVE-2021-32027
In 9eacee2e6, I included some code to verify the cache's memory tracking
is correct by counting up the number of entries and the memory they use
each time we evict something from the cache. Those values are then
compared to the expected values using Assert. The problem is that this
requires looping over the entire cache hash table each time we evict an
entry from the cache. That can be pretty expensive, as noted by Pavel
Stehule.
Here we move this memory accounting checking code so that we only verify
it on cassert builds once when shutting down the Result Cache node.
Aside from the performance increase, this has two distinct advantages:
1) We do the memory checks at the last possible moment before destroying
the cache. This means we'll now catch accounting problems that might
sneak in after a cache eviction.
2) We now do the memory Assert checks when there were no cache evictions.
This increases the coverage.
One small disadvantage is that we'll now miss any memory tracking issues
that somehow managed to resolve themselves by the end of execution.
However, it seems to me that such a memory tracking problem would be quite
unlikely, and likely somewhat less harmful if one were to exist.
In passing, adjust the loop over the hash table to use the standard
simplehash.h method of iteration.
Reported-by: Pavel Stehule
Discussion: https://postgr.es/m/CAFj8pRAzgoSkdEiqrKbT=7yG9FA5fjUAP3jmJywuDqYq6Ki5ug@mail.gmail.com
This is cleanup for commit 27e1f1456:
* ExecAppendAsyncEventWait(), which was modified a bit further by commit
a8af856d3, duplicated the same nevents calculation. Simplify the code
a little bit to avoid the duplication. Update comments there.
* Add an assertion to ExecAppendAsyncRequest().
* Update a comment about merging the async_capable options from input
relations in merge_fdw_options(), per complaint from Kyotaro Horiguchi.
* Add a comment for fetch_more_data_begin().
Author: Etsuro Fujita
Discussion: https://postgr.es/m/CAPmGK1637W30Wx3MnrReewhafn6F_0J76mrJGoFXFnpPq4QfvA%40mail.gmail.com
Adopt a more consistent policy about what slot-type-specific
getsysattr functions should do when system attributes are not
available. To wit, they should all throw the same user-oriented
error, rather than variously crashing or emitting developer-oriented
messages.
This closes a identifiable problem in commits a71cfc56b and
3fb93103a (in v13 and v12), so back-patch into those branches,
along with a test case to try to ensure we don't break it again.
It is not known that any of the former crash cases are reachable
in HEAD, but this seems like a good safety improvement in any case.
Discussion: https://postgr.es/m/141051591267657@mail.yandex.ru
