Re: [PERFORM] Problems with pg_locks explosion
It's now running as expected, I made a few other tweaks to get it to an operational state again. So just for closure on this dark period below some notes. There was two triggers that caused the almost instant backlog of locks. As suspected the one was scheduler that caused endless problems whenever it started migrating tasks. This would lock up the database (and server) for a second or more after which a few thousand locks existed. Setting the kernel.sched_migration_cost to 5ms didn't have the desired effect. The scheduler would still stop the world and break down for a few seconds. After much anguish and research (this is a pretty good explanation of the scheduler tunables http://events.linuxfoundation.org/slides/2011/linuxcon/lcna2011_rajan.pdf) I adjusted : sysctl -w kernel.sched_min_granularity_ns=900 sysctl -w kernel.sched_wakeup_granularity_ns=1200 Since then I haven't had an interruption from migration. I also switched hugepage to not be as aggressive, it was also intrusive and my Postgres not configured to use it. "echo madvise > /sys/kernel/mm/transparent_hugepage/defrag" After these changes things started smoothing out and running like it should. I also found that if you are running on striped EBS volumes you should really try and get them busy to get consistent performance. I checked with Amazon and the usage I see on the individual modules were correct. (Not the RAID figure but the numbers on the individual volumes, they were idling) Thanks again for all the help and suggestions. Armand On Tue, Apr 2, 2013 at 11:55 AM, Armand du Plessis wrote: > Jumped the gun a bit. the problem still exists like before. But it's > definitely on the right track, below is the output from top in the seconds > before the cluster locks up. For some reason still insisting on moving > tasks around despite bumping the sched_migration_cost cost up to 100ms. > > 77 root RT 0 000 S 32.3 0.0 13:55.20 [migration/24] > > > > 26512 postgres 20 0 8601m 7388 4992 R 32.3 0.0 0:02.17 postgres: > other_user (52944) INSERT > > >38 root RT 0 000 S 31.3 0.0 17:26.15 > [migration/11] > >65 root > RT 0 000 S 30.0 0.0 13:18.66 [migration/20] > > > >62 root RT 0 000 S 29.7 0.0 12:58.81 > [migration/19] > > >47 root RT 0 000 S 29.0 0.0 18:16.43 > [migration/14] > > >29 root RT 0 000 S 28.7 0.0 25:21.47 [migration/8] > > > >71 root RT 0 000 S 28.4 0.0 13:20.31 > [migration/22] > > >95 root RT 0 000 S 23.8 0.0 13:37.31 > [migration/30] > > > 26518 postgres 20 0 8601m 9684 5228 S 21.2 0.0 0:01.89 postgres: > other_user x(52954) INSERT > > > 6 root RT 0 000 S 20.5 0.0 39:17.72 [migration/0] > > > >41 root RT 0 000 S 19.6 0.0 18:21.36 > [migration/12] > > >68 root RT 0 000 S 19.6 0.0 13:04.62 > [migration/21] > > >74 root RT 0 000 S 18.9 0.0 13:39.41 > [migration/23] > > > 305 root 20 0 000 S 18.3 0.0 11:34.52 > [kworker/27:1] > > >44 root RT 0 000 S 17.0 0.0 18:30.71 > [migration/13] > > >89 root RT 0 000 S 16.0 0.0 12:13.42 > [migration/28] > > > 7 root RT 0 000 S 15.3 0.0 21:58.56 [migration/1] > > > >35 root RT 0 000 S 15.3 0.0 20:02.05 > [migration/10] > > >53 root RT 0 000 S 14.0 0.0 12:51.46 > [migration/16] > > > 11254 root 0 -20 21848 7532 2788 S 11.7 0.0 22:35.66 atop 1 > > > >14 root RT 0 000 S 10.8 0.0 19:36.56 [migration/3] > > > > 26463 postgres 20 0 8601m 7492 5100 R 10.8 0.0 0:00.33 postgres: > other_user x(32835) INSERT > > >32 root RT 0 000 S 10.1 0.0 20:46.18 [migration/9] > > > > 16793 root 20 0 000 S 6.5 0.0 1:12.72 > [kworker/25:0] > > >20 root RT 0 000 S 5.5 0.0 18:51.81 [migration/5] > > > >48 root 20 0 000 S 5.5 0.0 3:52.93 > [kworker/14:0] > > > On Tue, Apr 2, 2013 at 10:16 AM, Armand du Plessis wrote: > >> Touch wood but I think I found the problem thanks to these pointers. I >> checked the vm.zone_reclaim_mode and mine was set to 0. However just >> before the locking starts I can see many of my CPUs flashing red and jump >> to high percentage sys usage. When I look at top it's the migration kernel >> tasks that seem to trigger it. >> >> So it seems it was a bit trigger happy with task migrations, setting the >> kernel.sched_migration_cost >> to 500 (5ms) seemed to have resolved my woes. I'm yet to see locks >> climb and it's been running stable for a bit. This post was invaluable in >> explaining the cause -> >> http://www.postgresql.org/
Re: [PERFORM] Problems with pg_locks explosion
Jumped the gun a bit. the problem still exists like before. But it's definitely on the right track, below is the output from top in the seconds before the cluster locks up. For some reason still insisting on moving tasks around despite bumping the sched_migration_cost cost up to 100ms. 77 root RT 0 000 S 32.3 0.0 13:55.20 [migration/24] 26512 postgres 20 0 8601m 7388 4992 R 32.3 0.0 0:02.17 postgres: other_user (52944) INSERT 38 root RT 0 000 S 31.3 0.0 17:26.15 [migration/11] 65 root RT 0 0 00 S 30.0 0.0 13:18.66 [migration/20] 62 root RT 0 000 S 29.7 0.0 12:58.81 [migration/19] 47 root RT 0 000 S 29.0 0.0 18:16.43 [migration/14] 29 root RT 0 000 S 28.7 0.0 25:21.47 [migration/8] 71 root RT 0 000 S 28.4 0.0 13:20.31 [migration/22] 95 root RT 0 000 S 23.8 0.0 13:37.31 [migration/30] 26518 postgres 20 0 8601m 9684 5228 S 21.2 0.0 0:01.89 postgres: other_user x(52954) INSERT 6 root RT 0 000 S 20.5 0.0 39:17.72 [migration/0] 41 root RT 0 000 S 19.6 0.0 18:21.36 [migration/12] 68 root RT 0 000 S 19.6 0.0 13:04.62 [migration/21] 74 root RT 0 000 S 18.9 0.0 13:39.41 [migration/23] 305 root 20 0 000 S 18.3 0.0 11:34.52 [kworker/27:1] 44 root RT 0 000 S 17.0 0.0 18:30.71 [migration/13] 89 root RT 0 000 S 16.0 0.0 12:13.42 [migration/28] 7 root RT 0 000 S 15.3 0.0 21:58.56 [migration/1] 35 root RT 0 000 S 15.3 0.0 20:02.05 [migration/10] 53 root RT 0 000 S 14.0 0.0 12:51.46 [migration/16] 11254 root 0 -20 21848 7532 2788 S 11.7 0.0 22:35.66 atop 1 14 root RT 0 000 S 10.8 0.0 19:36.56 [migration/3] 26463 postgres 20 0 8601m 7492 5100 R 10.8 0.0 0:00.33 postgres: other_user x(32835) INSERT 32 root RT 0 000 S 10.1 0.0 20:46.18 [migration/9] 16793 root 20 0 000 S 6.5 0.0 1:12.72 [kworker/25:0] 20 root RT 0 000 S 5.5 0.0 18:51.81 [migration/5] 48 root 20 0 000 S 5.5 0.0 3:52.93 [kworker/14:0] On Tue, Apr 2, 2013 at 10:16 AM, Armand du Plessis wrote: > Touch wood but I think I found the problem thanks to these pointers. I > checked the vm.zone_reclaim_mode and mine was set to 0. However just > before the locking starts I can see many of my CPUs flashing red and jump > to high percentage sys usage. When I look at top it's the migration kernel > tasks that seem to trigger it. > > So it seems it was a bit trigger happy with task migrations, setting the > kernel.sched_migration_cost > to 500 (5ms) seemed to have resolved my woes. I'm yet to see locks > climb and it's been running stable for a bit. This post was invaluable in > explaining the cause -> > http://www.postgresql.org/message-id/50e4aab1.9040...@optionshouse.com > > # Postgres Kernel Tweaks > kernel.sched_migration_cost = 500 > # kernel.sched_autogroup_enabled = 0 > > The second recommended setting 'sched_autogroup_enabled' is not available > on the kernel I'm running but it doesn't seem to be a problem. > > Again, thanks again for the help. It was seriously appreciated. Long night > was long. > > If things change and the problem pops up again I'll update you guys. > > Cheers, > > Armand > > > On Tue, Apr 2, 2013 at 8:43 AM, Mark Kirkwood < > mark.kirkw...@catalyst.net.nz> wrote: > >> Also it is worth checking what your sysctl vm.zone_reclaim_mode is set to >> - if 1 then override to 0. As Jeff mentioned, this gotcha for larger cpu >> number machines has been discussed at length on this list - but still traps >> us now and again! >> >> Cheers >> >> Mark > >
Re: [PERFORM] Problems with pg_locks explosion
