Обсуждение: Intermittent hangs with 9.2
Hi All,
I've been seeing a strange issue with our Postgres install for about a year now, and I was hoping someone might be able to help point me at the cause. At what seem like fairly random intervals Postgres will become unresponsive to the 3 application nodes it services. These periods tend to last for 10 - 15 minutes before everything rights itself and the system goes back to normal.
During these periods the server will report a spike in the outbound bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in context switches / interrupts (normal peaks are around 2k/8k respectively, and during these periods they‘ve gone to 15k/22k), and a load average of 100+. CPU usage stays relatively low, but it’s all system time reported, user time goes to zero. It doesn‘t seem to be disk related since we’re running with a shared_buffers setting of 24G, which will fit just about our entire database into memory, and the IO transactions reported by the server, as well as the disk reads reported by Postgres stay consistently low.
We‘ve recently started tracking how long statements take to execute, and we’re seeing some really odd numbers. A simple delete by primary key, for example, from a table that contains about 280,000 rows, reportedly took 18h59m46.900s. An update by primary key in that same table was reported as 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those numbers don't seem reasonable at all.
Some other changes we've made to postgresql.conf:
synchronous_commit = off
maintenance_work_mem = 1GB
wal_level = hot_standby
wal_buffers = 16MB
max_wal_senders = 10
wal_keep_segments = 5000
checkpoint_segments = 128
checkpoint_timeout = 30min
checkpoint_completion_target = 0.9
max_connections = 500
The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of RAM, running Cent OS 6.3.
So far we‘ve tried disabling Transparent Huge Pages after I found a number of resources online that indicated similar interrupt/context switch issues, but it hasn’t resolve the problem. I managed to catch it happening once and run a perf which showed:
+ 41.40% 48154 postmaster 0x347ba9 f 0x347ba9
+ 9.55% 10956 postmaster 0x2dc820 f set_config_option
+ 8.64% 9946 postmaster 0x5a3d4 f writeListPage
+ 5.75% 6609 postmaster 0x5a2b0 f ginHeapTupleFastCollect
+ 2.68% 3084 postmaster 0x192483 f build_implied_join_equality
+ 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR
+ 1.86% 2131 postmaster 0x794aa f get_collation_oid
+ 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert
+ 1.53% 1766 postmaster 0x1929bc f distribute_qual_to_rels
+ 1.33% 1558 postmaster 0x249671 f cmp_numerics
I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a method name.
That's about the sum of it. Any help would be greatly appreciated and if you want any more information about our setup, please feel free to ask.
Thanks,
Dave
On 09/10/2013 11:04 AM, David Whittaker wrote: > > Hi All, > > I've been seeing a strange issue with our Postgres install for about a > year now, and I was hoping someone might be able to help point me at > the cause. At what seem like fairly random intervals Postgres will > become unresponsive to the 3 application nodes it services. These > periods tend to last for 10 - 15 minutes before everything rights > itself and the system goes back to normal. > > During these periods the server will report a spike in the outbound > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike > in context switches / interrupts (normal peaks are around 2k/8k > respectively, and during these periods they‘ve gone to 15k/22k), and a > load average of 100+. CPU usage stays relatively low, but it’s all > system time reported, user time goes to zero. It doesn‘t seem to be > disk related since we’re running with a shared_buffers setting of 24G, > which will fit just about our entire database into memory, and the IO > transactions reported by the server, as well as the disk reads > reported by Postgres stay consistently low. > > We‘ve recently started tracking how long statements take to execute, > and we’re seeing some really odd numbers. A simple delete by primary > key, for example, from a table that contains about 280,000 rows, > reportedly took 18h59m46.900s. An update by primary key in that same > table was reported as 7d 17h 58m 30.415s. That table is frequently > accessed, but obviously those numbers don't seem reasonable at all. > > Some other changes we've made to postgresql.conf: > > synchronous_commit = off > > maintenance_work_mem = 1GB > wal_level = hot_standby > wal_buffers = 16MB > > max_wal_senders = 10 > > wal_keep_segments = 5000 > > checkpoint_segments = 128 > > checkpoint_timeout = 30min > > checkpoint_completion_target = 0.9 > > max_connections = 500 > > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB > of RAM, running Cent OS 6.3. > > So far we‘ve tried disabling Transparent Huge Pages after I found a > number of resources online that indicated similar interrupt/context > switch issues, but it hasn’t resolve the problem. I managed to catch > it happening once and run a perf which showed: > > | > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 > + 9.55% 10956 postmaster 0x2dc820 f set_config_option > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage > + 5.75% 6609 postmaster 0x5a2b0 f ginHeapTupleFastCollect > + 2.68% 3084 postmaster 0x192483 f build_implied_join_equality > + 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR > + 1.86% 2131 postmaster 0x794aa f get_collation_oid > + 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert > + 1.53% 1766 postmaster 0x1929bc f distribute_qual_to_rels > + 1.33% 1558 postmaster 0x249671 f cmp_numerics| > > I‘m not sure what 0x347ba9 represents, or why it’s an address rather > than a method name. > > That's about the sum of it. Any help would be greatly appreciated and > if you want any more information about our setup, please feel free to ask. > > I have seen cases like this with very high shared_buffers settings. 24Gb for shared_buffers is quite high, especially on a 48Gb box. What happens if you dial that back to, say, 12Gb? cheers andrew
On Tue, Sep 10, 2013 at 11:04:21AM -0400, David Whittaker wrote: > Hi All, > > I've been seeing a strange issue with our Postgres install for about a year > now, and I was hoping someone might be able to help point me at the cause. > At what seem like fairly random intervals Postgres will become unresponsive > to the 3 application nodes it services. These periods tend to last for 10 - > 15 minutes before everything rights itself and the system goes back to > normal. > > During these periods the server will report a spike in the outbound > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in > context switches / interrupts (normal peaks are around 2k/8k respectively, > and during these periods they‘ve gone to 15k/22k), and a load average of > 100+. CPU usage stays relatively low, but it’s all system time reported, > user time goes to zero. It doesn‘t seem to be disk related since we’re > running with a shared_buffers setting of 24G, which will fit just about our > entire database into memory, and the IO transactions reported by the > server, as well as the disk reads reported by Postgres stay consistently > low. > > We‘ve recently started tracking how long statements take to execute, and > we’re seeing some really odd numbers. A simple delete by primary key, for > example, from a table that contains about 280,000 rows, reportedly took > 18h59m46.900s. An update by primary key in that same table was reported as > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those > numbers don't seem reasonable at all. > > Some other changes we've made to postgresql.conf: > > synchronous_commit = off > > maintenance_work_mem = 1GB > wal_level = hot_standby > wal_buffers = 16MB > > max_wal_senders = 10 > > wal_keep_segments = 5000 > > checkpoint_segments = 128 > > checkpoint_timeout = 30min > > checkpoint_completion_target = 0.9 > > max_connections = 500 > > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of > RAM, running Cent OS 6.3. > > So far we‘ve tried disabling Transparent Huge Pages after I found a number > of resources online that indicated similar interrupt/context switch issues, > but it hasn’t resolve the problem. I managed to catch it happening once and > run a perf which showed: > > > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 > + 9.55% 10956 postmaster 0x2dc820 f > set_config_option > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage > + 5.75% 6609 postmaster 0x5a2b0 f > ginHeapTupleFastCollect > + 2.68% 3084 postmaster 0x192483 f > build_implied_join_equality > + 2.61% 2990 postmaster 0x187a55 f > build_paths_for_OR > + 1.86% 2131 postmaster 0x794aa f > get_collation_oid > + 1.56% 1822 postmaster 0x5a67e f > ginHeapTupleFastInsert > + 1.53% 1766 postmaster 0x1929bc f > distribute_qual_to_rels > + 1.33% 1558 postmaster 0x249671 f cmp_numerics > > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a > method name. > > That's about the sum of it. Any help would be greatly appreciated and if > you want any more information about our setup, please feel free to ask. > > Thanks, > Dave Hi Dave, A load average of 100+ means that you have that many processes waiting to run yet you only have 16 cpus. You really need to consider using a connection pooler like pgbouncer to keep your connection count in the 16-32 range. Regards, Ken
Hi All,
I've been seeing a strange issue with our Postgres install for about a year now, and I was hoping someone might be able to help point me at the cause. At what seem like fairly random intervals Postgres will become unresponsive to the 3 application nodes it services. These periods tend to last for 10 - 15 minutes before everything rights itself and the system goes back to normal.
