pgsql: Ensure we have a snapshot while dropping ON COMMIT DROP temp tab - Mailing list pgsql-committers

From Tom Lane
Subject pgsql: Ensure we have a snapshot while dropping ON COMMIT DROP temp tab
Date
Msg-id E1qsRzK-000sVs-GC@gemulon.postgresql.org
Whole thread Raw
List pgsql-committers
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

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/07eb22a7761f88a826c1d561c41aaeace23d3f7f

Modified Files
--------------
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(+)


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