Re: CREATE INDEX CONCURRENTLY does not index prepared xact's data

On Fri, Jul 30, 2021 at 03:42:10PM +0500, Andrey Borodin wrote:
> > 30 июля 2021 г., в 07:25, Noah Misch <noah(at)leadboat(dot)com> написал(а):
> > What alternative fix designs should we consider?
>
> I observe that provided patch fixes CIC under normal transactions, but test with 2PC still fails similarly.
> Unindexed tuple was committed somewhere at the end of Phase 3 or 4.
> 2021-07-30 15:35:31.806 +05 [25987] 002_cic_2pc.pl LOG: statement: REINDEX INDEX CONCURRENTLY idx;
> 2021-07-30 15:35:31.806 +05 [25987] 002_cic_2pc.pl WARNING: Phase 1
> 2021-07-30 15:35:31.806 +05 [25987] 002_cic_2pc.pl WARNING: Phase 2
> 2021-07-30 15:35:31.806 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6735
> 2021-07-30 15:35:31.807 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6736
> 2021-07-30 15:35:31.808 +05 [25987] 002_cic_2pc.pl WARNING: Phase 3
> 2021-07-30 15:35:31.808 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6750
> 2021-07-30 15:35:31.809 +05 [25987] 002_cic_2pc.pl WARNING: Phase 4
> 2021-07-30 15:35:31.809 +05 [25987] 002_cic_2pc.pl WARNING: Phase 5
> 2021-07-30 15:35:31.809 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6762
> 2021-07-30 15:35:31.809 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6763
> 2021-07-30 15:35:31.810 +05 [25987] 002_cic_2pc.pl WARNING: Phase 6
> 2021-07-30 15:35:31.810 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid 6/2166
> 2021-07-30 15:35:31.810 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6767
> 2021-07-30 15:35:31.810 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6764
> 2021-07-30 15:35:31.810 +05 [25987] 002_cic_2pc.pl WARNING: XXX: VirtualXactLock vxid -1/6765
> 2021-07-30 15:35:31.811 +05 [25987] 002_cic_2pc.pl WARNING: Phase Final
> 2021-07-30 15:35:31.811 +05 [25987] 002_cic_2pc.pl LOG: statement: SELECT bt_index_check('idx',true);
> 2021-07-30 15:35:31.813 +05 [25987] 002_cic_2pc.pl ERROR: heap tuple (46,16) from table "tbl" lacks matching index tuple within index "idx" xmin 6751 xmax 0

I see a failure, too. Once again, "i:" lines are events within the INSERT
backend, and "r:" lines are events within the REINDEX CONCURRENTLY backend:

r: Phase 2 begins.
i: INSERT. Start PREPARE.
r: Phase 2 commits indisready=t for idx_ccnew.
r: Start waiting for the INSERT to finish.
i: PREPARE finishes.
r: Wake up and start validate_index(). This is a problem. It needed to wait
for COMMIT PREPARED to finish.

This may have a different explanation than the failure you saw, because my
INSERT transaction already had a permanent XID before the start of phase 3. I
won't have time to study this further in the next several days. Can you find
out where things go wrong? The next thing I would study is VirtualXactLock(),
specifically what happens if the lock holder is a normal backend (with or
without an XID) when VirtualXactLock() starts but becomes a prepared
transaction (w/ different PGPROC) before VirtualXactLock() ends.