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help / color / mirror / Atom feedFrom: Samba Siva Reddy Chinta <sambasivareddy.ch@zohomail.in>
To: pgsql-hackers <pgsql-hackers@lists.postgresql.org>
Subject: [PATCH] Add hook for plugins to acquire sample rows during ANALYZE
Date: Fri, 26 Jun 2026 07:16:54 +0530
Message-ID: <19f019bc9d0.45f9a6aa271083.5147864197130401189@zohomail.in> (raw)
Hi all,
Attached is a patch that adds a hook, AcquireSampleRowsFunc_hook, allowing extensions to override the row sampling function used during ANALYZE for regular heap relations.
Motivation
Extensions that implement horizontal scaling of tables currently have no clean way to participate in ANALYZE's row sampling. The default acquire_sample_rows() only knows how to sample the local heap, so a distributed-table extension wanting accurate statistics has to either:
maintain its own separate stats-collection machinery outside of ANALYZE entirely, or
duplicate/reimplement parts of analyze.c's sampling logic to pull rows from remote nodes.
This hook lets such an extension plug into the existing ANALYZE code path and supply its own row acquisition function, without having to reinvent stats collection or duplicate logic that already exists in core.
What the patch does
Adds AcquireSampleRowsFunc_hook (typed identically to AcquireSampleRowsFunc) in vacuum.h.
In analyze.c, both analyze_rel() and acquire_inherited_sample_rows() check the hook and use it in place of acquire_sample_rows() when set.
Adds doc text in xfunc.sgml describing the hook's contract (fill rows[] up to targrows, set *totalrows).
Adds a regression test confirming ANALYZE still completes normally with the hook unset (the hook itself needs a C extension to exercise meaningfully, so this just guards against regressions in the unset case).
​Regards,
Samba Siva Reddy
http://sambasivareddy.in
Attachments:
[application/octet-stream] v1-acquire-sample-rows-hook.patch (7.2K, ../19f019bc9d0.45f9a6aa271083.5147864197130401189@zohomail.in/3-v1-acquire-sample-rows-hook.patch)
download | inline diff:
From 1c2009a823e1922e3a1a2b280626abbe11a86696 Mon Sep 17 00:00:00 2001
From: Samba Siva <sambasivareddy.ch@zohomail.in>
Date: Fri, 29 May 2026 18:05:45 +0530
Subject: [PATCH] Add hook for plugins to acquire sample rows during ANALYZE
- Introduced AcquireSampleRowsFunc_hook for extensions to override row sampling.
- Updated analyze.c to utilize the hook if registered.
- Added tests to ensure ANALYZE completes without errors with the new hook.
---
doc/src/sgml/xfunc.sgml | 10 ++++++++++
src/backend/commands/analyze.c | 24 ++++++++++++++++++++----
src/include/commands/vacuum.h | 11 +++++++++++
src/test/regress/expected/analyze.out | 20 ++++++++++++++++++++
src/test/regress/parallel_schedule | 1 +
src/test/regress/sql/analyze.sql | 24 ++++++++++++++++++++++++
6 files changed, 86 insertions(+), 4 deletions(-)
create mode 100644 src/test/regress/expected/analyze.out
create mode 100644 src/test/regress/sql/analyze.sql
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 1eb5abffd8..f1ef025ae2 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -4203,4 +4203,14 @@ supportfn(internal) returns internal
To create such conditions, the support function must implement
the <literal>SupportRequestIndexCondition</literal> request type.
</para>
+
+ <para>
+ The hook variable <varname>AcquireSampleRowsFunc_hook</varname> allows extensions
+ to override the row sampling function during <command>ANALYZE</command> for regular
+ heap relations. This is useful for extensions/systems which implement distributed
+ databases and want to sample rows from remote nodes instead of the local heap.
+ The hook function fills the provided <literal>rows[]</literal> buffer with at most
+ <literal>targrows</literal> heap tuples and sets <literal>*totalrows</literal> to the
+ estimated total live row count of the relation.
+ </para>
</sect1>
diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 4fffb76e55..3560acdff1 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -74,6 +74,8 @@ int default_statistics_target = 100;
static MemoryContext anl_context = NULL;
static BufferAccessStrategy vac_strategy;
+/* Hook for plugins to acquire sample rows for ANALYZE */
+AcquireSampleRowsFunc_hook_type AcquireSampleRowsFunc_hook = NULL;
static void do_analyze_rel(Relation onerel,
VacuumParams *params, List *va_cols,
@@ -188,8 +190,15 @@ analyze_rel(Oid relid, RangeVar *relation,
if (onerel->rd_rel->relkind == RELKIND_RELATION ||
onerel->rd_rel->relkind == RELKIND_MATVIEW)
{
- /* Regular table, so we'll use the regular row acquisition function */
- acquirefunc = acquire_sample_rows;
+ /*
+ * Regular table, so we'll use the regular row acquisition function.
+ * If a plugin has registered a hook to acquire sample rows, use it;
+ * otherwise use the default function.
