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Commita295684

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Ensure we have a snapshot while dropping ON COMMIT DROP temp tables.
Dropping a temp table could entail TOAST table access to clean outtoasted catalog entries, such as large pg_constraint.conbin stringsfor complex CHECK constraints. If we did that via ON COMMIT DROP,we triggered the assertion in init_toast_snapshot(), becausethere was no provision for setting up a snapshot for the dropactions. Fix that.(I assume here that the adjacent truncation actions for ON COMMITDELETE ROWS don't have a similar problem: it doesn't seem likenontransactional truncations would need to touch any toasted fields.If that proves wrong, we could refactor a bit to have the samesnapshot acquisition cover that too.)The test case added here does not fail before v15, because thatassertion was added in2776922 which was not back-patched.However, the race condition the assertion warns of surelyexists 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
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‎src/backend/commands/tablecmds.c

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@@ -14331,13 +14331,21 @@ PreCommit_on_commit_actions(void)
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add_exact_object_address(&object, targetObjects);
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}
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/*
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* Object deletion might involve toast table access (to clean up
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* toasted catalog entries), so ensure we have a valid snapshot.
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*/
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PushActiveSnapshot(GetTransactionSnapshot());
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/*
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* Since this is an automatic drop, rather than one directly initiated
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* by the user, we pass the PERFORM_DELETION_INTERNAL flag.
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*/
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performMultipleDeletions(targetObjects, DROP_CASCADE,
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PERFORM_DELETION_INTERNAL | PERFORM_DELETION_QUIETLY);
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PopActiveSnapshot();
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#ifdef USE_ASSERT_CHECKING
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/*

‎src/test/regress/expected/temp.out

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@@ -108,6 +108,26 @@ SELECT * FROM temptest;
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1
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(1 row)
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COMMIT;
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SELECT * FROM temptest;
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ERROR: relation "temptest" does not exist
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LINE 1: SELECT * FROM temptest;
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^
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-- Test it with a CHECK condition that produces a toasted pg_constraint entry
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BEGIN;
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do $$
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begin
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execute format($cmd$
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CREATE TEMP TABLE temptest (col text CHECK (col < %L)) ON COMMIT DROP
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$cmd$,
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(SELECT string_agg(g.i::text || ':' || random()::text, '|')
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FROM generate_series(1, 100) g(i)));
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end$$;
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SELECT * FROM temptest;
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col
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-----
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(0 rows)
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COMMIT;
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SELECT * FROM temptest;
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ERROR: relation "temptest" does not exist

‎src/test/regress/sql/temp.sql

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@@ -101,6 +101,22 @@ COMMIT;
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SELECT*FROM temptest;
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-- Test it with a CHECK condition that produces a toasted pg_constraint entry
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BEGIN;
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do $$
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begin
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execute format($cmd$
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CREATE TEMP TABLE temptest (coltextCHECK (col< %L))ONCOMMIT DROP
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$cmd$,
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(SELECT string_agg(g.i::text||':'|| random()::text,'|')
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FROM generate_series(1,100) g(i)));
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end$$;
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SELECT*FROM temptest;
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COMMIT;
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SELECT*FROM temptest;
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-- ON COMMIT is only allowed for TEMP
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CREATETABLEtemptest(colint)ONCOMMITDELETE ROWS;

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