Happened again, another backtrace from a COMMIT process. I changed the commit_delay to 0 (it was 4000 to help with our storage) and will report back.
Already logging to debuglog.txt.
#0 0x00007f47b0789ec7 in semop () from /lib/libc.so.6
#1 0x00007f47b2513d91 in PGSemaphoreLock (sema=0x7f47abfe7ed0, interruptOK=0 '\000') at pg_sema.c:421
#2 0x00007f47b25704f4 in LWLockWaitForVar (l=0x7f449f452680, valptr=0x7f449f4526a0, oldval=<optimized out>, newval=0xffffffffffffffff) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/lmgr/lwlock.c:1011
#3 0x00007f47b23a93e6 in WaitXLogInsertionsToFinish (upto=121780827906336) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:1755
#4 0x00007f47b23aa1d3 in XLogFlush (record=121780827898328) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:2849
#5 0x00007f47b2398f17 in RecordTransactionCommit () at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xact.c:1196
#6 0x00007f47b239921b in CommitTransaction () at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xact.c:1953
#7 0x00007f47b239a8e5 in CommitTransactionCommand () at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xact.c:2732
#8 0x00007f47b257c105 in finish_xact_command () at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/tcop/postgres.c:2437
#9 0x00007f47b2580a10 in exec_execute_message (max_rows=<optimized out>, portal_name=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/tcop/postgres.c:1974
#10 PostgresMain (argc=<optimized out>, argv=<optimized out>, dbname=0x7f47b49b5730 "ifms_db", username=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/tcop/postgres.c:4137
#11 0x00007f47b25280f5 in BackendRun (port=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:4164
#12 BackendStartup (port=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:3829
#13 ServerLoop () at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:1597
#14 PostmasterMain (argc=<optimized out>, argv=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/postmaster/postmaster.c:1244
#15 0x00007f47b24ba474 in main (argc=5, argv=0x7f47b49b4920) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/main/main.c:228
Detaching from program: /usr/lib/postgresql/9.4/bin/postgres, process 15601
On 20 July 2015 at 15:21, Heikki Linnakangas <hlinnaka@xxxxxx> wrote:
A backend always updates its insert position before sleeping/acquiring another lock, by calling WALInsertLockUpdateInsertingAt. So even though another backend might indeed be in the initializedUpto==InvalidXlogRecPtr state, it will get out of that state before either by releasing the lock or updating initializedUpto, before it will in turn do anything that might deadlock.On 07/20/2015 03:01 PM, Andres Freund wrote:
Heikki,
On 2015-07-20 13:27:12 +0200, Andres Freund wrote:
On 2015-07-20 13:22:42 +0200, Andres Freund wrote:
Hm. The problem seems to be the WaitXLogInsertionsToFinish() call in
XLogFlush().
These are the relevant stack traces:
db9lock/debuglog-commit.txt
#2 0x00007f7405bd44f4 in LWLockWaitForVar (l=0x7f70f2ab6680, valptr=0x7f70f2ab66a0, oldval=<optimized out>, newval=0xffffffffffffffff) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/lmgr/lwlock.c:1011
#3 0x00007f7405a0d3e6 in WaitXLogInsertionsToFinish (upto=121713318915952) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:1755
#4 0x00007f7405a0e1d3 in XLogFlush (record=121713318911056) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:2849
db9lock/debuglog-insert-8276.txt
#1 0x00007f7405b77d91 in PGSemaphoreLock (sema=0x7f73ff6531d0, interruptOK=0 '\000') at pg_sema.c:421
#2 0x00007f7405bd4849 in LWLockAcquireCommon (val=<optimized out>, valptr=<optimized out>, mode=<optimized out>, l=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/lmgr/lwlock.c:626
#3 LWLockAcquire (l=0x7f70ecaaa1a0, mode=LW_EXCLUSIVE) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/storage/lmgr/lwlock.c:467
#4 0x00007f7405a0dcca in AdvanceXLInsertBuffer (upto=<optimized out>, opportunistic=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:2161
#5 0x00007f7405a0e301 in GetXLogBuffer (ptr=121713318928384) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:1848
#6 0x00007f7405a0e9c9 in CopyXLogRecordToWAL (EndPos=<optimized out>, StartPos=<optimized out>, rdata=0x7ffff1c21b90, isLogSwitch=<optimized out>, write_len=<optimized out>) at /tmp/buildd/postgresql-9.4-9.4.4/build/../src/backend/access/transam/xlog.c:1494
#7 XLogInsert (rmid=<optimized out>, info=<optimized out>, rdata=<optimized out>) at /tmp/buildd/postgre
XLogFlush() has the following comment:
/*
* Re-check how far we can now flush the WAL. It's generally not
* safe to call WaitXLogInsertionsToFinish while holding
* WALWriteLock, because an in-progress insertion might need to
* also grab WALWriteLock to make progress. But we know that all
* the insertions up to insertpos have already finished, because
* that's what the earlier WaitXLogInsertionsToFinish() returned.
* We're only calling it again to allow insertpos to be moved
* further forward, not to actually wait for anyone.
*/
insertpos = WaitXLogInsertionsToFinish(insertpos);
but I don't think that's valid reasoning. WaitXLogInsertionsToFinish()
calls LWLockWaitForVar(oldval = InvalidXLogRecPtr), which will block if
there's a exlusive locker and some backend doesn't yet have set
initializedUpto. Which seems like a ossible state?
Clearly there's *something* wrong here, though, given the bug report...
- Heikki
