Re: BUG #13657: Some kind of undetected deadlock between query and "startup process" on replica.

>
>
> So wal replay got AccessExclusiveLock on relation 17987 and waiting for
> something.
> And query waiting for AccessShareLock on the same relation.
>
>
​gdb backtrace from stuck startup process:

(gdb) bt
#0 0x00007f04ad862633 in select () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x00007f04af86488e in pg_usleep (microsec=<optimized out>) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/port/pgsleep.c:53
#2 0x00007f04af7328ac in WaitExceedsMaxStandbyDelay () at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/ipc/standby.c:171
#3 ResolveRecoveryConflictWithVirtualXIDs
(reason=PROCSIG_RECOVERY_CONFLICT_SNAPSHOT, waitlist=0x7f04b13ba2f0) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/ipc/standby.c:232
#4 ResolveRecoveryConflictWithVirtualXIDs (waitlist=0x7f04b13ba2f0,
reason=PROCSIG_RECOVERY_CONFLICT_SNAPSHOT) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/ipc/standby.c:191
#5 0x00007f04af544445 in heap_xlog_clean (record=0x7f04b1395b80,
lsn=107351881751648) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/heap/heapam.c:7329
#6 heap2_redo (lsn=107351881751648, record=0x7f04b1395b80) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/heap/heapam.c:8488
#7 0x00007f04af580648 in StartupXLOG () at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:6920
#8 0x00007f04af6f5d8f in StartupProcessMain () at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/startup.c:224
#9 0x00007f04af58c579 in AuxiliaryProcessMain (argc=2, argv=<optimized
out>) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/bootstrap/bootstrap.c:422
#10 0x00007f04af6f235b in StartChildProcess (type=StartupProcess) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:5155
#11 0x00007f04af6f4847 in PostmasterMain (argc=<optimized out>,
argv=<optimized out>) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:1237
#12 0x00007f04af513a5d in main (argc=5, argv=0x7f04b13731a0) at
/tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/main/main.c:228
​

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