postgres.git / summary / log / commit / refs

commit    a295684b89143bc4bf51e1b40eb195de35570feb
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Oct 16 18:06:12 2023 +0000

    Ensure we have a snapshot while dropping ON COMMIT DROP temp tables.
    
    Dropping a temp table could entail TOAST table access to clean out
    toasted catalog entries, such as large pg_constraint.conbin strings
    for complex CHECK constraints.  If we did that via ON COMMIT DROP,
    we triggered the assertion in init_toast_snapshot(), because
    there was no provision for setting up a snapshot for the drop
    actions.  Fix that.
    
    (I assume here that the adjacent truncation actions for ON COMMIT
    DELETE ROWS don't have a similar problem: it doesn't seem like
    nontransactional truncations would need to touch any toasted fields.
    If that proves wrong, we could refactor a bit to have the same
    snapshot acquisition cover that too.)
    
    The test case added here does not fail before v15, because that
    assertion was added in 277692220 which was not back-patched.
    However, the race condition the assertion warns of surely
    exists further back, so back-patch to all supported branches.
    
    Per report from Richard Guo.
    
    Discussion: https://postgr.es/m/CAMbWs4-x26=_QxxgdJyNbiCDzvtr2WV5ZDso_v-CukKEe6cBZw@mail.gmail.com


 src/backend/commands/tablecmds.c   |  8 ++++++++
 src/test/regress/expected/temp.out | 20 ++++++++++++++++++++
 src/test/regress/sql/temp.sql      | 16 ++++++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 385616bdb54..b13dd19f555 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -14331,6 +14331,12 @@ PreCommit_on_commit_actions(void)
 			add_exact_object_address(&object, targetObjects);
 		}
 
+		/*
+		 * Object deletion might involve toast table access (to clean up
+		 * toasted catalog entries), so ensure we have a valid snapshot.
+		 */
+		PushActiveSnapshot(GetTransactionSnapshot());
+
 		/*
 		 * Since this is an automatic drop, rather than one directly initiated
 		 * by the user, we pass the PERFORM_DELETION_INTERNAL flag.
@@ -14338,6 +14344,8 @@ PreCommit_on_commit_actions(void)
 		performMultipleDeletions(targetObjects, DROP_CASCADE,
 								 PERFORM_DELETION_INTERNAL | PERFORM_DELETION_QUIETLY);
 
+		PopActiveSnapshot();
+
 #ifdef USE_ASSERT_CHECKING
 
 		/*
diff --git a/src/test/regress/expected/temp.out b/src/test/regress/expected/temp.out
index 5fa20a05bfe..981f7649779 100644
--- a/src/test/regress/expected/temp.out
+++ b/src/test/regress/expected/temp.out
@@ -108,6 +108,26 @@ SELECT * FROM temptest;
    1
 (1 row)
 
+COMMIT;
+SELECT * FROM temptest;
+ERROR:  relation "temptest" does not exist
+LINE 1: SELECT * FROM temptest;
+                      ^
+-- Test it with a CHECK condition that produces a toasted pg_constraint entry
+BEGIN;
+do $$
+begin
+  execute format($cmd$
+    CREATE TEMP TABLE temptest (col text CHECK (col < %L)) ON COMMIT DROP
+  $cmd$,
+    (SELECT string_agg(g.i::text || ':' || random()::text, '|')
+     FROM generate_series(1, 100) g(i)));
+end$$;
+SELECT * FROM temptest;
+ col 
+-----
+(0 rows)
+
 COMMIT;
 SELECT * FROM temptest;
 ERROR:  relation "temptest" does not exist
diff --git a/src/test/regress/sql/temp.sql b/src/test/regress/sql/temp.sql
index fdef2b0f978..9414fb63361 100644
--- a/src/test/regress/sql/temp.sql
+++ b/src/test/regress/sql/temp.sql
@@ -101,6 +101,22 @@ COMMIT;
 
 SELECT * FROM temptest;
 
+-- Test it with a CHECK condition that produces a toasted pg_constraint entry
+BEGIN;
+do $$
+begin
+  execute format($cmd$
+    CREATE TEMP TABLE temptest (col text CHECK (col < %L)) ON COMMIT DROP
+  $cmd$,
+    (SELECT string_agg(g.i::text || ':' || random()::text, '|')
+     FROM generate_series(1, 100) g(i)));
+end$$;
+
+SELECT * FROM temptest;
+COMMIT;
+
+SELECT * FROM temptest;
+
 -- ON COMMIT is only allowed for TEMP
 
 CREATE TABLE temptest(col int) ON COMMIT DELETE ROWS;


[parent: f1634c968101]