Fix FOR UPDATE NOWAIT on updated tuple chains

Enterprise / PostgreSQL - Alvaro Herrera [alvh.no-ip.org] - 27 August 2014 18:15 UTC

If SELECT FOR UPDATE NOWAIT tries to lock a tuple that is concurrently being updated, it might fail to honor its NOWAIT specification and block instead of raising an error.

Fix by adding a no-wait flag to EvalPlanQualFetch which it can pass down to heap_lock_tuple; also use it in EvalPlanQualFetch itself to avoid blocking while waiting for a concurrent transaction.

Authors: Craig Ringer and Thomas Munro, tweaked by Álvaro http://www.postgresql.org/message-id/51FB6703.9090801@2ndquadrant.com

Per Thomas Munro in the course of his SKIP LOCKED feature submission, who also provided one of the isolation test specs.

Backpatch to 9.4, because that's as far back as it applies without conflicts (although the bug goes all the way back). To that branch also backpatch Thomas Munro's new NOWAIT test cases, committed in master by Heikki as commit 9ee16b49f0aac819bd4823d9b94485ef608b34e8 .

1c9701c Fix FOR UPDATE NOWAIT on updated tuple chains
src/backend/executor/execMain.c | 24 ++++++++----
src/backend/executor/nodeLockRows.c | 2 +-
src/include/executor/executor.h | 2 +-
src/test/isolation/expected/nowait-4.out | 19 ++++++++++
src/test/isolation/expected/nowait-4_1.out | 19 ++++++++++
src/test/isolation/expected/nowait-5.out | 37 ++++++++++++++++++
src/test/isolation/isolation_schedule | 8 ++--
src/test/isolation/specs/nowait-4.spec | 30 +++++++++++++++
src/test/isolation/specs/nowait-5.spec | 57 ++++++++++++++++++++++++++++
9 files changed, 186 insertions(+), 12 deletions(-)

Upstream: git.postgresql.org


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