Touch wood but I think I found the problem thanks to these pointers. I checked the vm.zone_reclaim_mode and mine was set to 0. However just before the locking starts I can see many of my CPUs flashing red and jump to high percentage sys usage. When I look at top it's the migration kernel tasks that seem to trigger it. So it seems it was a bit trigger happy with task migrations, setting the kernel.sched_migration_cost to 500 (5ms) seemed to have resolved my woes. I'm yet to see locks climb and it's been running stable for a bit. This post was invaluable in explaining the cause -> http://www.postgresql.org/message-id/50e4aab1.9040...@optionshouse.com # Postgres Kernel Tweaks kernel.sched_migration_cost = 500 # kernel.sched_autogroup_enabled = 0 The second recommended setting 'sched_autogroup_enabled' is not available on the kernel I'm running but it doesn't seem to be a problem. Again, thanks again for the help. It was seriously appreciated. Long night was long. If things change and the problem pops up again I'll update you guys. Cheers, Armand On Tue, Apr 2, 2013 at 8:43 AM, Mark Kirkwood wrote: > Also it is worth checking what your sysctl vm.zone_reclaim_mode is set to > - if 1 then override to 0. As Jeff mentioned, this gotcha for larger cpu > number machines has been discussed at length on this list - but still traps > us now and again! > > Cheers > > Mark > > > On 02/04/13 19:33, Armand du Plessis wrote: > >> I had my reservations about my almost 0% IO usage on the raid0 array as >> well. I'm looking at the numbers in atop and it doesn't seem to reflect >> the aggregate of the volumes as one would expect. I'm just happy I am >> seeing numbers on the volumes, they're not too bad. >> >> One thing I was wondering, as a last possible IO resort. Provisioned EBS >> volumes requires that you maintain a wait queue of 1 for every 200 >> provisioned IOPS to get reliable IO. My wait queue hovers between 0-1 >> and with the 1000 IOPS it should be 5. Even thought about artificially >> pushing more IO to the volumes but I think Jeff's right, there's some >> internal kernel voodoo at play here. I have a feeling it'll be under >> control with pg_pool (if I can just get the friggen setup there right) >> and then I'll have more time to dig into it deeper. >> >> Apologies to the kittens for the interrupting your leave :) >> >> >
Re: [PERFORM] Problems with pg_locks explosion
Also it is worth checking what your sysctl vm.zone_reclaim_mode is set to - if 1 then override to 0. As Jeff mentioned, this gotcha for larger cpu number machines has been discussed at length on this list - but still traps us now and again! Cheers Mark On 02/04/13 19:33, Armand du Plessis wrote: I had my reservations about my almost 0% IO usage on the raid0 array as well. I'm looking at the numbers in atop and it doesn't seem to reflect the aggregate of the volumes as one would expect. I'm just happy I am seeing numbers on the volumes, they're not too bad. One thing I was wondering, as a last possible IO resort. Provisioned EBS volumes requires that you maintain a wait queue of 1 for every 200 provisioned IOPS to get reliable IO. My wait queue hovers between 0-1 and with the 1000 IOPS it should be 5. Even thought about artificially pushing more IO to the volumes but I think Jeff's right, there's some internal kernel voodoo at play here. I have a feeling it'll be under control with pg_pool (if I can just get the friggen setup there right) and then I'll have more time to dig into it deeper. Apologies to the kittens for the interrupting your leave :) -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Problems with pg_locks explosion
I had my reservations about my almost 0% IO usage on the raid0 array as well. I'm looking at the numbers in atop and it doesn't seem to reflect the aggregate of the volumes as one would expect. I'm just happy I am seeing numbers on the volumes, they're not too bad. One thing I was wondering, as a last possible IO resort. Provisioned EBS volumes requires that you maintain a wait queue of 1 for every 200 provisioned IOPS to get reliable IO. My wait queue hovers between 0-1 and with the 1000 IOPS it should be 5. Even thought about artificially pushing more IO to the volumes but I think Jeff's right, there's some internal kernel voodoo at play here. I have a feeling it'll be under control with pg_pool (if I can just get the friggen setup there right) and then I'll have more time to dig into it deeper. Apologies to the kittens for the interrupting your leave :) On Tue, Apr 2, 2013 at 8:25 AM, Mark Kirkwood wrote: > On 02/04/13 19:08, Jeff Janes wrote: > >> On Monday, April 1, 2013, Mark Kirkwood wrote: >> >> >> Your provisioned volumes are much better than the default AWS ones, >> but are still not hugely fast (i.e 1000 IOPS is about 8 MB/s worth >> of Postgres 8k buffers). So you may need to look at adding more >> volumes into the array, or adding some separate ones and putting >> pg_xlog directory on 'em. >> >> However before making changes I would recommend using iostat or sar >> to monitor how volumes are handling the load (I usually choose a 1 >> sec granularity and look for 100% util and high - server hundred ms >> - awaits). Also iotop could be enlightening. >> >> >> Hi Mark, >> >> Do you have experience using these tools with AWS? When using non-DAS >> in other contexts, I've noticed that these tools often give deranged >> results, because the kernel doesn't correctly know what time to >> attribute to "network" and what to attribute to "disk". But I haven't >> looked into it on AWS EBS, maybe they do a better job there. >> Thanks for any insight, >> >> > > > Hi Jeff, > > That is a very good point. I did notice a reasonable amount of network > traffic on the graphs posted previously, along with a suspiciously low > amount of IO for md127 (which I assume is the raid0 array)...and wondered > if iostat was not seeing IO fully, however it slipped my mind (I am on > leave with kittens - so claim that for the purrrfect excuse)! > > However I don't recall there being a problem with the io tools for > standard EBS volumes - but I haven't benchmarked AWS for a over a year, so > things could be different now - and I have no experience with these new > provisioned volumes. > > Armand - it might be instructive to do some benchmarking (with another > host and volume set) where you do something like: > > $ dd if=/dev/zero of=file bs=8k count=100 > > and see if iostat and friends actually show you doing IO as expected! > > > >
Re: [PERFORM] Problems with pg_locks explosion
On 02/04/13 19:08, Jeff Janes wrote: On Monday, April 1, 2013, Mark Kirkwood wrote: Your provisioned volumes are much better than the default AWS ones, but are still not hugely fast (i.e 1000 IOPS is about 8 MB/s worth of Postgres 8k buffers). So you may need to look at adding more volumes into the array, or adding some separate ones and putting pg_xlog directory on 'em. However before making changes I would recommend using iostat or sar to monitor how volumes are handling the load (I usually choose a 1 sec granularity and look for 100% util and high - server hundred ms - awaits). Also iotop could be enlightening. Hi Mark, Do you have experience using these tools with AWS? When using non-DAS in other contexts, I've noticed that these tools often give deranged results, because the kernel doesn't correctly know what time to attribute to "network" and what to attribute to "disk". But I haven't looked into it on AWS EBS, maybe they do a better job there. Thanks for any insight, Hi Jeff, That is a very good point. I did notice a reasonable amount of network traffic on the graphs posted previously, along with a suspiciously low amount of IO for md127 (which I assume is the raid0 array)...and wondered if iostat was not seeing IO fully, however it slipped my mind (I am on leave with kittens - so claim that for the purrrfect excuse)! However I don't recall there being a problem with the io tools for standard EBS volumes - but I haven't benchmarked AWS for a over a year, so things could be different now - and I have no experience with these new provisioned volumes. Armand - it might be instructive to do some benchmarking (with another host and volume set) where you do something like: $ dd if=/dev/zero of=file bs=8k count=100 and see if iostat and friends actually show you doing IO as expected! -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Problems with pg_locks explosion
