A previous commit replaced all the calls to this function with
durable_rename() as of dac1ff3, making it used nowhere in the tree.
Using it in extension code is also risky based on the issues described
in this previous commit, so let's remove it. This makes possible the
removal of HAVE_WORKING_LINK.
Author: Nathan Bossart
Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13
Use it for RelationSyncEntry->streamed_txns, which is currently using an
integer list.
The API support is not complete, not because it is hard to write but
because it's unclear that it's worth the code space, there being so
little use of XID lists.
Discussion: https://postgr.es/m/202205130830.g5ntonhztspb@alvherre.pgsql
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
pg_attribute_nonnull(...) can be used to generate compiler warnings
when a function is called with the specified arguments set to NULL, as
per an idea from Andres Freund. An empty argument list indicates that
no pointer arguments can be NULL. pg_attribute_nonnull() only works for
compilers that support the nonnull function attribute. If nonnull is
not supported, pg_attribute_nonnull() has no effect.
As a beginning, this commit uses it for the DefineCustomXXXVariable()
functions to generate warnings when the "name" and "value" arguments are
set to NULL. This will likely be expanded to other places in the
future, where it makes sense.
Author: Nathan Bossart
Reviewed by: Michael Paquier, Tom Lane
Discussion: https://postgr.es/m/20220525061739.ur7x535vtzyzkmqo@alap3.anarazel.de
There were many calls to construct_array() and deconstruct_array() for
built-in types, for example, when dealing with system catalog columns.
These all hardcoded the type attributes necessary to pass to these
functions.
To simplify this a bit, add construct_array_builtin(),
deconstruct_array_builtin() as wrappers that centralize this hardcoded
knowledge. This simplifies many call sites and reduces the amount of
hardcoded stuff that is spread around.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/2914356f-9e5f-8c59-2995-5997fc48bcba%40enterprisedb.com
TransactionIdIsInProgress had a fast path to return 'false' if the
single-item CLOG cache said that the transaction was known to be
committed. However, that was wrong, because a transaction is first
marked as committed in the CLOG but doesn't become visible to others
until it has removed its XID from the proc array. That could lead to an
error:
ERROR: t_xmin is uncommitted in tuple to be updated
or for an UPDATE to go ahead without blocking, before the previous
UPDATE on the same row was made visible.
The window is usually very short, but synchronous replication makes it
much wider, because the wait for synchronous replica happens in that
window.
Another thing that makes it hard to hit is that it's hard to get such
a commit-in-progress transaction into the single item CLOG cache.
Normally, if you call TransactionIdIsInProgress on such a transaction,
it determines that the XID is in progress without checking the CLOG
and without populating the cache. One way to prime the cache is to
explicitly call pg_xact_status() on the XID. Another way is to use a
lot of subtransactions, so that the subxid cache in the proc array is
overflown, making TransactionIdIsInProgress rely on pg_subtrans and
CLOG checks.
This has been broken ever since it was introduced in 2008, but the race
condition is very hard to hit, especially without synchronous
replication. There were a couple of reports of the error starting from
summer 2021, but no one was able to find the root cause then.
TransactionIdIsKnownCompleted() is now unused. In 'master', remove it,
but I left it in place in backbranches in case it's used by extensions.
Also change pg_xact_status() to check TransactionIdIsInProgress().
Previously, it only checked the CLOG, and returned "committed" before
the transaction was actually made visible to other queries. Note that
this also means that you cannot use pg_xact_status() to reproduce the
bug anymore, even if the code wasn't fixed.
Report and analysis by Konstantin Knizhnik. Patch by Simon Riggs, with
the pg_xact_status() change added by me.