+ */
+ if (AcquireSampleRowsFunc_hook)
+ acquirefunc = AcquireSampleRowsFunc_hook;
+ else
+ acquirefunc = acquire_sample_rows;
/* Also get regular table's size */
relpages = RelationGetNumberOfBlocks(onerel);
}
@@ -1467,8 +1476,15 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
if (childrel->rd_rel->relkind == RELKIND_RELATION ||
childrel->rd_rel->relkind == RELKIND_MATVIEW)
{
- /* Regular table, so use the regular row acquisition function */
- acquirefunc = acquire_sample_rows;
+ /*
+ * Regular table, so use the regular row acquisition function.
+ * If a plugin has registered a hook to acquire sample rows, use it;
+ * otherwise use the default function.
+ */
+ if (AcquireSampleRowsFunc_hook)
+ acquirefunc = AcquireSampleRowsFunc_hook;
+ else
+ acquirefunc = acquire_sample_rows;
relpages = RelationGetNumberOfBlocks(childrel);
}
else if (childrel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index bc37a80dc7..146f936861 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -21,6 +21,7 @@
#include "catalog/pg_class.h"
#include "catalog/pg_statistic.h"
#include "catalog/pg_type.h"
+#include "foreign/fdwapi.h"
#include "parser/parse_node.h"
#include "storage/buf.h"
#include "storage/lock.h"
@@ -113,6 +114,9 @@ typedef void (*AnalyzeAttrComputeStatsFunc) (VacAttrStatsP stats,
int samplerows,
double totalrows);
+/* Hook type for plugins to acquire sample rows for ANALYZE */
+typedef AcquireSampleRowsFunc AcquireSampleRowsFunc_hook_type;
+
typedef struct VacAttrStats
{
/*
@@ -334,6 +338,13 @@ extern PGDLLIMPORT int vacuum_cost_limit;
extern PGDLLIMPORT int64 parallel_vacuum_worker_delay_ns;
+/*
+ * Hook for plugins to override row sampling during ANALYZE.
+ * Also applies to child relations of partitioned/inherited tables.
+ * See acquire_sample_rows() in src/backend/commands/analyze.c.
+ */
+extern PGDLLIMPORT AcquireSampleRowsFunc_hook_type AcquireSampleRowsFunc_hook;
+
/* in commands/vacuum.c */
extern void ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel);
extern void vacuum(List *relations, VacuumParams *params,
diff --git a/src/test/regress/expected/analyze.out b/src/test/regress/expected/analyze.out
new file mode 100644
index 0000000000..5bb6bbc45b
--- /dev/null
+++ b/src/test/regress/expected/analyze.out
@@ -0,0 +1,20 @@
+-- Test AcquireSampleRowsFunc_hook
+-- Usually this would be tested via a C extension.
+-- Here we just confirm this does not break the existing ANALYZE code
+-- by verifying that ANALYZE completes without error.
+CREATE TABLE employees (
+ id SERIAL PRIMARY KEY,
+ name TEXT,
+ department TEXT,
+ salary NUMERIC
+);
+INSERT INTO employees
+ SELECT
+ i,
+ 'Employee ' || i,
+ 'Department ' || (i % 5),
+ (i % 100) * 1000 + 50000
+ FROM generate_series(1, 1000) i;
+-- Should complete without error
+ANALYZE employees;
+DROP TABLE employees;
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index e1e0c54019..71978ef858 100644
--- a/src/test/regress/parallel_schedule
+++ b/src/test/regress/parallel_schedule
@@ -94,6 +94,7 @@ test: vacuum_parallel
# Run this alone, because concurrent DROP TABLE would make non-superuser
# "ANALYZE;" fail with "relation with OID $n does not exist".
test: maintain_every
+test: analyze
# no relation related tests can be put in this group
test: publication subscription
diff --git a/src/test/regress/sql/analyze.sql b/src/test/regress/sql/analyze.sql
new file mode 100644
index 0000000000..e0bc84e9f9
--- /dev/null
+++ b/src/test/regress/sql/analyze.sql
@@ -0,0 +1,24 @@
+-- Test AcquireSampleRowsFunc_hook
+-- Usually this would be tested via a C extension.
+-- Here we just confirm this does not break the existing ANALYZE code
+-- by verifying that ANALYZE completes without error.
+
+CREATE TABLE employees (
+ id SERIAL PRIMARY KEY,
+ name TEXT,
+ department TEXT,
+ salary NUMERIC
+);
+
+INSERT INTO employees
+ SELECT
+ i,
+ 'Employee ' || i,
+ 'Department ' || (i % 5),
+ (i % 100) * 1000 + 50000
+ FROM generate_series(1, 1000) i;
+
+-- Should complete without error
+ANALYZE employees;
+
+DROP TABLE employees;
--
2.50.1 (Apple Git-155)
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Subject: Re: [PATCH] Add hook for plugins to acquire sample rows during ANALYZE
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