Thanks Jeff, yup, I'm actually busy setting up pg_pool now. Preliminary results looks promising after switching some client nodes to connect through the pool. Here's the output of pg_stat_dabatase but also doesn't seem to be spending more time there either. I'll have a look through the archives for the posts you refer to. Certainly a simple 'upgrade' that's gone south badly here. On paper and with earlier tests with partial load this instance is much better suited for our workload, bizarre. Thanks for all the help. user=# select * from pg_stat_database; datid | datname | numbackends | xact_commit | xact_rollback | blks_read | blks_hit | tup_returned | tup_fetched | tup_inserted | tup_updated | tup_deleted | conflicts | temp_files | temp_bytes | deadlocks | blk_read_time | blk_write_time | stats_ reset ---+---+-+-+---+---+--+--+--+--+-+-+---++-+---+---++ 17671 | production| 232 | 524583730 |213187 | 623507632 | 403590060861 | 256853219556 | 185283046675 | 95086454 | 66720609 | 4449894 | 0 | 18 | 12076277760 | 0 | 4689747.806 | 4526.539 | 2013-03-29 16:1 8:09.334432+00 On Tue, Apr 2, 2013 at 8:08 AM, Jeff Janes wrote: > On Monday, April 1, 2013, Armand du Plessis wrote: > >> I've run an EXPLAIN ANALYZE on one of the queries that appeared in the >> pg_locks (although like you say that might be a red herring) both during >> normal response times (2) and also after the locks backlog materialized (1) >> >> The output below, I've just blanked out some columns. The IO timings do >> seem an order of magnitude slower but not excessive unless I'm reading it >> wrong. >> >> "Limit (cost=2364.19..2365.44 rows=500 width=177) (actual >> time=6501.103..6507.196 rows=500 loops=1)" >> " Output: >> " Buffers: shared hit=7163 read=137" >> " I/O Timings: read=107.771" >> > > ... > > >> >> "Limit (cost=2366.57..2367.82 rows=500 width=177) (actual time= >> 73.284..76.296 rows=500 loops=1)" >> " Output: various columns" >> " Buffers: shared hit=6738 read=562" >> " I/O Timings: read=19.212" >> > > You are correct that the different in IO timing for reads is not nearly > enough to explain the difference, but the ratio is still large enough to > perhaps be suggestive. It could be be that all the extra time is spent in > IO writes (not reported here). If you turn on track_io_timing on > system-wide you could check the write times in pg_stat_database. > > (Write time has an attribution problem. I need to make room for my data, > so I write out someone else's. Is the time spent attributed to the one > doing the writing, or the one who owns the data written?) > > But it is perhaps looking like it might not be IO at all, but rather some > kind of internal kernel problem, such as the "zone reclaim" and "huge > pages" and memory interleaving, which have been discussed elsewhere in this > list for high CPU high RAM machines. I would summarize it for you, but I > don't understand it, and don't have ready access to machines with 64 CPUs > and 128 GB of RAM in order to explore it for myself. > > But if that is the case, then using a connection pooler to restrict the > number of simultaneously active connections might actually be a big win > (despite what I said previously). > > Cheers, > > Jeff >
Re: [PERFORM] Problems with pg_locks explosion
On Monday, April 1, 2013, Armand du Plessis wrote: > I've run an EXPLAIN ANALYZE on one of the queries that appeared in the > pg_locks (although like you say that might be a red herring) both during > normal response times (2) and also after the locks backlog materialized (1) > > The output below, I've just blanked out some columns. The IO timings do > seem an order of magnitude slower but not excessive unless I'm reading it > wrong. > > "Limit (cost=2364.19..2365.44 rows=500 width=177) (actual > time=6501.103..6507.196 rows=500 loops=1)" > " Output: > " Buffers: shared hit=7163 read=137" > " I/O Timings: read=107.771" > ... > > "Limit (cost=2366.57..2367.82 rows=500 width=177) (actual > time=73.284..76.296 rows=500 loops=1)" > " Output: various columns" > " Buffers: shared hit=6738 read=562" > " I/O Timings: read=19.212" > You are correct that the different in IO timing for reads is not nearly enough to explain the difference, but the ratio is still large enough to perhaps be suggestive. It could be be that all the extra time is spent in IO writes (not reported here). If you turn on track_io_timing on system-wide you could check the write times in pg_stat_database. (Write time has an attribution problem. I need to make room for my data, so I write out someone else's. Is the time spent attributed to the one doing the writing, or the one who owns the data written?) But it is perhaps looking like it might not be IO at all, but rather some kind of internal kernel problem, such as the "zone reclaim" and "huge pages" and memory interleaving, which have been discussed elsewhere in this list for high CPU high RAM machines. I would summarize it for you, but I don't understand it, and don't have ready access to machines with 64 CPUs and 128 GB of RAM in order to explore it for myself. But if that is the case, then using a connection pooler to restrict the number of simultaneously active connections might actually be a big win (despite what I said previously). Cheers, Jeff >
Re: [PERFORM] Problems with pg_locks explosion
On Monday, April 1, 2013, Mark Kirkwood wrote: > > Your provisioned volumes are much better than the default AWS ones, but > are still not hugely fast (i.e 1000 IOPS is about 8 MB/s worth of Postgres > 8k buffers). So you may need to look at adding more volumes into the array, > or adding some separate ones and putting pg_xlog directory on 'em. > > However before making changes I would recommend using iostat or sar to > monitor how volumes are handling the load (I usually choose a 1 sec > granularity and look for 100% util and high - server hundred ms - awaits). > Also iotop could be enlightening. > Hi Mark, Do you have experience using these tools with AWS? When using non-DAS in other contexts, I've noticed that these tools often give deranged results, because the kernel doesn't correctly know what time to attribute to "network" and what to attribute to "disk". But I haven't looked into it on AWS EBS, maybe they do a better job there. Thanks for any insight, Jeff
Re: Fwd: [PERFORM] Problems with pg_locks explosion
Yeah, as I understand it you should have 6000 IOPS available for the md device (ideally). The iostats you display certainly look benign... but the key time to be sampling would be when you see the lock list explode - could look very different then. Re vm.dirty* - I would crank the values down by a factor of 5: vm.dirty_background_ratio = 1 (down from 5) vm.dirty_ratio = 2 (down from 10) Assuming of course that you actually are seeing an IO stall (which should be catchable via iostat or iotop)... and not some other issue. Otherwise leave 'em alone and keep looking :-) Cheers Mark On 02/04/13 13:31, Armand du Plessis wrote: I had a look at the iostat output (on a 5s interval) and pasted it below. The utilization and waits seems low. Included a sample below, #1 taken during normal operation and then when the locks happen it basically drops to 0 across the board. My (mis)understanding of the IOPS was that it would be 1000 IOPS per/volume and when in RAID0 should give me quite a bit higher throughput than in a single EBS volume setup. (My naive envelop calculation was #volumes * PIOPS = Effective IOPS :/) I'm looking into vm.dirty_background_ratio, vm.dirty_ratio sysctls. Is there any guidance or links available that would be useful as a starting point? Thanks again for the help, I really appreciate it. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Problems with pg_locks explosion