Author: Simon Riggs
Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/flat/4da7913d-398c-e2ad-d777-f752cf7f0bbb%40garret.ru
Previously, we encoded both NULL and the first byte at the base address
as 0. That confusion led to the assertion in commit e07d4ddc, which
failed when min_dynamic_shared_memory was used. Give them distinct
encodings, by switching to 1-based offsets for non-NULL pointers. Also
improve macro hygiene in passing (missing/misplaced parentheses), and
remove open-coded access to the raw offset value from freepage.c/h.
Although e07d4ddc was back-patched to 10, the only code that actually
makes use of relptr at the base address arrived in 84b1c63a, so no need
to back-patch further than 14 for now.
Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/20220519193839.GT19626%40telsasoft.com
This reverts commits 5753d4ee32 and fe60b67250 that modified HOT to
ignore BRIN indexes. The commit message for 5753d4ee32 claims that:
When determining whether an index update may be skipped by using
HOT, we can ignore attributes indexed only by BRIN indexes. There
are no index pointers to individual tuples in BRIN, and the page
range summary will be updated anyway as it relies on visibility
info.
This is partially incorrect - it's true BRIN indexes don't point to
individual tuples, so HOT chains are not an issue, but the visibitlity
info is not sufficient to keep the index up to date. This can easily
result in corrupted indexes, as demonstrated in the hackers thread.
This does not mean relaxing the HOT restrictions for BRIN is a lost
cause, but it needs to handle the two aspects (allowing HOT chains and
updating the page range summaries) as separate. But that requires a
major changes, and it's too late for that in the current dev cycle.
Reported-by: Tomas Vondra
Discussion: https://postgr.es/m/05ebcb44-f383-86e3-4f31-0a97a55634cf@enterprisedb.com
We were not updating the partition map cache in the subscriber even when
the corresponding remote rel is changed. Due to this data was getting
incorrectly replicated for partition tables after the publisher has
changed the table schema.
Fix it by resetting the required entries in the partition map cache after
receiving a new relation mapping from the publisher.
Reported-by: Shi Yu
Author: Shi Yu, Hou Zhijie
Reviewed-by: Amit Langote, Amit Kapila
Backpatch-through: 13, where it was introduced
Discussion: https://postgr.es/m/OSZPR01MB6310F46CD425A967E4AEF736FDA49@OSZPR01MB6310.jpnprd01.prod.outlook.com
The original advice for hard-wired SetConfigOption calls was to use
PGC_S_OVERRIDE, particularly for PGC_INTERNAL GUCs. However,
that's really overkill for PGC_INTERNAL GUCs, since there is no
possibility that we need to override a user-provided setting.
Instead use PGC_S_DYNAMIC_DEFAULT in most places, so that the
value will appear with source = 'default' in pg_settings and thereby
not be shown by psql's new \dconfig command. The one exception is
that when changing in_hot_standby in a hot-standby session, we still
use PGC_S_OVERRIDE, because people felt that seeing that in \dconfig
would be a good thing.
Similarly use PGC_S_DYNAMIC_DEFAULT for the auto-tune value of
wal_buffers (if possible, that is if wal_buffers wasn't explicitly
set to -1), and for the typical 2MB value of max_stack_depth.
In combination these changes remove four not-very-interesting
entries from the typical output of \dconfig, all of which people
fingered as "why is that showing up?" in the discussion thread.
Discussion: https://postgr.es/m/3118455.1649267333@sss.pgh.pa.us
With the old logic, when the reciever had not yet attached, we would
never call shm_mq_inc_bytes_written(), even if force_flush = true
was specified. That could result in a situation where data that the
sender believes it has sent is never received.
Along the way, remove a useless function prototype for a nonexistent
function from shm_mq.h.
Commit 46846433a0 introduced these
problems.
Pavan Deolasee, with a few changes by me.
Discussion: https://postgr.es/m/CABOikdPkwtLLCTnzzmpSMXo3QZa2yXq0J7Q61ssdLFAJYrOVvQ@mail.gmail.com
Commit 1a36bc9db (SQL/JSON query functions) introduced STRING as a
type_func_name_keyword, thereby breaking applications that use
"string" as a table name, column name, function parameter name, etc.
