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Fix deadlock hazard in CREATE INDEX CONCURRENTLY

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Multiple sessions doing CREATE INDEX CONCURRENTLY simultaneously are
supposed to be able to work in parallel, as evidenced by fixes in commit
c3d09b3bd2 specifically to support this case.  In reality, one of the
sessions would be aborted by a misterious "deadlock detected" error.

Jeff Janes diagnosed that this is because of leftover snapshots used for
system catalog scans -- this was broken by 8aa3e47510 keeping track of
(registering) the catalog snapshot.  To fix the deadlocks, it's enough
to de-register that snapshot prior to waiting.

Backpatch to 9.4, which introduced MVCC catalog scans.

Include an isolationtester spec that 8 out of 10 times reproduces the
deadlock with the unpatched code for me (Álvaro).

Author: Jeff Janes
Diagnosed-by: Jeff Janes
Reported-by: Jeremy Finzel
Discussion: https://postgr.es/m/CAMa1XUhHjCv8Qkx0WOr1Mpm_R4qxN26EibwCrj0Oor2YBUFUTg%40mail.gmail.com
This commit is contained in:
Alvaro Herrera
2018-01-02 19:16:16 -03:00
parent 438036264a
commit 54eff5311d
4 changed files with 63 additions and 0 deletions
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3
src/backend/commands/indexcmds.c
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@ -856,11 +856,14 @@ DefineIndex(Oid relationId,
* doing CREATE INDEX CONCURRENTLY, which would see our snapshot as one
* they must wait for. But first, save the snapshot's xmin to use as
* limitXmin for GetCurrentVirtualXIDs().
*
* Our catalog snapshot could have the same effect, so drop that one too.
*/
limitXmin = snapshot->xmin;
PopActiveSnapshot();
UnregisterSnapshot(snapshot);
InvalidateCatalogSnapshot();
/*
* The index is now valid in the sense that it contains all currently