Hi Steven, Sounds very familiar. Painfully familiar :( But I really don't know. All I can see is that in this particular configuration the instance has 2 x Intel Xeon E5-2670, eight-core processors. I can't find any info on whether it's flex or round robin. AWS typically don't make the underlying hardware known. The exception is on the chip-types on the higher-end instance types which is where I got the info above from. Below is an excerpt from atop when the problem occur. The CPUs jump to high sys usage, not sure if that was similar to what you saw? How did you get it resolved in the end? ATOP - ip-10-155-231-112 2013/04/02 01:25:40 -- 2s elapsed 59;169H 0 70.15s | | user 8.19s | | | | | #proc 1015 | | #zombie0 | | clones 0 | | | | | #exit 2 | CPU | sys3182% | | user 30% | | irq 1% | | | | idle 0% | | wait 0% | | | | steal 0% | | guest 0% | cpu | sys 98% | | user 1% | | irq 1% | | | | idle 0% | | cpu000 w 0% | | | | steal 0% | | guest 0% | cpu | sys 96% | | user 4% | | irq 0% | | | | idle 0% | | cpu001 w 0% | | | | steal 0% | | guest 0% | cpu | sys 100% | | user 0% | | irq 0% | | | | idle 0% | | cpu002 w 0% | | | | steal 0% | | guest 0% | cpu | sys 99% | | user 1% | | irq 0% | | | | idle 0% | | cpu003 w 0% | | | | steal 0% | | guest 0% | cpu | sys 100% | | user 0% | | irq 0% | | | | idle 0% | | cpu004 w 0% | | | | steal 0% | | guest 0% | cpu | sys 100% | | user 0% | | irq 0% | | | | idle 0% | | cpu005 w 0% | | | | steal 0% | | guest 0% | cpu | sys 98% | | user 2% | | irq 0% | | | | idle 0% | | cpu006 w 0% | | | | steal 0% | | guest 0% | cpu | sys 99% | | user 1% | | irq 0% | | | | idle 0% | | cpu007 w 0% | | | | steal 0% | | guest 0% | cpu | sys 99% | | user 1% | | irq 0% | | | | idle 0% | | cpu008 w 0% | | | | steal 0% | | guest 0% | cpu | sys 100% | | user 0% | | irq 0% | | | | idle 0% | | cpu009 w 0% | | | | steal 0% | | guest 0% | cpu | sys 99% | | user 1% | | irq 0% | | | | idle 0% | | cpu010 w 0% | | | | steal 0% | | guest 0% | cpu | sys 100% | | user 0% | | irq 0% | | | | idle 0% | | cpu011 w 0% | | | | steal 0% | | guest 0% | cpu | sys 99% | | user 1% | | irq 0% | | | | idle 0% | | cpu012 w 0% | | | | steal 0% | | guest 0% | cpu | sys 97% | | user 3% | | irq 0% | | | | idle 0% | | cpu013 w 0% | | | | steal 0% |
Re: [PERFORM] Problems with pg_locks explosion
Armand, All of the symptoms you describe line up perfectly with a problem I had recently when upgrading DB hardware. Everything ran find until we hit some threshold somewhere at which point the locks would pile up in the thousands just as you describe, all while we were not I/O bound. I was moving from a DELL 810 that used a flex memory bridge to a DELL 820 that used round robin on their quad core intels. (Interestingly we also found out that DELL is planning on rolling back to the flex memory bridge later this year.) Any chance you could find out if your old processors might have been using flex while you're new processors might be using round robin? -s On Mon, Apr 1, 2013 at 5:59 PM, Armand du Plessis wrote: > I've run an EXPLAIN ANALYZE on one of the queries that appeared in the > pg_locks (although like you say that might be a red herring) both during > normal response times (2) and also after the locks backlog materialized (1) > > The output below, I've just blanked out some columns. The IO timings do > seem an order of magnitude slower but not excessive unless I'm reading it > wrong. > > "Limit (cost=2364.19..2365.44 rows=500 width=177) (actual > time=6501.103..6507.196 rows=500 loops=1)" > " Output: > " Buffers: shared hit=7163 read=137" > " I/O Timings: read=107.771" > " -> Sort (cost=2364.19..2365.56 rows=549 width=177) (actual > time=6501.095..6503.216 rows=500 loops=1)" > "Output: > "Sort Key: messages.created_at" > "Sort Method: quicksort Memory: 294kB" > "Buffers: shared hit=7163 read=137" > "I/O Timings: read=107.771" > "-> Nested Loop (cost=181.19..2339.21 rows=549 width=177) > (actual time=6344.410..6495.377 rows=783 loops=1)" > " Output: > " Buffers: shared hit=7160 read=137" > " I/O Timings: read=107.771" > " -> Nested Loop (cost=181.19..1568.99 rows=549 width=177) > (actual time=6344.389..6470.549 rows=783 loops=1)" > "Output: > "Buffers: shared hit=3931 read=137" > "I/O Timings: read=107.771" > "-> Bitmap Heap Scan on public.messages > (cost=181.19..798.78 rows=549 width=177) (actual time=6344.342..6436.117 > rows=783 loops=1)" > " Output: > " Recheck Cond: > " Buffers: shared hit=707 read=137" > " I/O Timings: read=107.771" > " -> BitmapOr (cost=181.19..181.19 rows=549 > width=0) (actual time=6344.226..6344.226 rows=0 loops=1)" > "Buffers: shared hit=120 read=20" > "I/O Timings: read=37.085" > "-> Bitmap Index Scan on > messages_sender_type_created_at_idx (cost=0.00..23.41 rows=309 width=0) > (actual time=6343.358..6343.358 rows=366 loops=1)" > " Index Cond: > " Buffers: shared hit=26 read=15" > " I/O Timings: read=36.977" > "-> Bitmap Index Scan on > messages_type_sender_recipient_created_at > " Buffers: shared hit=94 read=5" > " I/O Timings: read=0.108" > "-> Index Only Scan using profiles_pkey on > public.profiles (cost=0.00..1.39 rows=1 width=4) (actual time=0.018..0.024 > rows=1 loops=783)" > " Output: profiles.id" > " Index Cond: (profiles.id = messages.sender)" > " Heap Fetches: 661" > " Buffers: shared hit=3224" > " -> Index Only Scan using profiles_pkey on public.profiles > recipient_profiles_messages (cost=0.00..1.39 rows=1 width=4) (actual > time=0.014..0.018 rows=1 loops=783)" > "Output: recipient_profiles_messages.id" > "Index Cond: (recipient_profiles_messages.id = > messages.recipient)" > "Heap Fetches: 667" > "Buffers: shared hit=3229" > "Total runtime: 6509.328 ms" > > > > "Limit (cost=2366.57..2367.82 rows=500 width=177) (actual time= > 73.284..76.296 rows=500 loops=1)" > " Output: various columns" > " Buffers: shared hit=6738 read=562" > " I/O Timings: read=19.212" > " -> Sort (cost=2366.57..2367.94 rows=549 width=177) (actual time= > 73.276..74.300 rows=500 loops=1)" > "Output: various columns" > "Sort Key: messages.created_at" > "Sort Method: quicksort Memory: 294kB" > "Buffers: shared hit=6738 read=562" > "I/O Timings: read=19.212" > "-> Nested Loop (cost=181.19..2341.59 rows=549 width=177) > (actual time=3.556..69.866 rows=783 loops=1)" > " Output: various columns > " Buffers: shared hit=6735 read=562" > " I/O Timings: re
Re: [PERFORM] Problems with pg_locks explosion
I've run an EXPLAIN ANALYZE on one of the queries that appeared in the pg_locks (although like you say that might be a red herring) both during normal response times (2) and also after the locks backlog materialized (1) The output below, I've just blanked out some columns. The IO timings do seem an order of magnitude slower but not excessive unless I'm reading it wrong. "Limit (cost=2364.19..2365.44 rows=500 width=177) (actual time=6501.103..6507.196 rows=500 loops=1)" " Output: " Buffers: shared hit=7163 read=137" " I/O Timings: read=107.771" " -> Sort (cost=2364.19..2365.56 rows=549 width=177) (actual time=6501.095..6503.216 rows=500 loops=1)" "Output: "Sort Key: messages.created_at" "Sort Method: quicksort Memory: 294kB" "Buffers: shared hit=7163 read=137" "I/O Timings: read=107.771" "-> Nested Loop (cost=181.19..2339.21 rows=549 width=177) (actual time=6344.410..6495.377 rows=783 loops=1)" " Output: " Buffers: shared hit=7160 read=137" " I/O Timings: read=107.771" " -> Nested Loop (cost=181.19..1568.99 rows=549 width=177) (actual time=6344.389..6470.549 rows=783 loops=1)" "Output: "Buffers: shared hit=3931 read=137" "I/O Timings: read=107.771" "-> Bitmap Heap Scan on public.messages (cost=181.19..798.78 rows=549 width=177) (actual time=6344.342..6436.117 rows=783 loops=1)" " Output: " Recheck Cond: " Buffers: shared hit=707 read=137" " I/O Timings: read=107.771" " -> BitmapOr (cost=181.19..181.19 rows=549 width=0) (actual time=6344.226..6344.226 rows=0 loops=1)" "Buffers: shared hit=120 read=20" "I/O Timings: read=37.085" "-> Bitmap Index Scan on messages_sender_type_created_at_idx (cost=0.00..23.41 rows=309 width=0) (actual time=6343.358..6343.358 