We are having some performance issues after we upgraded to newest
version of PostgreSQL, before it everything was fast and smooth.
Upgrade was done by pg_upgrade from 9.4 directly do 9.6.1. Now we
upgraded to 9.6.2 with no improvement.
Some information about our setup: Freebsd, Solaris (SmartOS), simple
master-slave using streaming replication.
Problem:
Very high system CPU when master is streaming replication data, CPU
goes up to 77%. Only one process is generating this load, it's a
postgresql startup process. When I attached a truss to this process I
saw a lot o read calls with almost the same number of errors (EAGAIN).
root@d8:~ # truss -c -p 38091
^Csyscall seconds calls errors
semop 0.001611782 198 0
write 0.000074404 2 0
read 2.281535100 17266 12375
openat 0.000683532 48 0
lseek 0.177612479 20443 0
close 0.000395549 48 0
------------- ------- -------
2.461912846 38005 12375
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(444,0x0,SEEK_END) = 32571392 (0x1f10000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(444,0x0,SEEK_END) = 32571392 (0x1f10000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(7,0x0,SEEK_END) = 164487168 (0x9cde000)
lseek(778,0x0,SEEK_END) = 57344 (0xe000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(894,0x0,SEEK_END) = 139296768 (0x84d8000)
lseek(894,0x4b7e000,SEEK_SET) = 79159296 (0x4b7e000)
read(894," ~\0\08\a\M--m\0\0\^A\0\M^T\0000"...,8192) = 8192 (0x2000)
lseek(3,0xfa6000,SEEK_SET) = 16408576 (0xfa6000)
read(3,"\M^S\M-P\^E\0\^A\0\0\0\0`\M-z"...,8192) = 8192 (0x2000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(894,0x0,SEEK_END) = 139296768 (0x84d8000)
lseek(894,0x0,SEEK_END) = 139296768 (0x84d8000)
lseek(894,0x449c000,SEEK_SET) = 71942144 (0x449c000)
read(894,"\^_~\0\0\M-H\M-H\M-B\M-b\0\0\^E"...,8192) = 8192 (0x2000)
lseek(818,0x0,SEEK_END) = 57344 (0xe000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
lseek(442,0x0,SEEK_END) = 10174464 (0x9b4000)
lseek(442,0x4c4000,SEEK_SET) = 4997120 (0x4c4000)
read(442,"\^_~\0\0\M-P\M-+\M-1\M-b\0\0\0\0"...,8192) = 8192 (0x2000)
read(6,0x7fffffffa0c7,1) ERR#35 'Resource temporarily unavailable'
Descriptor 6 is a pipe
Read call try to read one byte over and over, I looked up to source
code and I think this file is responsible for this behavior
src/backend/storage/ipc/latch.c. There was no such file in 9.4.
--
Piotr Gasidło