Re: SR standby hangs

Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> This has happened again. This time we have some debug info available,
> and can possible get more, if people tell me what will be helpful:

> (gdb) f 2
> #2 0x00000000005de735 in LockBufferForCleanup (buffer=310163) at
> bufmgr.c:2432
> 2432 ProcWaitForSignal();
> (gdb) p *bufHdr
> $2 = {tag = {rnode = {spcNode = 16393, dbNode = 40475, relNode =
> 41880}, forkNum = MAIN_FORKNUM, blockNum = 18913}, flags = 6,
> usage_count = 1, refcount = 1, wait_backend_pid = 9111,
> buf_hdr_lock = 0 '\000', buf_id = 310162, freeNext = -2,
> io_in_progress_lock = 620448, content_lock = 620449}

Well, that's pretty interesting: refcount is only 1, and the
BM_PIN_COUNT_WAITER flag is not set. AFAICS this *must* mean that the
buffer had been pinned and whoever had it (presumably bgwriter) did
UnpinBuffer(). So it appears that the signal just plain got lost :-(,
which suggests a kernel bug. What platform is this on, again?

> Strangely, I don't even see ProcWaitForSignal() in the frame list - I
> shouldn't have thought it was a candidate to be optimised away.

It has a tail call to PGSemaphoreLock, so not totally surprising.

regards, tom lane