rows=366 loops=1)" " Index Cond: " Buffers: shared hit=26 read=15" " I/O Timings: read=36.977" "-> Bitmap Index Scan on messages_type_sender_recipient_created_at " Buffers: shared hit=94 read=5" " I/O Timings: read=0.108" "-> Index Only Scan using profiles_pkey on public.profiles (cost=0.00..1.39 rows=1 width=4) (actual time=0.018..0.024 rows=1 loops=783)" " Output: profiles.id" " Index Cond: (profiles.id = messages.sender)" " Heap Fetches: 661" " Buffers: shared hit=3224" " -> Index Only Scan using profiles_pkey on public.profiles recipient_profiles_messages (cost=0.00..1.39 rows=1 width=4) (actual time=0.014..0.018 rows=1 loops=783)" "Output: recipient_profiles_messages.id" "Index Cond: (recipient_profiles_messages.id = messages.recipient)" "Heap Fetches: 667" "Buffers: shared hit=3229" "Total runtime: 6509.328 ms" "Limit (cost=2366.57..2367.82 rows=500 width=177) (actual time=73.284..76.296 rows=500 loops=1)" " Output: various columns" " Buffers: shared hit=6738 read=562" " I/O Timings: read=19.212" " -> Sort (cost=2366.57..2367.94 rows=549 width=177) (actual time=73.276..74.300 rows=500 loops=1)" "Output: various columns" "Sort Key: messages.created_at" "Sort Method: quicksort Memory: 294kB" "Buffers: shared hit=6738 read=562" "I/O Timings: read=19.212" "-> Nested Loop (cost=181.19..2341.59 rows=549 width=177) (actual time=3.556..69.866 rows=783 loops=1)" " Output: various columns " Buffers: shared hit=6735 read=562" " I/O Timings: read=19.212" " -> Nested Loop (cost=181.19..1570.19 rows=549 width=177) (actual time=3.497..53.820 rows=783 loops=1)" "Output: various columns "Buffers: shared hit=3506 read=562" "I/O Timings: read=19.212" "-> Bitmap Heap Scan on public.messages (cost=181.19..798.78 rows=549 width=177) (actual time=3.408..32.906 rows=783 loops=1)" " Output: various columns " Recheck Cond: () " Buffers: shared hit=282 read=562" " I/O Timings: read=19.212" " -> BitmapOr (cost=181.19..181.19 rows=549 width=0) (actual time=3.279..3.279 rows=0 loops=1)" "Buffers: shared hit=114 read=26" "I/O Timings: read=1.755" "
Re: [PERFORM] Problems with pg_locks explosion
Hi Jeff, Sorry I should've mentioned the new instance is Postgres 9.2.3. The old instance IO maxed out the disk/io available on a single EBS volume on AWS. It had 2000 PIOPS but was constantly bottlenecked. I assumed that striping 6 1000 IOPS volumes in RAID-0 would give me some breathing space on that front, and looking at the iostat (just included in previous email) it seems to be doing OK. I actually had pg_pool running as a test but to avoid having too many moving parts in the change removed it from the equation. Need to look into the proper configuration so it doesn't saturate my cluster worse than I'm doing myself. I've commented inline. Regards, Armand PS. This is probably the most helpful mailing list I've ever come across. Starting to feel a little more that it can be solved. On Tue, Apr 2, 2013 at 2:21 AM, Jeff Janes wrote: > On Mon, Apr 1, 2013 at 3:35 PM, Armand du Plessis wrote: > >> [Apologies, I first sent this to the incorrect list, postgres-admin, in >> the event you receive it twice] >> >> Hi there, >> >> I'm hoping someone on the list can shed some light on an issue I'm having >> with our Postgresql cluster. I'm literally tearing out my hair and don't >> have a deep enough understanding of Postgres to find the problem. >> >> What's happening is I had severe disk/io issues on our original Postgres >> cluster (9.0.8) >> > and switched to a new instance with a RAID-0 volume array. >> > > What was the old instance IO? Did you do IO benchmarking on both? > > >> The machine's CPU usage would hover around 30% and our database would >> run lightning fast with pg_locks hovering between 100-200. >> >> Within a few seconds something would trigger a massive increase in >> pg_locks so that it suddenly shoots up to 4000-8000. At this point >> everything dies. Queries that usually take a few milliseconds takes minutes >> and everything is unresponsive until I restart postgres. >> > > I think that pg_locks is pretty much a red herring. All it means is that > you have a lot more active connections than you used to. All active > connections are going to hold various locks, while most idle connections > (other than 'idle in transaction') connections will not hold any. > > Although I doubt it will solve this particular problem, you should > probably use a connection pooler. > > > >> shared_buffers = 32GB >> > > That seems very high. There are reports that using >8 GB leads to > precisely the type of problem you are seeing (checkpoint associated > freezes). Although I've never seen those reports when fsync=off. > > I thought you might be suffering from the problem solved in release 9.1 by > item "Merge duplicate fsync requests (Robert Haas, Greg Smith)", but then I > realized that with fsync=off it could not be that. > > > >> >> max_connections = 800 >> > > That also is very high. > > >> The problems seem to overlap with checkpoints. >> >> 2013-04-01 21:31:35.592 UTC,,,26877,,5159fa5f.68fd,1,,2013-04-01 21:21:35 >> UTC,,0,LOG,0,"checkpoint starting: time","" >> 2013-04-01 21:40:35.033 UTC,,,26877,,5159fa5f.68fd,2,,2013-04-01 21:21:35 >> UTC,,0,LOG,0,"checkpoint complete: wrote 100635 buffers (2.4%); 0 >> transaction log file(s) added, 0 removed, 1 recycled; write=539.439 s, >> sync=0.000 s, total=539.441 s; sync files=0, longest=0.000 s, average=0.000 >> s","" >> 2013-04-01 21:41:35.093 UTC,,,26877,,5159fa5f.68fd,3,,2013-04-01 21:21:35 >> UTC,,0,LOG,0,"checkpoint starting: time","" >> > > > I think you changed checkpoint_timout from default (5 min) to 10 minutes, > without telling us. Anyway, this is where it would be nice to know how > much of the 539.439 s in the write phase was spent blocking on writes, and > how much was spent napping. But that info is not collected by pgsql. > I did actually change it to 25 minutes. Apologies it was probably lost in the text of a previous email. Here's the changed settings: # - Background Writer - bgwriter_delay = 200ms # 10-1ms between rounds bgwriter_lru_maxpages = 400 # 0-1000 max buffers written/round bgwriter_lru_multiplier = 2.0 # 0-10.0 multipler on buffers scanned/round checkpoint_segments = 128 checkpoint_timeout = 25min It seems to be lasting longer with these settings. > > Your top output looked for it was a time at which there were no problems, > and it didn't include the top processes, so it wasn't very informative. > > If you could upgrade to 9.2 and capture some data with track_io_timing, > that could be useful. > I'm looking into track_io_timing. > > Cheers, > > Jeff >
Fwd: [PERFORM] Problems with pg_locks explosion
Thanks Mark, I had a look at the iostat output (on a 5s interval) and pasted it below. The utilization and waits seems low. Included a sample below, #1 taken during normal operation and then when the locks happen it basically drops to 0 across the board. My (mis)understanding of the IOPS was that it would be 1000 IOPS per/volume and when in RAID0 should give me quite a bit higher throughput than in a single EBS volume setup. (My naive envelop calculation was #volumes * PIOPS = Effective IOPS :/) Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util xvda 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdk 0.00 0.00 141.600.00 5084.80 0.0035.91 0.433.06 0.51 7.28 xvdj 0.00 0.00 140.400.40 4614.4024.0032.94 0.493.45 0.52 7.28 xvdi 0.00 0.00 123.002.00 4019.20 163.2033.46 0.332.63 0.68 8.48 xvdh 0.00 0.00 139.800.80 4787.2067.2034.53 0.523.73 0.55 7.68 xvdg 0.00 0.00 143.800.20 4804.8016.0033.48 0.866.03 0.72 10.40 xvdf 0.00 0.00 146.400.00 4758.40 0.0032.50 0.553.76 0.55 8.00 md127 0.00 0.00 831.203.40 27867.20 270.4033.71 0.000.00 0.00 0.00 avg-cpu: %user %nice %system %iowait %steal %idle 0.000.00 100.000.000.000.00 Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util xvda 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdk 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdj 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdi 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdh 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdg 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 xvdf 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 md127 0.00 0.000.