From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Further refine _SPI_execute_plan's rule for atomic execution.
Date: Wed, 16 Oct 2024 21:36:47 +0000
Message-ID: <E1t1BhH-00192i-QM@gemulon.postgresql.org> (raw)
Further refine _SPI_execute_plan's rule for atomic execution.
Commit 2dc1deaea turns out to have been still a brick shy of a load,
because CALL statements executing within a plpgsql exception block
could still pass the wrong snapshot to stable functions within the
CALL's argument list. That happened because standard_ProcessUtility
forces isAtomicContext to true if IsTransactionBlock is true, which
it always will be inside a subtransaction. Then ExecuteCallStmt
would think it does not need to push a new snapshot --- but
_SPI_execute_plan didn't do so either, since it thought it was in
nonatomic mode.
The best fix for this seems to be for _SPI_execute_plan to operate
in atomic execution mode if IsSubTransaction() is true, even when the
SPI context as a whole is non-atomic. This makes _SPI_execute_plan
have the same rules about when non-atomic execution is allowed as
_SPI_commit/_SPI_rollback have about when COMMIT/ROLLBACK are allowed,
which seems appropriately symmetric. (If anyone ever tries to allow
COMMIT/ROLLBACK inside a subtransaction, this would all need to be
rethought ... but I'm unconvinced that such a thing could be logically
consistent at all.)
For further consistency, also check IsSubTransaction() in
SPI_inside_nonatomic_context. That does not matter for its
one present-day caller StartTransaction, which can't be reached
inside a subtransaction. But if any other callers ever arise,
they'd presumably want this definition.
Per bug #18656 from Alexander Alehin. Back-patch to all
supported branches, like previous fixes in this area.
Discussion: https://postgr.es/m/18656-cade1780866ef66c@postgresql.org
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/25d639eea04300e8bc7bc8258a07e19b13dfb1f3
Modified Files
--------------
src/backend/executor/spi.c | 14 ++++++++++----
src/pl/plpgsql/src/expected/plpgsql_call.out | 20 ++++++++++++++++++++
src/pl/plpgsql/src/sql/plpgsql_call.sql | 17 +++++++++++++++++
3 files changed, 47 insertions(+), 4 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Further refine _SPI_execute_plan's rule for atomic execution.
In-Reply-To: <E1t1BhH-00192i-QM@gemulon.postgresql.org>
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