Previously, it would not have worked for a caller to pass a slab
context, since it would have been used for other things which likely
had incompatible size. In an attempt to be helpful and avoid possible
space wastage due to aset's power-of-two rounding, RT_CREATE would
create an additional slab context if the value type was fixed-length
and larger than pointer size. The problem was, we have since added
the bump context type, and the generation context was a possibility as
well, so silently overriding the caller's choice may actually be worse.
Commit e8a6f1f908 arranged so that the caller-provided context is
used only for leaves, so it's safe for the caller to use slab here
if they wish. As demonstration, use slab in one of the radix tree
regression tests.
Reviewed by Masahiko Sawada
Discussion: https://postgr.es/m/CANWCAZZDCo4k5oURg_pPxM6+WZ1oiG=sqgjmQiELuyP0Vtrwig@mail.gmail.com
Previously, this was notionally used only for the entry point of the
tree and as a convenient parent for other contexts.
For shared memory, the creator previously allocated the entry point
in this context, but attaching backends didn't have access to that,
so they just used the caller's context. For the sake of consistency,
allocate every instance of an entry point in the caller's context.
For local memory, allocate the control object in the caller's context
as well. This commit also makes the "leaf context" the notional parent
of the child contexts used for nodes, so it's a bit of a misnomer,
but a future commit will make the node contexts independent rather
than children, so leave it this way for now to avoid code churn.
The memory context parameter for RT_CREATE is now unused in the case
of shared memory, so remove it and adjust callers to match.
In passing, remove unused "context" member from struct TidStore,
which seems to have been an oversight.
Reviewed by Masahiko Sawada
Discussion: https://postgr.es/m/CANWCAZZDCo4k5oURg_pPxM6+WZ1oiG=sqgjmQiELuyP0Vtrwig@mail.gmail.com
Typically only one iterator is present at any time, so it's overkill
to devote an entire context for this. Get rid of it and use the
caller's context.
This is tidy-up work, so no backpatch in this form. However, a
hypothetical extension to v17 that tried to start iteration from
an attaching backend would result in a crash, so that'll be fixed
separately in a way that doesn't change behavior in core.
Patch by me, reported and reviewed by Masahiko Sawada
Discussion: https://postgr.es/m/CAD21AoBB2U47V=F+wQRB1bERov_of5=BOZGaybjaV8FLQyqG3Q@mail.gmail.com
When #include'ing radixtree.h with RT_SHMEM, it could happen to raise
compiler errors due to missing some declarations of types and
functions.
This commit also removes the inclusion of postgres.h since it's
against our usual convention.
Backpatch to v17, where radixtree.h was introduced.
Reviewed-by: Heikki Linnakangas, Álvaro Herrera
Discussion: https://postgr.es/m/CAD21AoCU9YH%2Bb9Rr8YRw7UjmB%3D1zh8GKQkWNiuN9mVhMvkyrRg%40mail.gmail.com
Backpatch-through: 17
RT_NODE_16_SEARCH_EQ() performs comparisions using vector registers
on x64-64 and aarch64. We apply a mask to the resulting bitfield
to eliminate irrelevant bits that may be set. This ensures correct
behavior, but Valgrind complains of the partially-uninitialised
values. So far the warnings have only occurred on aarch64, which
explains why this hasn't been seen earlier.
To fix this warning, initialize the whole fixed-sized part of the nodes
upon allocation, rather than just do the minimum initialization to
function correctly. The initialization for node48 is a bit different
in that the 256-byte slot index array must be populated with "invalid
index" rather than zero. Experimentation has shown that compilers
tend to emit code that uselessly memsets that array twice. To avoid
pessimizing this path, swap the order of the slot_idxs[] and isset[]
arrays so we can initialize with two non-overlapping memset calls.
Reported by Tomas Vondra
Analysis and patch by Tom Lane, reviewed by Masahiko Sawada. I
investigated the behavior of memset calls to overlapping regions,
leading to the above tweaks to node48 as discussed in the thread.
Discussion: https://postgr.es/m/120c63ad-3d12-415f-a7bf-3da451c31bf6%40enterprisedb.com
- Bring memory context names in line with other naming
- Fix typos, reported off-list by Alexander Lakhin
- Remove copy-paste errors from comments
- Remove duplicate #undef
Also, fix a memory leak when updating from non-embeddable to
embeddable. Both were unreachable without adding C code.