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 It only spikes to 100% util when the server restarts. What bugs me though is Cloud Metrics show 100% Throughput on all the volumes despite the output above. I'm looking into vm.dirty_background_ratio, vm.dirty_ratio sysctls. Is there any guidance or links available that would be useful as a starting point? Thanks again for the help, I really appreciate it. Regards, Armand On Tue, Apr 2, 2013 at 2:11 AM, Mark Kirkwood wrote: > In addition to tuning the various Postgres config knobs you may need to > look at how your AWS server is set up. If your load is causing an IO stall > then *symptoms* of this will be lots of locks... > > You have quite a lot of memory (60G), so look at tuning the > vm.dirty_background_ratio, vm.dirty_ratio sysctls to avoid trying to > *suddenly* write out many gigs of dirty buffers. > > Your provisioned volumes are much better than the default AWS ones, but > are still not hugely fast (i.e 1000 IOPS is about 8 MB/s worth of Postgres > 8k buffers). So you may need to look at adding more volumes into the array, > or adding some separate ones and putting pg_xlog directory on 'em. > > However before making changes I would recommend using iostat or sar to > monitor how volumes are handling the load (I usually choose a 1 sec > granularity and look for 100% util and high - server hundred ms - awaits). > Also iotop could be enlightening. > > Regards > > Mark
Re: [PERFORM] Problems with pg_locks explosion
On Mon, Apr 1, 2013 at 3:35 PM, Armand du Plessis wrote: > [Apologies, I first sent this to the incorrect list, postgres-admin, in > the event you receive it twice] > > Hi there, > > I'm hoping someone on the list can shed some light on an issue I'm having > with our Postgresql cluster. I'm literally tearing out my hair and don't > have a deep enough understanding of Postgres to find the problem. > > What's happening is I had severe disk/io issues on our original Postgres > cluster (9.0.8) > and switched to a new instance with a RAID-0 volume array. > What was the old instance IO? Did you do IO benchmarking on both? > The machine's CPU usage would hover around 30% and our database would run > lightning fast with pg_locks hovering between 100-200. > > Within a few seconds something would trigger a massive increase in > pg_locks so that it suddenly shoots up to 4000-8000. At this point > everything dies. Queries that usually take a few milliseconds takes minutes > and everything is unresponsive until I restart postgres. > I think that pg_locks is pretty much a red herring. All it means is that you have a lot more active connections than you used to. All active connections are going to hold various locks, while most idle connections (other than 'idle in transaction') connections will not hold any. Although I doubt it will solve this particular problem, you should probably use a connection pooler. > shared_buffers = 32GB > That seems very high. There are reports that using >8 GB leads to precisely the type of problem you are seeing (checkpoint associated freezes). Although I've never seen those reports when fsync=off. I thought you might be suffering from the problem solved in release 9.1 by item "Merge duplicate fsync requests (Robert Haas, Greg Smith)", but then I realized that with fsync=off it could not be that. > > max_connections = 800 > That also is very high. > The problems seem to overlap with checkpoints. > > 2013-04-01 21:31:35.592 UTC,,,26877,,5159fa5f.68fd,1,,2013-04-01 21:21:35 > UTC,,0,LOG,0,"checkpoint starting: time","" > 2013-04-01 21:40:35.033 UTC,,,26877,,5159fa5f.68fd,2,,2013-04-01 21:21:35 > UTC,,0,LOG,0,"checkpoint complete: wrote 100635 buffers (2.4%); 0 > transaction log file(s) added, 0 removed, 1 recycled; write=539.439 s, > sync=0.000 s, total=539.441 s; sync files=0, longest=0.000 s, average=0.000 > s","" > 2013-04-01 21:41:35.093 UTC,,,26877,,5159fa5f.68fd,3,,2013-04-01 21:21:35 > UTC,,0,LOG,0,"checkpoint starting: time","" > I think you changed checkpoint_timout from default (5 min) to 10 minutes, without telling us. Anyway, this is where it would be nice to know how much of the 539.439 s in the write phase was spent blocking on writes, and how much was spent napping. But that info is not collected by pgsql. Your top output looked for it was a time at which there were no problems, and it didn't include the top processes, so it wasn't very informative. If you could upgrade to 9.2 and capture some data with track_io_timing, that could be useful. Cheers, Jeff
Re: [PERFORM] Problems with pg_locks explosion
In addition to tuning the various Postgres config knobs you may need to look at how your AWS server is set up. If your load is causing an IO stall then *symptoms* of this will be lots of locks... You have quite a lot of memory (60G), so look at tuning the vm.dirty_background_ratio, vm.dirty_ratio sysctls to avoid trying to *suddenly* write out many gigs of dirty buffers. Your provisioned volumes are much better than the default AWS ones, but are still not hugely fast (i.e 1000 IOPS is about 8 MB/s worth of Postgres 8k buffers). So you may need to look at adding more volumes into the array, or adding some separate ones and putting pg_xlog directory on 'em. However before making changes I would recommend using iostat or sar to monitor how volumes are handling the load (I usually choose a 1 sec granularity and look for 100% util and high - server hundred ms - awaits). Also iotop could be enlightening. Regards Mark On 02/04/13 11:35, Armand du Plessis wrote: It's on Amazon EC2 - * cc2.8xlarge instance type * 6 volumes in RAID-0 configuration. (1000 PIOPS) 60.5 GiB of memory 88 EC2 Compute Units (2 x Intel Xeon E5-2670, eight-core) 3370 GB of instance storage 64-bit platform I/O Performance: Very High (10 Gigabit Ethernet) EBS-Optimized Available: No** API name: cc2.8xlarge -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Problems with pg_locks explosion
Try these SQL statements , they will give you more information about whats
happening in your server lock-wise
SELECT
locktype, virtualtransaction,transactionid,nspname,relname,mode,granted,
cast(date_trunc('second',query_start) AS timestamp) AS query_start,
substr(current_query,1,25) AS query
FROM pg_locks
LEFT OUTER JOIN pg_class ON (pg_locks.relation = pg_class.oid)
LEFT OUTER JOIN pg_namespace ON (pg_namespace.oid = pg_class.
relnamespace), pg_stat_activity
WHERE
NOT pg_locks.pid=pg_backend_pid() AND pg_locks.pid=pg_stat_activity.procpid;
SELECT
locked.pid AS locked_pid, locker.pid AS locker_pid, locked_act.usename AS
locked_user, locker_act.usename AS locker_user,
locked.virtualtransaction, locked.transactionid, locked.locktype
FROM
pg_locks locked, pg_locks locker, pg_stat_activity locked_act,
pg_stat_activity locker_act
WHERE
locker.granted=true AND locked.granted=false AND
locked.pid=locked_act.procpid AND
locker.pid=locker_act.procpid AND
(locked.virtualtransaction=locker.virtualtransaction OR
locked.transactionid=locker.transactionid);
SELECT
locked.pid AS locked_pid, locker.pid AS locker_pid, locked_act.usename AS
locked_user, locker_act.usename AS locker_user,
locked.virtualtransaction, locked.transactionid, relname
FROM
pg_locks locked
LEFT OUTER JOIN pg_class ON (locked.relation = pg_class.oid), pg_locks
locker,pg_stat_activity locked_act, pg_stat_activity locker_act
WHERE
locker.granted=true AND locked.granted=false AND
locked.pid=locked_act.procpid AND locker.pid=locker_act.procpid AND
locked.relation=locker.relation;
Vasilis Ventirozos
Re: [PERFORM] Problems with pg_locks explosion
