Fix misapplication of pgstat_count_truncate to wrong relation.

The stanza of ExecuteTruncate[Guts] that truncates a target table's toast
relation re-used the loop local variable "rel" to reference the toast rel.
This was safe enough when written, but commit d42358efb added code below
that that supposed "rel" still pointed to the parent table.  Therefore,
the stats counter update was applied to the wrong relcache entry (the
toast rel not the user rel); and if we were unlucky and that relcache
entry had been flushed during reindex_relation, very bad things could
ensue.

(I'm surprised that CLOBBER_CACHE_ALWAYS testing hasn't found this.
I'm even more surprised that the problem wasn't detected during the
development of d42358efb; it must not have been tested in any case
with a toast table, as the incorrect stats counts are very obvious.)

To fix, replace use of "rel" in that code branch with a more local
variable.  Adjust test cases added by d42358efb so that some of them
use tables with toast tables.

Per bug #15540 from Pan Bian.  Back-patch to 9.5 where d42358efb came in.

Discussion: https://postgr.es/m/15540-01078812338195c0@postgresql.org

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 1894485901d33aff3e914fd5a5d4f3c67f145990..bc83a9a4a0709481575b2953eb9cd2db81c1db3d 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1225,19 +1225,22 @@ ExecuteTruncate(TruncateStmt *stmt)
                                heap_create_init_fork(rel);
 
                        heap_relid = RelationGetRelid(rel);
-                       toast_relid = rel->rd_rel->reltoastrelid;
 
                        /*
                         * The same for the toast table, if any.
                         */
+                       toast_relid = rel->rd_rel->reltoastrelid;
                        if (OidIsValid(toast_relid))
                        {
-                               rel = relation_open(toast_relid, AccessExclusiveLock);
-                               RelationSetNewRelfilenode(rel, rel->rd_rel->relpersistence,
+                               Relation        toastrel = relation_open(toast_relid,
+                                                                                                        AccessExclusiveLock);
+
+                               RelationSetNewRelfilenode(toastrel,
+                                                                                 toastrel->rd_rel->relpersistence,
                                                                                  RecentXmin, minmulti);
-                               if (rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
-                                       heap_create_init_fork(rel);
-                               heap_close(rel, NoLock);
+                               if (toastrel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
+                                       heap_create_init_fork(toastrel);
+                               heap_close(toastrel, NoLock);
                        }
 
                        /*

diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 4f397a32804df5289a8c6cd6e14f52a29f6039ff..2a1d1e24ac67b17e594bff6f2a13b6cd18403795 100644 (file)
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -80,9 +80,9 @@ end
 $$ language plpgsql;
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
-CREATE TABLE trunc_stats_test1(id serial);
+CREATE TABLE trunc_stats_test1(id serial, stuff text);
 CREATE TABLE trunc_stats_test2(id serial);
-CREATE TABLE trunc_stats_test3(id serial);
+CREATE TABLE trunc_stats_test3(id serial, stuff text);
 CREATE TABLE trunc_stats_test4(id serial);
 -- check that n_live_tup is reset to 0 after truncate
 INSERT INTO trunc_stats_test DEFAULT VALUES;

diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 521dc4d6a3462758e821e4c4b62023ded7bc902c..bb116185c757c82706905679f8c765f921908751 100644 (file)
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -76,9 +76,9 @@ $$ language plpgsql;
 
 -- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
 CREATE TABLE trunc_stats_test(id serial);
-CREATE TABLE trunc_stats_test1(id serial);
+CREATE TABLE trunc_stats_test1(id serial, stuff text);
 CREATE TABLE trunc_stats_test2(id serial);
-CREATE TABLE trunc_stats_test3(id serial);
+CREATE TABLE trunc_stats_test3(id serial, stuff text);
 CREATE TABLE trunc_stats_test4(id serial);
 
 -- check that n_live_tup is reset to 0 after truncate