That seems like a pretty bad thing, not least because the SQL spec
says that STRING is an unreserved keyword.
This is easy enough to fix so far as the core grammar is concerned.
However, doing so causes some ECPG test cases to fail, specifically
those that use "string" as a typedef name. It turns out this is
because portions of the ECPG grammar allow type_func_name_keywords
but not unreserved_keywords as typedef names. That's pretty horrid,
and it's mildly astonishing that we've not heard complaints about it
before. We can fix two of those uses trivially, but the ones in the
var_type production are less easy. As a stopgap, hard-code STRING as
an allowed alternative in var_type.
Per report from Alastair McKinley.
Discussion: https://postgr.es/m/3661437.1653855582@sss.pgh.pa.us
Several places in the planner tried to clamp a double value to fit
in a "long" by doing
(long) Min(x, (double) LONG_MAX);
This is subtly incorrect, because it casts LONG_MAX to double and
potentially back again. If long is 64 bits then the double value
is inexact, and the platform might round it up to LONG_MAX+1
resulting in an overflow and an undesirably negative output.
While it's not hard to rewrite the expression into a safe form,
let's put it into a common function to reduce the risk of someone
doing it wrong in future.
In principle this is a bug fix, but since the problem could only
manifest with group count estimates exceeding 2^63, it seems unlikely
that anyone has actually hit this or will do so anytime soon. We're
fixing it mainly to satisfy fuzzer-type tools. That being the case,
a HEAD-only fix seems sufficient.
Andrey Lepikhov
Discussion: https://postgr.es/m/ebbc2efb-7ef9-bf2f-1ada-d6ec48f70e58@postgrespro.ru
This is a slight, convenient semantics change from what commit
0f0cfb4940 ("Fix parallel operations that prevent oldest xmin from
advancing") introduced that lets us simplify the coding in the one place
where it is used.
Backpatch to 13. This is related to commit 6fea65508a ("Tighten
ComputeXidHorizons' handling of walsenders") rewriting the code site
where this is used, which has not yet been backpatched, but it may well
be in the future.
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/202204191637.eldwa2exvguw@alvherre.pgsql
Commit 923def9a53 and 52e4f0cd47 allowed to specify column lists and row
filters for publication tables. This commit extends the
pg_publication_tables view and pg_get_publication_tables function to
display that information.
This information will be useful to users and we also need this for the
later commit that prohibits combining multiple publications with different
column lists for the same table.
Author: Hou Zhijie
Reviewed By: Amit Kapila, Alvaro Herrera, Shi Yu, Takamichi Osumi
Discussion: https://postgr.es/m/202204251548.mudq7jbqnh7r@alvherre.pgsql
I started out with the intention to rename value_type to item_type to
avoid a collision with a typedef name that appears on some platforms.
Along the way, I noticed that the adjacent field "format" was not being
correctly handled by the backend/nodes/ infrastructure functions:
copyfuncs.c erroneously treated it as a scalar, while equalfuncs,
outfuncs, and readfuncs omitted handling it at all. This looks like
it might be cosmetic at the moment because the field is always NULL
after parse analysis; but that's likely a bug in itself, and the code's
certainly not very future-proof. Let's fix it while we can still do so
without forcing an initdb on beta testers.
Further study found a few other inconsistencies in the backend/nodes/
infrastructure for the recently-added JSON node types, so fix those too.
catversion bumped because of potential change in stored rules.
Discussion: https://postgr.es/m/526703.1652385613@sss.pgh.pa.us
Currently, preloaded libraries are expected to request additional
shared memory and LWLocks in _PG_init(). However, it is not unusal
for such requests to depend on MaxBackends, which won't be
initialized at that time. Such requests could also depend on GUCs
that other modules might change. This introduces a new hook where
modules can safely use MaxBackends and GUCs to request additional
shared memory and LWLocks.