2 4184 4431168000 7617 133 20487 12364 9 > 1 90 0 0 > 6 0 0 368904 4184 4424815200 5162 6 22910 15221 14 > 7 80 0 0 > 2 0 0 383108 4184 4427678000 5846 1120 21109 12563 11 > 1 88 0 0 > 7 0 0 338348 4184 4427447200 9270 5 21243 12698 10 > 1 88 0 0 > 24 0 0 339676 4184 4421303600 663918 22976 12700 13 > 12 74 0 0 > 12 0 0 371848 4184 4414650000 657 133 18968 7445 5 53 > 43 0 0 > 37 0 0 374516 4184 440762120016 2 9156 4472 1 48 > 52 0 0 > 16 0 0 398412 4184 4397106000 127 0 9967 6018 0 48 > 52 0 0 > 4 0 0 417312 4184 4408439200 17434 1072 23661 14268 16 > 6 78 1 0 > 4 0 0 407672 4184 4413989600 5785 0 19779 11869 11 > 1 88 0 0 > 9 0 0 349544 4184 4405159600 6899 8 20376 12774 10 > 3 88 0 0 > 5 0 0 424628 4184 4405962800 9105 175 24546 15354 13 > 20 66 1 0 > 2 0 0 377164 4184 4407056400 9363 3 21191 12608 11 > 2 87 0 0 > 5 0 0 353360 4184 4404080400 6661 0 20931 12815 12 > 2 85 0 0 > 4 0 0 355144 4180 4403462000 7061 8 21264 12379 11 > 3 86 0 0 > procs ---memory-- ---swap-- -io --system-- > -cpu- > r b swpd free buff cache si sobibo in cs us sy id > wa st > 21 0 0 358396 4180 4395842000 7595 1749 23258 12299 10 > 27 63 0 0 > 6 1 0 437480 4160 4392215200 1756514 17059 14928 6 > 18 74 2 0 > 6 0 0 380304 4160 4399393200 10120 168 21519 12798 11 > 2 87 0 0 > 8 0 0 337740 4160 4400743200 6033 520 20872 12461 11 > 1 88 0 0 > 13 0 0 349712 4132 4392778400 6777 6 20919 12568 11 > 2 86 0 0 > 6 1 0 351180 4112 4389975600 8640 0 22543 12519 11 > 10 78 0 0 > 6 0 0 356392 4112 4392153200 620648 20383 12050 12 > 1 86 0 0 > 6 0 0 32 4108 4386344800 6106 3 21244 11817 9 > 9 82 0 0 > 3 0 0 364992 7312 4385682400 11283 199 21296 12638 13 > 2 85 0 0 > 4 1 0 371968 7120 4381855200 6715 1534 22322 13305 11 > 7 81 0 0 > debug2: channel 0: window 999365 sent adjust 49211 > 12 0 0 338540 7120 4382225600 9142 3 21520 12194 13 > 5 82 0 0 > 8 0 0 386016 7112 4371713600 2123 3 20465 11466 8 > 20 72 0 0 > 8 0 0 352388 7112 4371587200 1036651 25758 13879 16 > 19 65 0 0 > 20 0 0 351472 7112 4370106000 1309110 23766 12832 11 > 11 77 1 0 > 2 0 0 386820 7112 4358752000 482 210 17187 6773 3 69 > 28 0 0 > 64 0 0 401956 7112 4347372800 0 5 10796 9487 0 55 > 44 0 0 > > > On Tue, Apr 2, 2013 at 12:56 AM, Vasilis Ventirozos < > v.ventiro...@gmail.com> wrote: > >> Hello, i think that your system during the checkpoint pauses all clients >> in order to flush all data from controller's cache to the disks if i were >> you i'd try to tune my checkpoint parameters better, if that doesn't work, >> show us some vmstat output please >> >> Vasilis Ventirozos >> -- Forwarded message -- >> From: "Armand du Plessis" >> Date: Apr 2, 2013 1:37 AM >> Subject: [PERFORM] Problems with pg_locks explosion >> To: "pgsql-performance" >> Cc: >> >> [Apologies, I first sent this to the incorrect list, postgres-admin, in >> the event you receive it twice] >> >> Hi there, >> >> I'm hoping someone on the list can shed some light on an issue I'm having >> with our Postgresql cluster. I'm literally tearing out my hair and don't >> have a deep enough understanding of Postgres to find the problem. >> >> What's happening is I had severe disk/io issues on our original Postgres >> cluster (9.0.8) and switched to a new instance with a RAID-0 volume array. >> The machine's CPU usage would hover around 30% and our database would run >> lightning fast with pg_locks hovering between 100-200. >> >> Within a few seconds something would trigger a massive increase in >> pg_locks so that it suddenly shoots up to 4000-8000. At this point >> everything dies. Queries that usually take a few milliseconds takes minutes >> and everything is unresponsive until I restart postgres. >> >> The instance still idles at this point. The only
Re: [PERFORM] Problems with pg_locks explosion
0 0 355144 4180 4403462000 7061 8 21264 12379 11 3 86 0 0 procs ---memory-- ---swap-- -io --system-- -cpu- r b swpd free buff cache si sobibo in cs us sy id wa st 21 0 0 358396 4180 4395842000 7595 1749 23258 12299 10 27 63 0 0 6 1 0 437480 4160 4392215200 1756514 17059 14928 6 18 74 2 0 6 0 0 380304 4160 4399393200 10120 168 21519 12798 11 2 87 0 0 8 0 0 337740 4160 4400743200 6033 520 20872 12461 11 1 88 0 0 13 0 0 349712 4132 4392778400 6777 6 20919 12568 11 2 86 0 0 6 1 0 351180 4112 4389975600 8640 0 22543 12519 11 10 78 0 0 6 0 0 356392 4112 4392153200 620648 20383 12050 12 1 86 0 0 6 0 0 32 4108 4386344800 6106 3 21244 11817 9 9 82 0 0 3 0 0 364992 7312 4385682400 11283 199 21296 12638 13 2 85 0 0 4 1 0 371968 7120 4381855200 6715 1534 22322 13305 11 7 81 0 0 debug2: channel 0: window 999365 sent adjust 49211 12 0 0 338540 7120 4382225600 9142 3 21520 12194 13 5 82 0 0 8 0 0 386016 7112 4371713600 2123 3 20465 11466 8 20 72 0 0 8 0 0 352388 7112 4371587200 1036651 25758 13879 16 19 65 0 0 20 0 0 351472 7112 4370106000 1309110 23766 12832 11 11 77 1 0 2 0 0 386820 7112 4358752000 482 210 17187 6773 3 69 28 0 0 64 0 0 401956 7112 4347372800 0 5 10796 9487 0 55 44 0 0 On Tue, Apr 2, 2013 at 12:56 AM, Vasilis Ventirozos wrote: > Hello, i think that your system during the checkpoint pauses all clients > in order to flush all data from controller's cache to the disks if i were > you i'd try to tune my checkpoint parameters better, if that doesn't work, > show us some vmstat output please > > Vasilis Ventirozos > -- Forwarded message -- > From: "Armand du Plessis" > Date: Apr 2, 2013 1:37 AM > Subject: [PERFORM] Problems with pg_locks explosion > To: "pgsql-performance" > Cc: > > [Apologies, I first sent this to the incorrect list, postgres-admin, in > the event you receive it twice] > > Hi there, > > I'm hoping someone on the list can shed some light on an issue I'm having > with our Postgresql cluster. I'm literally tearing out my hair and don't > have a deep enough understanding of Postgres to find the problem. > > What's happening is I had severe disk/io issues on our original Postgres > cluster (9.0.8) and switched to a new instance with a RAID-0 volume array. > The machine's CPU usage would hover around 30% and our database would run > lightning fast with pg_locks hovering between 100-200. > > Within a few seconds something would trigger a massive increase in > pg_locks so that it suddenly shoots up to 4000-8000. At this point > everything dies. Queries that usually take a few milliseconds takes minutes > and everything is unresponsive until I restart postgres. > > The instance still idles at this point. The only clue I could find was > that it usually starts a few minutes after the checkpoint entries appear in > my logs. > > Any suggestions would really be appreciated. It's killing our business at > the moment. I can supply more info if required but pasted what I thought > would be useful below. Not sure what else to change in the settings. > > Kind regards, > > Armand > > > > It's on Amazon EC2 - > * cc2.8xlarge instance type > * 6 volumes in RAID-0 configuration. (1000 PIOPS) > > 60.5 GiB of memory > 88 EC2 Compute Units (2 x Intel Xeon E5-2670, eight-core) > 3370 GB of instance storage > 64-bit platform > I/O Performance: Very High (10 Gigabit Ethernet) > EBS-Optimized Available: No** > API name: cc2.8xlarge > > > postgresql.conf > fsync = off > full_page_writes = off > default_statistics_target = 100 > maintenance_work_mem = 1GB > checkpoint_completion_target = 0.9 > effective_cache_size = 48GB > work_mem = 64MB > wal_buffers = -1 > checkpoint_segments = 128 > shared_buffers = 32GB > max_connections = 800 > effective_io_concurrency = 3 # Down from 6 > > # - Background Writer - > > #bgwriter_delay = 200ms # 10-1ms between rounds > #bgwriter_lru_maxpages = 100# 0-1000 max buffers written/round > #bgwriter_lru_multiplier = 2.0 # 0-10.0 multipler on buffers > scanned/round > > > $ free > total used free sharedbuffers cached > Mem: 61368192 60988180 380012 0784 44167172 > -/+ buffers/cache: 1
Fwd: [PERFORM] Problems with pg_locks explosion
