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pg_dump: Simplify query for retrieving attribute statistics.

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This query fetches information from pg_stats, which did not return
table OIDs until recent commit 3b88e50d6c.  Because of this, we had
to cart around arrays of schema and table names, and we needed an
extra filter clause to hopefully convince the planner to use the
correct index.  With the introduction of pg_stats.tableid, we can
instead just use an array of OIDs, and we no longer need the extra
filter clause hack.

Author: Corey Huinker <corey.huinker@gmail.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CADkLM%3DcoCVy92QkVUUTLdo5eO2bMDtwMrzRn_8miAhX%2BuPaqXg%40mail.gmail.com
This commit is contained in:
Nathan Bossart 2026-03-17 11:32:40 -05:00
parent 2eb6cd327c
commit 4b5ba0c4ca
2 changed files with 54 additions and 12 deletions
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65
src/bin/pg_dump/pg_dump.c
View file

@ -7227,6 +7227,7 @@ getRelationStatistics(Archive *fout, DumpableObject *rel, int32 relpages,
dobj->components |= DUMP_COMPONENT_STATISTICS;
dobj->name = pg_strdup(rel->name);
dobj->namespace = rel->namespace;
info->relid = rel->catId.oid;
info->relpages = relpages;
info->reltuples = pstrdup(reltuples);
info->relallvisible = relallvisible;
@ -11122,6 +11123,7 @@ static PGresult *
fetchAttributeStats(Archive *fout)
{
ArchiveHandle *AH = (ArchiveHandle *) fout;
PQExpBuffer relids = createPQExpBuffer();
PQExpBuffer nspnames = createPQExpBuffer();
PQExpBuffer relnames = createPQExpBuffer();
int count = 0;
@ -11157,6 +11159,7 @@ fetchAttributeStats(Archive *fout)
restarted = true;
}
appendPQExpBufferChar(relids, '{');
appendPQExpBufferChar(nspnames, '{');
appendPQExpBufferChar(relnames, '{');
@ -11168,15 +11171,28 @@ fetchAttributeStats(Archive *fout)
*/
for (; te != AH->toc && count < max_rels; te = te->next)
{
if ((te->reqs & REQ_STATS) != 0 &&
strcmp(te->desc, "STATISTICS DATA") == 0)
if ((te->reqs & REQ_STATS) == 0 ||
strcmp(te->desc, "STATISTICS DATA") != 0)
continue;
if (fout->remoteVersion >= 190000)
{
RelStatsInfo *rsinfo = (RelStatsInfo *) te->defnDumperArg;
char relid[32];
sprintf(relid, "%u", rsinfo->relid);
appendPGArray(relids, relid);
}
else
{
appendPGArray(nspnames, te->namespace);
appendPGArray(relnames, te->tag);
count++;
}
count++;
}
appendPQExpBufferChar(relids, '}');
appendPQExpBufferChar(nspnames, '}');
appendPQExpBufferChar(relnames, '}');
@ -11186,14 +11202,25 @@ fetchAttributeStats(Archive *fout)
PQExpBuffer query = createPQExpBuffer();
appendPQExpBufferStr(query, "EXECUTE getAttributeStats(");
appendStringLiteralAH(query, nspnames->data, fout);
appendPQExpBufferStr(query, "::pg_catalog.name[],");
appendStringLiteralAH(query, relnames->data, fout);
appendPQExpBufferStr(query, "::pg_catalog.name[])");
if (fout->remoteVersion >= 190000)
{
appendStringLiteralAH(query, relids->data, fout);
appendPQExpBufferStr(query, "::pg_catalog.oid[])");
}
else
{
appendStringLiteralAH(query, nspnames->data, fout);
appendPQExpBufferStr(query, "::pg_catalog.name[],");
appendStringLiteralAH(query, relnames->data, fout);
appendPQExpBufferStr(query, "::pg_catalog.name[])");
}
res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
destroyPQExpBuffer(query);
}
destroyPQExpBuffer(relids);
destroyPQExpBuffer(nspnames);
destroyPQExpBuffer(relnames);
return res;
@ -11254,8 +11281,14 @@ dumpRelationStats_dumper(Archive *fout, const void *userArg, const TocEntry *te)
query = createPQExpBuffer();
if (!fout->is_prepared[PREPQUERY_GETATTRIBUTESTATS])
{
if (fout->remoteVersion >= 190000)
appendPQExpBufferStr(query,
"PREPARE getAttributeStats(pg_catalog.oid[]) AS\n");
else
appendPQExpBufferStr(query,
"PREPARE getAttributeStats(pg_catalog.name[], pg_catalog.name[]) AS\n");
appendPQExpBufferStr(query,
"PREPARE getAttributeStats(pg_catalog.name[], pg_catalog.name[]) AS\n"
"SELECT s.schemaname, s.tablename, s.attname, s.inherited, "
"s.null_frac, s.avg_width, s.n_distinct, "
"s.most_common_vals, s.most_common_freqs, "
@ -11277,17 +11310,25 @@ dumpRelationStats_dumper(Archive *fout, const void *userArg, const TocEntry *te)
/*
* The results must be in the order of the relations supplied in the
* parameters to ensure we remain in sync as we walk through the TOC.
* The redundant filter clause on s.tablename = ANY(...) seems
* sufficient to convince the planner to use
*
* For v9.4 through v18, the redundant filter clause on s.tablename =
* ANY(...) seems sufficient to convince the planner to use
* pg_class_relname_nsp_index, which avoids a full scan of pg_stats.
* This may not work for all versions.
* In newer versions, pg_stats returns the table OIDs, eliminating the
* need for that hack.
*
* Our query for retrieving statistics for multiple relations uses
* WITH ORDINALITY and multi-argument UNNEST(), both of which were
* introduced in v9.4. For older versions, we resort to gathering
* statistics for a single relation at a time.
*/
if (fout->remoteVersion >= 90400)
if (fout->remoteVersion >= 190000)
appendPQExpBufferStr(query,
"FROM pg_catalog.pg_stats s "
"JOIN unnest($1) WITH ORDINALITY AS u (tableid, ord) "
"ON s.tableid = u.tableid "
"ORDER BY u.ord, s.attname, s.inherited");
else if (fout->remoteVersion >= 90400)
appendPQExpBufferStr(query,
"FROM pg_catalog.pg_stats s "
"JOIN unnest($1, $2) WITH ORDINALITY AS u (schemaname, tablename, ord) "

1
src/bin/pg_dump/pg_dump.h
View file

@ -448,6 +448,7 @@ typedef struct _indexAttachInfo
typedef struct _relStatsInfo
{
DumpableObject dobj;
Oid relid;
int32 relpages;
char *reltuples;
int32 relallvisible;