Furthermore, this change restricts requests for shared memory and
LWLocks to this hook. Previously, libraries could make requests
until the size of the main shared memory segment was calculated.
Unlike before, we no longer silently ignore requests received at
invalid times. Instead, we FATAL if someone tries to request
additional shared memory or LWLocks outside of the hook.
Nathan Bossart and Julien Rouhaud
Discussion: https://postgr.es/m/20220412210112.GA2065815%40nathanxps13
Discussion: https://postgr.es/m/Yn2jE/lmDhKtkUdr@paquier.xyz
Run renumber_oids.pl to move high-numbered OIDs down, as per pre-beta
tasks specified by RELEASE_CHANGES. For reference, the command was
./renumber_oids.pl --first-mapped-oid 8000 --target-oid 6205
Three variables in pqsignal.h (UnBlockSig, BlockSig and StartupBlockSig)
were not marked with PGDLLIMPORT, as they are declared in a way that
prevents mark_pgdllimport.pl to detect them. These variables are
redefined in a style more consistent with the other headers, allowing
the script to find and mark them.
PGDLLIMPORT was missing for __pg_log_level in logging.h, so add it
back. The marking got accidentally removed in 9a374b77, just after its
addition in 8ec5694.
While on it, add a comment in mark_pgdllimport.pl explaining what are
the arguments needed by the script (aka a list of header paths).
Reported-by: Andres Freund
Discussion: https://postgr.es/m/20220506234924.6mxxotl3xl63db3l@alap3.anarazel.de
The code for unloading a library has been commented-out for over 12
years, ever since commit 602a9ef5a7, and we're
no closer to supporting it now than we were back then.
Nathan Bossart, reviewed by Michael Paquier and by me.
Discussion: http://postgr.es/m/Ynsc9bRL1caUSBSE@paquier.xyz
The problem is that we don't send keep-alive messages for a long time
while processing large transactions during logical replication where we
don't send any data of such transactions. This can happen when the table
modified in the transaction is not published or because all the changes
got filtered. We do try to send the keep_alive if necessary at the end of
the transaction (via WalSndWriteData()) but by that time the
subscriber-side can timeout and exit.
To fix this we try to send the keepalive message if required after
processing certain threshold of changes.
Reported-by: Fabrice Chapuis
Author: Wang wei and Amit Kapila
Reviewed By: Masahiko Sawada, Euler Taveira, Hou Zhijie, Hayato Kuroda
Backpatch-through: 10
Discussion: https://postgr.es/m/CAA5-nLARN7-3SLU_QUxfy510pmrYK6JJb=bk3hcgemAM_pAv+w@mail.gmail.com
697492434 added 3 new quicksort specialization functions for common
datatypes.
That commit was not very consistent in how it would determine if we're
compiling for 32-bit or 64-bit machines. It would sometimes use
USE_FLOAT8_BYVAL and at other times check if SIZEOF_DATUM == 8. This
could cause theoretical problems due to the way USE_FLOAT8_BYVAL is now
defined based on SIZEOF_VOID_P >= 8. If pointers for some reason were
ever larger than 8-bytes then we'd end up doing 32-bit comparisons
mistakenly. Let's just always check SIZEOF_DATUM >= 8.
It also seems that ssup_datum_signed_cmp is just never used on 32-bit
builds, so let's just ifdef that out to make sure we never accidentally
use that comparison function on such machines. This also allows us to
ifdef out 1 of the 3 new specialization quicksort functions in 32-bit
builds which seems to shrink down the binary by over 4KB on my machine.
In passing, also add the missing DatumGetInt32() / DatumGetInt64() macros
in the comparison functions.
Discussion: https://postgr.es/m/CAApHDvqcQExRhtRa9hJrJB_5egs3SUfOcutP3m+3HO8A+fZTPA@mail.gmail.com
Reviewed-by: John Naylor
Commits 4eb21763 and b74e94dc introduced a way to force every backend to
close all relation files, to fix an ancient Windows-only bug.