During these periods the server will report a spike in the outbound bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in context switches / interrupts (normal peaks are around 2k/8k respectively, and during these periods they‘ve gone to 15k/22k), and a load average of 100+.
CPU usage stays relatively low, but it’s all system time reported, user time goes to zero. It doesn‘t seem to be disk related since we’re running with a shared_buffers setting of 24G, which will fit just about our entire database into memory, and the IO transactions reported by the server, as well as the disk reads reported by Postgres stay consistently low.
We‘ve recently started tracking how long statements take to execute, and we’re seeing some really odd numbers. A simple delete by primary key, for example, from a table that contains about 280,000 rows, reportedly took 18h59m46.900s. An update by primary key in that same table was reported as 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those numbers don't seem reasonable at all.
On Tue, Sep 10, 2013 at 10:04 AM, David Whittaker <dave@iradix.com> wrote: > Hi All, > > I've been seeing a strange issue with our Postgres install for about a year > now, and I was hoping someone might be able to help point me at the cause. > At what seem like fairly random intervals Postgres will become unresponsive > to the 3 application nodes it services. These periods tend to last for 10 - > 15 minutes before everything rights itself and the system goes back to > normal. > > During these periods the server will report a spike in the outbound > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in > context switches / interrupts (normal peaks are around 2k/8k respectively, > and during these periods they‘ve gone to 15k/22k), and a load average of > 100+. CPU usage stays relatively low, but it’s all system time reported, > user time goes to zero. It doesn‘t seem to be disk related since we’re > running with a shared_buffers setting of 24G, which will fit just about our > entire database into memory, and the IO transactions reported by the server, > as well as the disk reads reported by Postgres stay consistently low. > > We‘ve recently started tracking how long statements take to execute, and > we’re seeing some really odd numbers. A simple delete by primary key, for > example, from a table that contains about 280,000 rows, reportedly took > 18h59m46.900s. An update by primary key in that same table was reported as > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those > numbers don't seem reasonable at all. > > Some other changes we've made to postgresql.conf: > > synchronous_commit = off > > maintenance_work_mem = 1GB > wal_level = hot_standby > wal_buffers = 16MB > > max_wal_senders = 10 > > wal_keep_segments = 5000 > > checkpoint_segments = 128 > > checkpoint_timeout = 30min > > checkpoint_completion_target = 0.9 > > max_connections = 500 > > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of > RAM, running Cent OS 6.3. > > So far we‘ve tried disabling Transparent Huge Pages after I found a number > of resources online that indicated similar interrupt/context switch issues, > but it hasn’t resolve the problem. I managed to catch it happening once and > run a perf which showed: > > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 > + 9.55% 10956 postmaster 0x2dc820 f set_config_option > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage > + 5.75% 6609 postmaster 0x5a2b0 f > ginHeapTupleFastCollect > + 2.68% 3084 postmaster 0x192483 f > build_implied_join_equality > + 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR > + 1.86% 2131 postmaster 0x794aa f get_collation_oid > + 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert > + 1.53% 1766 postmaster 0x1929bc f > distribute_qual_to_rels > + 1.33% 1558 postmaster 0x249671 f cmp_numerics > > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a > method name. > > That's about the sum of it. Any help would be greatly appreciated and if you > want any more information about our setup, please feel free to ask. Reducing shared buffers to around 2gb will probably make the problem go away *) What's your ratio reads to writes (approximately)? *) How many connections when it happens. Do connections pile on after that? *) Are you willing to run custom patched postmaster to help troubleshoot the problem? merlin
