Re: Wait free LW_SHARED acquisition - v0.9

On Thu, Oct 30, 2014 at 5:52 PM, Andres Freund <andres(at)2ndquadrant(dot)com>
wrote:
>
> On 2014-10-21 12:40:56 +0530, Amit Kapila wrote:
> > While doing performance tests, I noticed a hang at higher client
> > counts with patch. I have tried to check call stack for few of
> > processes and it is as below:
> >
> > #0 0x0000008010933e54 in .semop () from /lib64/libc.so.6
> > #1 0x0000000010286e48 in .PGSemaphoreLock ()
> > #2 0x00000000102f68bc in .LWLockAcquire ()
> > #3 0x00000000102d1ca0 in .ReadBuffer_common ()
> > #4 0x00000000102d2ae0 in .ReadBufferExtended ()
> > #5 0x00000000100a57d8 in ._bt_getbuf ()
> > #6 0x00000000100a6210 in ._bt_getroot ()
> > #7 0x00000000100aa910 in ._bt_search ()
> > #8 0x00000000100ab494 in ._bt_first ()
> > #9 0x00000000100a8e84 in .btgettuple ()
> > ..
> >
> > #0 0x0000008010933e54 in .semop () from /lib64/libc.so.6
> > #1 0x0000000010286e48 in .PGSemaphoreLock ()
> > #2 0x00000000102f68bc in .LWLockAcquire ()
> > #3 0x00000000102d1ca0 in .ReadBuffer_common ()
> > #4 0x00000000102d2ae0 in .ReadBufferExtended ()
> > #5 0x00000000100a57d8 in ._bt_getbuf ()
> > #6 0x00000000100a6210 in ._bt_getroot ()
> > #7 0x00000000100aa910 in ._bt_search ()
> > #8 0x00000000100ab494 in ._bt_first ()
> > ...
> >
> > The test configuration is as below:
> > Test env - Power - 7 (hydra)
> > scale_factor - 3000
> > shared_buffers - 8GB
> > test mode - pgbench read only
> >
> > test execution -
> > ./pgbench -c 128 -j 128 -T 1800 -S -M prepared postgres
> >
> > I have ran it for half an hour, but it doesn't came out even after
> > ~2 hours. It doesn't get reproduced every time, currently I am
> > able to reproduce it and the m/c is in same state, if you want any
> > info, let me know (unfortunately binaries are in release mode, so
> > might not get enough information).
>
> Hm. What commit did you apply the series ontop? I managed to reproduce a
> hang, but it was just something that heikki had already fixed...
>

commit 494affbd900d1c90de17414a575af1a085c3e37a
Author: Noah Misch <noah(at)leadboat(dot)com>
Date: Sun Oct 12 23:33:37 2014 -0400

And, I think you are saying that heikki's commit e0d97d has fixed
this issue, in that case I will check once by including that fix?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com