From: Сурен Арустамян <suren-a@inbox.ru>
To: pgsql-performance@postgresql.org
Subject: SELECT outage in semop
Date: Fri, 30 May 2014 18:55:13 +0400
Message-ID: <1401461713.227724134@f426.i.mail.ru> (raw)
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Hi all,
I'm using postgresql 9.3.4 on Red Hat Enterprise Linux Server release 6.5 (Santiago)
Linux 193-45-142-74 2.6.32-431.17.1.el6.x86_64 #1 SMP Fri Apr 11 17:27:00 EDT 2014 x86_64 x86_64 x86_64 GNU/Linux Server specs:
4x Intel(R) Xeon(R) CPU E7- 4870 @ 2.40GHz (40 physical cores in total)
441 GB of RAM I have a schema when multi process daemon is setted up on the system and each process holds 1 postgresql session.
Each process of this daemon run readonly queries over the database.
In normal situation it at most 35 ms for queries but from time to time (at a random point of time) each database session hanges in some very strange semop call. Here is a part of the strace:
41733 20:15:09.682186 lseek(41, 0, SEEK_END) = 16384 <0.000007>
41733 20:15:09.682218 lseek(42, 0, SEEK_END) = 16384 <0.000008>
41733 20:15:09.682258 lseek(43, 0, SEEK_END) = 8192 <0.000007>
41733 20:15:09.682290 lseek(44, 0, SEEK_END) = 16384 <0.000007>
41733 20:15:09.682365 brk(0x1a79000) = 0x1a79000 <0.000010>
41733 20:15:09.682507 semop(393228, {{0, -1, 0}}, 1) = 0 <2.080439>
41733 20:15:11.769030 brk(0x1b79000) = 0x1b79000 <0.000028>
41733 20:15:11.774384 lseek(20, 0, SEEK_END) = 81920 <0.000032>
41733 20:15:11.774591 lseek(35, 0, SEEK_END) = 98263040 <0.000084>
41733 20:15:11.775000 brk(0x1b9b000) = 0x1b9b000 <0.000021>
41733 20:15:11.775741 lseek(35, 0, SEEK_END) = 98263040 <0.000056>
41733 20:15:11.776763 brk(0x19b9000) = 0x19b9000 <0.000329>
41733 20:15:11.777195 sendto(9,
41733 20:45:58.300097 lseek(39, 0, SEEK_END) = 32768 <0.000015>
41733 20:45:58.300167 lseek(40, 0, SEEK_END) = 32768 <0.000015>
41733 20:45:58.300244 lseek(41, 0, SEEK_END) = 16384 <0.000015>
41733 20:45:58.300314 lseek(42, 0, SEEK_END) = 16384 <0.000015>
41733 20:45:58.300384 lseek(43, 0, SEEK_END) = 8192 <0.000014>
41733 20:45:58.300452 lseek(44, 0, SEEK_END) = 16384 <0.000015>
41733 20:45:58.300599 brk(0x1a79000) = 0x1a79000 <0.000020>
41733 20:45:58.306472 brk(0x1b79000) = 0x1b79000 <0.000024>
41733 20:45:58.311412 lseek(20, 0, SEEK_END) = 81920 <0.000026>
41733 20:45:58.311649 lseek(35, 0, SEEK_END) = 98263040 <0.000022>
41733 20:45:58.312049 brk(0x1b9f000) = 0x1b9f000 <0.000021>
41733 20:45:58.312502 lseek(35, 0, SEEK_END) = 98263040 <0.000024>41733 20:45:58.313207 brk(0x19b9000) = 0x19b9000 <0.000243>
41733 20:45:58.313544 sendto(10,
You may see that semop took 2 seconds from the whole system call.
Same semops could be find in other database sessions.
Could you point me how can i find
Best Regards,
Suren Arustamyan
suren-a@inbox.ru
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