From 751162fb6701d84747c753457a995833ff8313bb Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Fri, 13 Nov 2026 15:43:23 -0500 Subject: [PATCH v1] Fix pgstattuple_approx handling of unknown tuple estimates vac_estimate_reltuples() can return -1 when there is not enough information to estimate the number of live tuples. pgstattuple_approx() assigned that value to an unsigned counter before attempting to clamp it, making the clamp ineffective and exposing -1 through the bigint result. Clamp the signed estimate before assigning it to the unsigned counter. Reported-by: Zsolt Parragi Author: Melanie Plageman Discussion: https://postgr.es/m/CAN4CZFM0y8t%2BAQ8PWTeuBXnFtRDUNvkfVzzA_yo6uJ2bceK%3DxA%40mail.gmail.com Backpatch-through: 15 --- contrib/pgstattuple/expected/pgstattuple.out | 12 ++++++++++++ contrib/pgstattuple/pgstatapprox.c | 11 ++++++----- contrib/pgstattuple/sql/pgstattuple.sql | 10 ++++++++++ doc/src/sgml/pgstattuple.sgml | 3 ++- 4 files changed, 30 insertions(+), 6 deletions(-) diff --git a/contrib/pgstattuple/expected/pgstattuple.out b/contrib/pgstattuple/expected/pgstattuple.out index 9176dc98b6a..32f055b2d53 100644 --- a/contrib/pgstattuple/expected/pgstattuple.out +++ b/contrib/pgstattuple/expected/pgstattuple.out @@ -250,6 +250,18 @@ select pg_relpages((select reltoastrelid from pg_class where relname = 'test')); 0 (1 row) +-- An unknown approximate tuple count is reported as zero. +begin; +create temp table test_approx_unknown (id int); +copy test_approx_unknown from stdin with (freeze); +commit; +select scanned_percent, approx_tuple_count + from pgstattuple_approx('test_approx_unknown'); + scanned_percent | approx_tuple_count +-----------------+-------------------- + 0 | 0 +(1 row) + -- not for the index calls though, of course select pgstatindex('test_partition'); ERROR: relation "test_partition" is not a btree index diff --git a/contrib/pgstattuple/pgstatapprox.c b/contrib/pgstattuple/pgstatapprox.c index bed904206d7..8fd5e8d877e 100644 --- a/contrib/pgstattuple/pgstatapprox.c +++ b/contrib/pgstattuple/pgstatapprox.c @@ -119,6 +119,7 @@ statapprox_heap(Relation rel, output_type *stat) { BlockNumber nblocks; BufferAccessStrategy bstrategy; + double estimated_tuple_count; TransactionId OldestXmin; StatApproxReadStreamPrivate p; ReadStream *stream; @@ -254,12 +255,12 @@ statapprox_heap(Relation rel, output_type *stat) * tuples in all-visible pages, so no correction is needed for that, and * we already accounted for the space in those pages, too. */ - stat->tuple_count = vac_estimate_reltuples(rel, nblocks, p.scanned, - p.scanned_new, - stat->tuple_count); + estimated_tuple_count = vac_estimate_reltuples(rel, nblocks, p.scanned, + p.scanned_new, + stat->tuple_count); - /* It's not clear if we could get -1 here, but be safe. */ - stat->tuple_count = Max(stat->tuple_count, 0); + /* Report zero when there is not enough information for an estimate. */ + stat->tuple_count = Max(estimated_tuple_count, 0); /* * Calculate percentages if the relation has one or more pages. diff --git a/contrib/pgstattuple/sql/pgstattuple.sql b/contrib/pgstattuple/sql/pgstattuple.sql index 7e72c567a06..0853a23c985 100644 --- a/contrib/pgstattuple/sql/pgstattuple.sql +++ b/contrib/pgstattuple/sql/pgstattuple.sql @@ -107,6 +107,16 @@ select pgstattuple((select reltoastrelid from pg_class where relname = 'test')); select pgstattuple_approx((select reltoastrelid from pg_class where relname = 'test')); select pg_relpages((select reltoastrelid from pg_class where relname = 'test')); +-- An unknown approximate tuple count is reported as zero. +begin; +create temp table test_approx_unknown (id int); +copy test_approx_unknown from stdin with (freeze); +1 +\. +commit; +select scanned_percent, approx_tuple_count + from pgstattuple_approx('test_approx_unknown'); + -- not for the index calls though, of course select pgstatindex('test_partition'); select pgstatginindex('test_partition'); diff --git a/doc/src/sgml/pgstattuple.sgml b/doc/src/sgml/pgstattuple.sgml index 54d8f90245e..8828f4f1272 100644 --- a/doc/src/sgml/pgstattuple.sgml +++ b/doc/src/sgml/pgstattuple.sgml @@ -572,7 +572,8 @@ approx_free_percent | 2.09 approx_tuple_count bigint - Number of live tuples (estimated) + Number of live tuples (estimated), or zero if there is not + enough information to estimate it approx_tuple_len -- 2.43.0