This commit extends that behavior to all operating systems and adds
a couple of extra barrier points, to fix a totally different class of
bug: the reuse of relfilenodes in scenarios that have no other kind of
cache invalidation to prevent file descriptor mix-ups.
In all releases, data corruption could occur when you moved a database
to another tablespace and then back again. Despite that, no back-patch
for now as the infrastructure required is too new and invasive. In
master only, since commit aa010514, it could also happen when using
CREATE DATABASE with a user-supplied OID or via pg_upgrade.
Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/20220209220004.kb3dgtn2x2k2gtdm%40alap3.anarazel.de
With sufficiently bad luck, it was possible for IssuePendingWritebacks()
to reopen a file after we'd processed PROCSIGNAL_BARRIER_SMGRRELEASE and
before the file was unlinked by some other backend. That left a small
hole in commit 4eb21763's plan to fix all spurious errors from DROP
TABLESPACE and similar on Windows.
Fix by closing md.c's segments, instead of just closing fd.c's
descriptors, and then teaching smgrwriteback() not to open files that
aren't already open.
Reported-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/20220209220004.kb3dgtn2x2k2gtdm%40alap3.anarazel.de
The test for lz4.h used AC_CHECK_HEADERS, but nothing was using the
resulting symbol HAVE_LZ4_H. Change this to use AC_CHECK_HEADER
instead. This was probably an oversight, seeing that the nearby
similar tests do this correctly.
Instability in the test for pg_walinspect revealed that
pg_get_wal_records_info_till_end_of_wal(x) would try to decode all the
records with a start LSN earlier than the flush LSN, even though that
might include a partial record at the end of the range. In that case,
read_local_xlog_page_no_wait() would return NULL when it tried to read
past the flush LSN, which would be interpreted as an error by the
caller. That caused a test failure only on a BF animal that had been
restarted recently, but could be expected to happen in the wild quite
easily depending on the alignment of various parameters.
Fix by using private data in read_local_xlog_page_no_wait() to signal
end-of-wal to the caller, so that it can be properly distinguished
from a real error.
Discussion: https://postgr.es/m/Ymd/e5eeZMNAkrXo%40paquier.xyz
Discussion: https://postgr.es/m/111657.1650910309@sss.pgh.pa.us
Authors: Thomas Munro, Bharath Rupireddy.
This reverts commits 2c902bb and ccfbd92. Per buildfarm members
kestrel, rorqual and calliphoridae, the assertions checking that a TLI
history file should not exist when created by a WAL receiver have been
failing, and switching to durable_rename() over durable_rename_excl()
would cause the newest TLI history file to overwrite the existing one.
We need to think harder about such cases, so revert the new logic for
now.
Note that all the failures have been reported in the test
025_stuck_on_old_timeline.
Discussion: https://postgr.es/m/511362.1651116498@sss.pgh.pa.us
ccfbd92 has replaced all existing in-core callers of this function in
favor of durable_rename(). durable_rename_excl() is by nature unsafe on
crashes happening at the wrong time, so just remove it.
Author: Nathan Bossart
Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13
inline_cte() expected to find exactly as many references to the
target CTE as its cterefcount indicates. While that should be
accurate for the tree as emitted by the parser, there are some
optimizations that occur upstream of here that could falsify it,
notably removal of unused subquery output expressions.
Trying to make the accounting 100% accurate seems expensive and
doomed to future breakage. It's not really worth it, because
all this code is protecting is downstream assumptions that every
referenced CTE has a plan. Let's convert those assertions to
regular test-and-elog just in case there's some actual problem,
and then drop the failing assertion.
Per report from Tomas Vondra (thanks also to Richard Guo for
analysis). Back-patch to v12 where the faulty code came in.