Hello, i think that your system during the checkpoint pauses all clients in order to flush all data from controller's cache to the disks if i were you i'd try to tune my checkpoint parameters better, if that doesn't work, show us some vmstat output please Vasilis Ventirozos -- Forwarded message -- From: "Armand du Plessis" Date: Apr 2, 2013 1:37 AM Subject: [PERFORM] Problems with pg_locks explosion To: "pgsql-performance" Cc: [Apologies, I first sent this to the incorrect list, postgres-admin, in the event you receive it twice] Hi there, I'm hoping someone on the list can shed some light on an issue I'm having with our Postgresql cluster. I'm literally tearing out my hair and don't have a deep enough understanding of Postgres to find the problem. What's happening is I had severe disk/io issues on our original Postgres cluster (9.0.8) and switched to a new instance with a RAID-0 volume array. The machine's CPU usage would hover around 30% and our database would run lightning fast with pg_locks hovering between 100-200. Within a few seconds something would trigger a massive increase in pg_locks so that it suddenly shoots up to 4000-8000. At this point everything dies. Queries that usually take a few milliseconds takes minutes and everything is unresponsive until I restart postgres. The instance still idles at this point. The only clue I could find was that it usually starts a few minutes after the checkpoint entries appear in my logs. Any suggestions would really be appreciated. It's killing our business at the moment. I can supply more info if required but pasted what I thought would be useful below. Not sure what else to change in the settings. Kind regards, Armand It's on Amazon EC2 - * cc2.8xlarge instance type * 6 volumes in RAID-0 configuration. (1000 PIOPS) 60.5 GiB of memory 88 EC2 Compute Units (2 x Intel Xeon E5-2670, eight-core) 3370 GB of instance storage 64-bit platform I/O Performance: Very High (10 Gigabit Ethernet) EBS-Optimized Available: No** API name: cc2.8xlarge postgresql.conf fsync = off full_page_writes = off default_statistics_target = 100 maintenance_work_mem = 1GB checkpoint_completion_target = 0.9 effective_cache_size = 48GB work_mem = 64MB wal_buffers = -1 checkpoint_segments = 128 shared_buffers = 32GB max_connections = 800 effective_io_concurrency = 3 # Down from 6 # - Background Writer - #bgwriter_delay = 200ms # 10-1ms between rounds #bgwriter_lru_maxpages = 100# 0-1000 max buffers written/round #bgwriter_lru_multiplier = 2.0 # 0-10.0 multipler on buffers scanned/round $ free total used free sharedbuffers cached Mem: 61368192 60988180 380012 0784 44167172 -/+ buffers/cache: 16820224 44547968 Swap:0 0 0 $ top -c top - 21:55:51 up 12 days, 12:41, 4 users, load average: 6.03, 16.10, 24.15 top - 21:55:54 up 12 days, 12:41, 4 users, load average: 6.03, 15.94, 24.06 Tasks: 837 total, 6 running, 831 sleeping, 0 stopped, 0 zombie Cpu(s): 15.7%us, 1.7%sy, 0.0%ni, 81.6%id, 0.3%wa, 0.0%hi, 0.6%si, 0.0%st Mem: 61368192k total, 54820988k used, 6547204k free, 9032k buffer [ec2-user@ip-10-155-231-112 ~]$ sudo iostat Linux 3.2.39-6.88.amzn1.x86_64 () 04/01/2013 _x86_64_ (32 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 21.000.001.100.260.00 77.63 Device:tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn xvda 0.21 5.00 2.2254118302401368 xvdk 98.32 1774.67 969.86 1919359965 1048932113 xvdj 98.28 1773.68 969.14 1918288697 1048156776 xvdi 98.29 1773.69 969.61 1918300250 1048662470 xvdh 98.24 1773.92 967.54 1918544618 1046419936 xvdg 98.27 1774.15 968.85 1918790636 1047842846 xvdf 98.32 1775.56 968.69 1920316435 1047668172 md127 733.85 10645.68 5813.70 11513598393 6287682313 What bugs me on this is the throughput percentage on the volumes in Cloudwatch is 100% on all volumes. The problems seem to overlap with checkpoints. 2013-04-01 21:31:35.592 UTC,,,26877,,5159fa5f.68fd,1,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint starting: time","" 2013-04-01 21:40:35.033 UTC,,,26877,,5159fa5f.68fd,2,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint complete: wrote 100635 buffers (2.4%); 0 transaction log file(s) added, 0 removed, 1 recycled; write=539.439 s, sync=0.000 s, total=539.441 s; sync files=0, longest=0.000 s, average=0.000 s","" 2013-04-01 21:41:35.093 UTC,,,26877,,5159fa5f.68fd,3,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint starting: time",""
[PERFORM] Problems with pg_locks explosion
[Apologies, I first sent this to the incorrect list, postgres-admin, in the event you receive it twice] Hi there, I'm hoping someone on the list can shed some light on an issue I'm having with our Postgresql cluster. I'm literally tearing out my hair and don't have a deep enough understanding of Postgres to find the problem. What's happening is I had severe disk/io issues on our original Postgres cluster (9.0.8) and switched to a new instance with a RAID-0 volume array. The machine's CPU usage would hover around 30% and our database would run lightning fast with pg_locks hovering between 100-200. Within a few seconds something would trigger a massive increase in pg_locks so that it suddenly shoots up to 4000-8000. At this point everything dies. Queries that usually take a few milliseconds takes minutes and everything is unresponsive until I restart postgres. The instance still idles at this point. The only clue I could find was that it usually starts a few minutes after the checkpoint entries appear in my logs. Any suggestions would really be appreciated. It's killing our business at the moment. I can supply more info if required but pasted what I thought would be useful below. Not sure what else to change in the settings. Kind regards, Armand It's on Amazon EC2 - * cc2.8xlarge instance type * 6 volumes in RAID-0 configuration. (1000 PIOPS) 60.5 GiB of memory 88 EC2 Compute Units (2 x Intel Xeon E5-2670, eight-core) 3370 GB of instance storage 64-bit platform I/O Performance: Very High (10 Gigabit Ethernet) EBS-Optimized Available: No** API name: cc2.8xlarge postgresql.conf fsync = off full_page_writes = off default_statistics_target = 100 maintenance_work_mem = 1GB checkpoint_completion_target = 0.9 effective_cache_size = 48GB work_mem = 64MB wal_buffers = -1 checkpoint_segments = 128 shared_buffers = 32GB max_connections = 800 effective_io_concurrency = 3 # Down from 6 # - Background Writer - #bgwriter_delay = 200ms # 10-1ms between rounds #bgwriter_lru_maxpages = 100# 0-1000 max buffers written/round #bgwriter_lru_multiplier = 2.0 # 0-10.0 multipler on buffers scanned/round $ free total used free sharedbuffers cached Mem: 61368192 60988180 380012 0784 44167172 -/+ buffers/cache: 16820224 44547968 Swap:0 0 0 $ top -c top - 21:55:51 up 12 days, 12:41, 4 users, load average: 6.03, 16.10, 24.15 top - 21:55:54 up 12 days, 12:41, 4 users, load average: 6.03, 15.94, 24.06 Tasks: 837 total, 6 running, 831 sleeping, 0 stopped, 0 zombie Cpu(s): 15.7%us, 1.7%sy, 0.0%ni, 81.6%id, 0.3%wa, 0.0%hi, 0.6%si, 0.0%st Mem: 61368192k total, 54820988k used, 6547204k free, 9032k buffer [ec2-user@ip-10-155-231-112 ~]$ sudo iostat Linux 3.2.39-6.88.amzn1.x86_64 () 04/01/2013 _x86_64_ (32 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 21.000.001.100.260.00 77.63 Device:tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn xvda 0.21 5.00 2.2254118302401368 xvdk 98.32 1774.67 969.86 1919359965 1048932113 xvdj 98.28 1773.68 969.14 1918288697 1048156776 xvdi 98.29 1773.69 969.61 1918300250 1048662470 xvdh 98.24 1773.92 967.54 1918544618 1046419936 xvdg 98.27 1774.15 968.85 1918790636 1047842846 xvdf 98.32 1775.56 968.69 1920316435 1047668172 md127 733.85 10645.68 5813.70 11513598393 6287682313 What bugs me on this is the throughput percentage on the volumes in Cloudwatch is 100% on all volumes. The problems seem to overlap with checkpoints. 2013-04-01 21:31:35.592 UTC,,,26877,,5159fa5f.68fd,1,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint starting: time","" 2013-04-01 21:40:35.033 UTC,,,26877,,5159fa5f.68fd,2,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint complete: wrote 100635 buffers (2.4%); 0 transaction log file(s) added, 0 removed, 1 recycled; write=539.439 s, sync=0.000 s, total=539.441 s; sync files=0, longest=0.000 s, average=0.000 s","" 2013-04-01 21:41:35.093 UTC,,,26877,,5159fa5f.68fd,3,,2013-04-01 21:21:35 UTC,,0,LOG,0,"checkpoint starting: time",""
