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Introduce GUC_NO_RESET flag.

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Previously, the transaction-property GUCs such as transaction_isolation
could be reset after starting a transaction, because we marked them
as GUC_NO_RESET_ALL but still allowed a targeted RESET.  That leads to
assertion failures or worse, because those properties aren't supposed
to change after we've acquired a transaction snapshot.

There are some NO_RESET_ALL variables for which RESET is okay, so
we can't just redefine the semantics of that flag.  Instead introduce
a separate GUC_NO_RESET flag.  Mark "seed", as well as the transaction
property GUCs, as GUC_NO_RESET.

We have to disallow GUC_ACTION_SAVE as well as straight RESET, because
otherwise a function having a "SET transaction_isolation" clause can
still break things: the end-of-function restore action is equivalent
to a RESET.

No back-patch, as it's conceivable that someone is doing something
this patch will forbid (like resetting one of these GUCs at transaction
start, or "CREATE FUNCTION ... SET transaction_read_only = 1") and not
running into problems with it today.  Given how long we've had this
issue and not noticed, the side effects in non-assert builds can't be
too serious.

Per bug #17385 from Andrew Bille.

Masahiko Sawada

Discussion: https://postgr.es/m/17385-9ee529fb091f0ce5@postgresql.org
This commit is contained in:
Tom Lane
2022-09-27 11:47:12 -04:00
parent 4148c8b3da
commit 3853664265
11 changed files with 103 additions and 13 deletions
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5
src/pl/plpgsql/src/expected/plpgsql_transaction.out
View File

@ -576,8 +576,7 @@ BEGIN
PERFORM 1;
RAISE INFO '%', current_setting('transaction_isolation');
COMMIT;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
RESET TRANSACTION ISOLATION LEVEL;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
PERFORM 1;
RAISE INFO '%', current_setting('transaction_isolation');
COMMIT;
@ -585,7 +584,7 @@ END;
$$;
INFO: read committed
INFO: repeatable read
INFO: read committed
INFO: serializable
-- error cases
DO LANGUAGE plpgsql $$
BEGIN

3
src/pl/plpgsql/src/sql/plpgsql_transaction.sql
View File

@ -481,8 +481,7 @@ BEGIN
PERFORM 1;
RAISE INFO '%', current_setting('transaction_isolation');
COMMIT;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
RESET TRANSACTION ISOLATION LEVEL;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
PERFORM 1;
RAISE INFO '%', current_setting('transaction_isolation');
COMMIT;