Discussion: https://postgr.es/m/29196a1e-ed47-c7ca-9be2-b1c636816183@enterprisedb.com
Commit aa0105141 assigned fixed OIDs to template0 and postgres
in a very ad-hoc way. Notably, instead of teaching Catalog.pm
about these OIDs, the unused_oids script was just hacked to
not show them as unused. That's problematic since, for example,
duplicate_oids wouldn't report any future conflict. Hence,
invent a macro DECLARE_OID_DEFINING_MACRO() that can be used to
define an OID that is known to Catalog.pm and will participate
in duplicate-detection as well as renumbering by renumber_oids.pl.
(We don't anticipate renumbering these particular OIDs, but we
might as well build out all the Catalog.pm infrastructure while
we're here.)
Another issue is that aa0105141 neglected to touch IsPinnedObject,
with the result that it now claimed template0 and postgres are
pinned. The right thing to do there seems to be to teach it that
no database is pinned, since in fact DROP DATABASE doesn't check
for pinned-ness (and at least for these cases, that is an
intentional choice). It's not clear whether this wrong answer
had any visible effect, but perhaps it could have resulted in
erroneous management of dependency entries.
In passing, rename the TemplateDbOid macro to Template1DbOid
to reduce confusion (likely we should have done that way back
when we invented template0, but we didn't), and rename the
OID macros for template0 and postgres to have a similar style.
There are no changes to postgres.bki here, so no need for a
catversion bump.
Discussion: https://postgr.es/m/2935358.1650479692@sss.pgh.pa.us
This is needed so that renumber_oids.pl can handle renumbering
shared catalog declarations, which need to provide C macros for
the OIDs of the shared toast table and index. The previous
method of writing a C macro separately was error-prone anyway.
Also teach renumber_oids.pl about DECLARE_UNIQUE_INDEX_PKEY,
as we missed doing when inventing that macro.
There are no changes to postgres.bki here, so no need for a
catversion bump.
Discussion: https://postgr.es/m/2995325.1650487527@sss.pgh.pa.us
psql, pg_dump, and pg_amcheck share code to process object name
patterns like 'foo*.bar*' to match all tables with names starting in
'bar' that are in schemas starting with 'foo'. Before v14, any number
of extra name parts were silently ignored, so a command line '\d
foo.bar.baz.bletch.quux' was interpreted as '\d bletch.quux'. In v14,
as a result of commit 2c8726c4b0, we
instead treated this as a request for table quux in a schema named
'foo.bar.baz.bletch'. That caused problems for people like Justin
Pryzby who were accustomed to copying strings of the form
db.schema.table from messages generated by PostgreSQL itself and using
them as arguments to \d.
Accordingly, revise things so that if an object name pattern contains
more parts than we're expecting, we throw an error, unless there's
exactly one extra part and it matches the current database name.
That way, thisdb.myschema.mytable is accepted as meaning just
myschema.mytable, but otherdb.myschema.mytable is an error, and so
is some.random.garbage.myschema.mytable.
Mark Dilger, per report from Justin Pryzby and discussion among
various people.
Discussion: https://www.postgresql.org/message-id/20211013165426.GD27491%40telsasoft.com
ComputeXidHorizons (nee GetOldestXmin) thought that it could identify
walsenders by checking for proc->databaseId == 0. Perhaps that was
safe when the code was written, but it's been wrong at least since
autovacuum was invented. Background processes that aren't connected
to any particular database, such as the autovacuum launcher and
logical replication launcher, look like that too.
This imprecision is harmful because when such a process advertises an
xmin, the result is to hold back dead-tuple cleanup in all databases,
though it'd be sufficient to hold it back in shared catalogs (which
are the only relations such a process can access). Aside from being
generally inefficient, this has recently been seen to cause regression
test failures in the buildfarm, as a consequence of the logical
replication launcher's startup transaction preventing VACUUM from
marking pages of a user table as all-visible.
