On Wed, Dec 18, 2019 at 4:53 AM James(王旭) <wan...@gu360.com> wrote:
> Hello, >> >> I encountered into this kernel message, and I cannot login into the Linux >> system anymore: > > >> >> Dec 17 23:01:50 hq-pg kernel: sh (6563): drop_caches: 1 >> >> Dec 17 23:02:30 hq-pg kernel: INFO: task sync:6573 blocked for more than >>> 120 seconds. >> >> Dec 17 23:02:30 hq-pg kernel: "echo 0 > >>> /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> >> Dec 17 23:02:30 hq-pg kernel: sync D ffff965ebabd1040 0 >>> 6573 6572 0x00000080 >> >> Dec 17 23:02:30 hq-pg kernel: Call Trace: >> >> Dec 17 23:02:30 hq-pg kernel: [<ffffffffa48760a0>] ? >>> generic_write_sync+0x70/0x70 >> >> >> After some google I guess it's the problem that IO speed is low, while >> the insert requests are coming too much quickly.So PG put these into cache >> first then kernel called sync > > Could you expand on what you found in the googling, with links? I've never seen these in my kernel log, and I don't know what they mean other than the obvious that it is something to do with IO. Also, what kernel and file system are you using? > . > > I know I can queue the requests, so that POSTGRES will not accept these >> requests which will result in an increase in system cache. > > But is there any way I can tell POSTGRES, that you can only handle 20000 >> records per second, or 4M per second, please don't accept inserts more than >> that speed. > > For me, POSTGRES just waiting is much better than current behavior. > > I don't believe there is a setting from within PostgreSQL to do this. There was a proposal for a throttle on WAL generation back in February, but with no recent discussion or (visible) progress: https://www.postgresql.org/message-id/flat/2B42AB02-03FC-406B-B92B-18DED2D8D491%40anarazel.de#b63131617e84d3a0ac29da956e6b8c5f I think the real answer here to get a better IO system, or maybe a better kernel. Otherwise, once you find a painful workaround for one symptom you will just smack into another one. Cheers, Jeff >