Reported-by: Noah Misch
Author: Noah Misch
Reviewed-by: Masahiko Sawada, John Naylor
Discussion: https://postgr.es/m/20240424210319.4c.nmisch%40google.com
This fixes various typos, duplicated words, and tiny bits of whitespace
mainly in code comments but also in docs.
Author: Daniel Gustafsson <daniel@yesql.se>
Author: Heikki Linnakangas <hlinnaka@iki.fi>
Author: Alexander Lakhin <exclusion@gmail.com>
Author: David Rowley <dgrowleyml@gmail.com>
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/3F577953-A29E-4722-98AD-2DA9EFF2CBB8@yesql.se
Previously, the decision to store values in leaves or within the child
pointer was made at compile time, with variable length values using
leaves by necessity. This commit allows introspecting the length of
variable length values at runtime for that decision. This requires
the ability to tell whether the last-level child pointer is actually
a value, so we use a pointer tag in the lowest level bit.
Use this in TID store. This entails adding a byte to the header to
reserve space for the tag. Commit f35bd9bf3 stores up to three offsets
within the header with no bitmap, and now the header can be embedded
as above. This reduces worst-case memory usage when TIDs are sparse.
Reviewed (in an earlier version) by Masahiko Sawada
Discussion: https://postgr.es/m/CANWCAZYw+_KAaUNruhJfE=h6WgtBKeDG32St8vBJBEY82bGVRQ@mail.gmail.com
Discussion: https://postgr.es/m/CAD21AoBci3Hujzijubomo1tdwH3XtQ9F89cTNQ4bsQijOmqnEw@mail.gmail.com
Coverity complained about the integer handling issue; if we start with
an arbitrary non-negative shift value, the loop may decrement it down
to something less than zero before exiting. This commit adds an
assertion to make sure the 'shift' is always 0 after the loop, and
uses 0 as the shift to get the key chunk in the following operation.
Introduced by ee1b30f12.
Reported-by: Tom Lane as per coverity
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/2089517.1711299216%40sss.pgh.pa.us
This implements a radix tree data structure based on the design in
"The Adaptive Radix Tree: ARTful Indexing for Main-Memory Databases"
by Viktor Leis, Alfons Kemper, and ThomasNeumann, 2013. The main
technique that makes it adaptive is using several different node types,
each with a different capacity of elements, and a different algorithm
for accessing them. The nodes start small and grow/shrink as needed.
The main advantage over hash tables is efficient sorted iteration and
better memory locality when successive keys are lexicographically
close together. The implementation currently assumes 64-bit integer
keys, and traversing the tree is in general slower than a linear
probing hash table, so this is not a general-purpose associative array.
The paper describes two other techniques not implemented here,
namely "path compression" and "lazy expansion". These can further
reduce memory usage and speed up traversal, but the former would add
significant complexity and the latter requires storing the full key
with the value. We do trivially compress the path when leading bytes
of the key are zeros, however.
For value storage, we use "combined pointer/value slots", as
recommended in the paper. Values of size equal or smaller than the the
platform's pointer type are stored in the array of child pointers in
the last level node, while larger values are each stored in a separate
allocation. This is for now fixed at compile time, but it would be
fairly trivial to allow determining at runtime how variable-length
values are stored.
One innovation in our implementation compared to the ART paper is
decoupling the notion of node "size class" from "kind". The size
classes within a given node kind have the same underlying type, but
a variable capacity for children, so we can introduce additional node
sizes with little additional code.
To enable different use cases to specialize for different value types
and for shared/local memory, we use macro-templatized code generation
in the same manner as simplehash.h and sort_template.h.
Future commits will use this infrastructure for storing TIDs.
Patch by Masahiko Sawada and John Naylor, but a substantial amount of
credit is due to Andres Freund, whose proof-of-concept was a valuable
source of coding idioms and awareness of performance pitfalls, and
who reviewed earlier versions.
Discussion: https://postgr.es/m/CAD21AoAfOZvmfR0j8VmZorZjL7RhTiQdVttNuC4W-Shdc2a-AA%40mail.gmail.com