We only want that global hold-back effect for the case where a
walsender is advertising a hot standby feedback xmin. Therefore,
invent a new PGPROC flag that says that a process' xmin should be
considered globally, and check that instead of using the incorrect
databaseId == 0 test. Currently only a walsender sets that flag,
and only if it is not connected to any particular database. (This is
for bug-compatibility with the undocumented behavior of the existing
code, namely that feedback sent by a client who has connected to a
particular database would not be applied globally. I'm not sure this
is a great definition; however, such a client is capable of issuing
plain SQL commands, and I don't think we want xmins advertised for
such commands to be applied globally. Perhaps this could do with
refinement later.)
While at it, I rewrote the comment in ComputeXidHorizons, and
re-ordered the commented-upon if-tests, to make them match up
for intelligibility's sake.
This is arguably a back-patchable bug fix, but given the lack of
complaints I think it prudent to let it age awhile in HEAD first.
Discussion: https://postgr.es/m/1346227.1649887693@sss.pgh.pa.us
Only 1 of 3 of these changes appear to be handled by pgindent. That change
is new to v15. The remaining two appear to be left alone by pgindent. The
exact reason for that is not 100% clear to me. It seems related to the
fact that it's a line that contains *only* a single line comment and no
actual code. It does not seem worth investigating this in too much
detail. In any case, these do not conform to our usual practices, so fix
them.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20220411020336.GB26620@telsasoft.com
heap_fetch() used to have a "keep_buf" parameter that told it to return
ownership of the buffer pin to the caller after finding that the
requested tuple TID exists but is invisible to the specified snapshot.
This was thoughtlessly removed in commit 5db6df0c0, which broke
heapam_tuple_lock() (formerly EvalPlanQualFetch) because that function
needs to do more accesses to the tuple even if it's invisible. The net
effect is that we would continue to touch the page for a microsecond or
two after releasing pin on the buffer. Usually no harm would result;
but if a different session decided to defragment the page concurrently,
we could see garbage data and mistakenly conclude that there's no newer
tuple version to chain up to. (It's hard to say whether this has
happened in the field. The bug was actually found thanks to a later
change that allowed valgrind to detect accesses to non-pinned buffers.)
The most reasonable way to fix this is to reintroduce keep_buf,
although I made it behave slightly differently: buffer ownership
is passed back only if there is a valid tuple at the requested TID.
In HEAD, we can just add the parameter back to heap_fetch().
To avoid an API break in the back branches, introduce an additional
function heap_fetch_extended() in those branches.
In HEAD there is an additional, less obvious API change: tuple->t_data
will be set to NULL in all cases where buffer ownership is not returned,
in particular when the tuple exists but fails the time qual (and
!keep_buf). This is to defend against any other callers attempting to
access non-pinned buffers. We concluded that making that change in back
branches would be more likely to introduce problems than cure any.
In passing, remove a comment about heap_fetch that was obsoleted by
9a8ee1dc6.
Per bug #17462 from Daniil Anisimov. Back-patch to v12 where the bug
was introduced.
Discussion: https://postgr.es/m/17462-9c98a0f00df9bd36@postgresql.org
The last usage of this argument in this routine can be tracked down to
7e2f9062, aka 11 years ago. Getting rid of this argument can also be an
advantage for extensions calling check_index_is_clusterable(), as it
removes any need to worry about the meaning of what a recheck would be
at this level.
Author: Justin Pryzby
Discussion: https://postgr.es/m/20220411140609.GF26620@telsasoft.com
This reverts commits 0147fc7, 4567596, aa64f23, and 5ecd018.
There is no longer agreement that introducing this function
was the right way to address the problem. The consensus now
seems to favor trying to make a correct value for MaxBackends
available to mdules executing their _PG_init() functions.
Nathan Bossart
Discussion: http://postgr.es/m/20220323045229.i23skfscdbvrsuxa@jrouhaud