On 2013-09-11 07:43:35 -0500, Merlin Moncure wrote: > > I've been seeing a strange issue with our Postgres install for about a year > > now, and I was hoping someone might be able to help point me at the cause. > > At what seem like fairly random intervals Postgres will become unresponsive > > to the 3 application nodes it services. These periods tend to last for 10 - > > 15 minutes before everything rights itself and the system goes back to > > normal. > > > > During these periods the server will report a spike in the outbound > > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in > > context switches / interrupts (normal peaks are around 2k/8k respectively, > > and during these periods they‘ve gone to 15k/22k), and a load average of > > 100+. CPU usage stays relatively low, but it’s all system time reported, > > user time goes to zero. It doesn‘t seem to be disk related since we’re > > running with a shared_buffers setting of 24G, which will fit just about our > > entire database into memory, and the IO transactions reported by the server, > > as well as the disk reads reported by Postgres stay consistently low. > > > > We‘ve recently started tracking how long statements take to execute, and > > we’re seeing some really odd numbers. A simple delete by primary key, for > > example, from a table that contains about 280,000 rows, reportedly took > > 18h59m46.900s. An update by primary key in that same table was reported as > > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those > > numbers don't seem reasonable at all. > > > > Some other changes we've made to postgresql.conf: > > > > synchronous_commit = off > > > > maintenance_work_mem = 1GB > > wal_level = hot_standby > > wal_buffers = 16MB > > > > max_wal_senders = 10 > > > > wal_keep_segments = 5000 > > > > checkpoint_segments = 128 > > > > checkpoint_timeout = 30min > > > > checkpoint_completion_target = 0.9 > > > > max_connections = 500 > > > > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of > > RAM, running Cent OS 6.3. > > > > So far we‘ve tried disabling Transparent Huge Pages after I found a number > > of resources online that indicated similar interrupt/context switch issues, > > but it hasn’t resolve the problem. I managed to catch it happening once and > > run a perf which showed: > > > > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 > > + 9.55% 10956 postmaster 0x2dc820 f set_config_option > > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage > > + 5.75% 6609 postmaster 0x5a2b0 f > > ginHeapTupleFastCollect > > + 2.68% 3084 postmaster 0x192483 f > > build_implied_join_equality > > + 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR > > + 1.86% 2131 postmaster 0x794aa f get_collation_oid > > + 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert > > + 1.53% 1766 postmaster 0x1929bc f > > distribute_qual_to_rels > > + 1.33% 1558 postmaster 0x249671 f cmp_numerics > > > > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a > > method name. Try converting it to something more meaningful with "addr2line", that often has more sucess. > > That's about the sum of it. Any help would be greatly appreciated and if you > > want any more information about our setup, please feel free to ask. > Reducing shared buffers to around 2gb will probably make the problem go away That profile doesn't really look like one of the problem you are referring to would look like. Based on the profile I'd guess it's possible that you're seing problems with GIN's "fastupdate" mechanism. Try ALTER INDEX whatever SET (FASTUPDATE = OFF); VACUUM whatever's_table for all gin indexes. It's curious that set_config_option is so high in the profile... Any chance you could recompile postgres with -fno-omit-frame-pointers in CFLAGS? That would allow you to use perf -g. The performance price of that usually is below 1% for postgres. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
On Wed, Sep 11, 2013 at 12:17 PM, Andres Freund <andres@2ndquadrant.com> wrote: > On 2013-09-11 07:43:35 -0500, Merlin Moncure wrote: >> > I've been seeing a strange issue with our Postgres install for about a year >> > now, and I was hoping someone might be able to help point me at the cause. >> > At what seem like fairly random intervals Postgres will become unresponsive >> > to the 3 application nodes it services. These periods tend to last for 10 - >> > 15 minutes before everything rights itself and the system goes back to >> > normal. >> > >> > During these periods the server will report a spike in the outbound >> > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in >> > context switches / interrupts (normal peaks are around 2k/8k respectively, >> > and during these periods they‘ve gone to 15k/22k), and a load average of >> > 100+. CPU usage stays relatively low, but it’s all system time reported, >> > user time goes to zero. It doesn‘t seem to be disk related since we’re >> > running with a shared_buffers setting of 24G, which will fit just about our >> > entire database into memory, and the IO transactions reported by the server, >> > as well as the disk reads reported by Postgres stay consistently low. >> > >> > We‘ve recently started tracking how long statements take to execute, and >> > we’re seeing some really odd numbers. A simple delete by primary key, for >> > example, from a table that contains about 280,000 rows, reportedly took >> > 18h59m46.900s. An update by primary key in that same table was reported as >> > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those >> > numbers don't seem reasonable at all. >> > >> > Some other changes we've made to postgresql.conf: >> > >> > synchronous_commit = off >> > >> > maintenance_work_mem = 1GB >> > wal_level = hot_standby >> > wal_buffers = 16MB >> > >> > max_wal_senders = 10 >> > >> > wal_keep_segments = 5000 >> > >> > checkpoint_segments = 128 >> > >> > checkpoint_timeout = 30min >> > >> > checkpoint_completion_target = 0.9 >> > >> > max_connections = 500 >> > >> > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of >> > RAM, running Cent OS 6.3. >> > >> > So far we‘ve tried disabling Transparent Huge Pages after I found a number >> > of resources online that indicated similar interrupt/context switch issues, >> > but it hasn’t resolve the problem. I managed to catch it happening once and >> > run a perf which showed: >> > >> > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 >> > + 9.55% 10956 postmaster 0x2dc820 f set_config_option >> > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage >> > + 5.75% 6609 postmaster 0x5a2b0 f >> > ginHeapTupleFastCollect >> > + 2.68% 3084 postmaster 0x192483 f >> > build_implied_join_equality >> > + 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR >> > + 1.86% 2131 postmaster 0x794aa f get_collation_oid >> > + 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert >> > + 1.53% 1766 postmaster 0x1929bc f >> > distribute_qual_to_rels >> > + 1.33% 1558 postmaster 0x249671 f cmp_numerics >> > >> > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a >> > method name. > > Try converting it to something more meaningful with "addr2line", that > often has more sucess. > >> > That's about the sum of it. Any help would be greatly appreciated and if you >> > want any more information about our setup, please feel free to ask. > >> Reducing shared buffers to around 2gb will probably make the problem go away > > That profile doesn't really look like one of the problem you are > referring to would look like. yup -- I think you're right. merlin
Try converting it to something more meaningful with "addr2line", thatOn 2013-09-11 07:43:35 -0500, Merlin Moncure wrote:
> > I've been seeing a strange issue with our Postgres install for about a year
> > now, and I was hoping someone might be able to help point me at the cause.
> > At what seem like fairly random intervals Postgres will become unresponsive
> > to the 3 application nodes it services. These periods tend to last for 10 -
> > 15 minutes before everything rights itself and the system goes back to
> > normal.
> >
> > During these periods the server will report a spike in the outbound
> > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in
> > context switches / interrupts (normal peaks are around 2k/8k respectively,
> > and during these periods they‘ve gone to 15k/22k), and a load average of
> > 100+. CPU usage stays relatively low, but it’s all system time reported,
> > user time goes to zero. It doesn‘t seem to be disk related since we’re
> > running with a shared_buffers setting of 24G, which will fit just about our
> > entire database into memory, and the IO transactions reported by the server,
> > as well as the disk reads reported by Postgres stay consistently low.
> >
> > We‘ve recently started tracking how long statements take to execute, and
> > we’re seeing some really odd numbers. A simple delete by primary key, for
> > example, from a table that contains about 280,000 rows, reportedly took
> > 18h59m46.900s. An update by primary key in that same table was reported as
> > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those
> > numbers don't seem reasonable at all.
> >
> > Some other changes we've made to postgresql.conf:
> >
> > synchronous_commit = off
> >
> > maintenance_work_mem = 1GB
> > wal_level = hot_standby
> > wal_buffers = 16MB
> >
> > max_wal_senders = 10
> >
> > wal_keep_segments = 5000
> >
> > checkpoint_segments = 128
> >
> > checkpoint_timeout = 30min
> >
> > checkpoint_completion_target = 0.9
> >
> > max_connections = 500
> >
> > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of
> > RAM, running Cent OS 6.3.
> >
> > So far we‘ve tried disabling Transparent Huge Pages after I found a number
> > of resources online that indicated similar interrupt/context switch issues,
> > but it hasn’t resolve the problem. I managed to catch it happening once and
> > run a perf which showed:
> >
> > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9
> > + 9.55% 10956 postmaster 0x2dc820 f set_config_option
> > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage
> > + 5.75% 6609 postmaster 0x5a2b0 f
> > ginHeapTupleFastCollect
> > + 2.68% 3084 postmaster 0x192483 f
> > build_implied_join_equality
> > + 2.61% 2990 postmaster 0x187a55 f build_paths_for_OR
> > + 1.86% 2131 postmaster 0x794aa f get_collation_oid
> > + 1.56% 1822 postmaster 0x5a67e f ginHeapTupleFastInsert
> > + 1.53% 1766 postmaster 0x1929bc f
> > distribute_qual_to_rels
> > + 1.33% 1558 postmaster 0x249671 f cmp_numerics
> >
> > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a
> > method name.
often has more sucess.That profile doesn't really look like one of the problem you are
> > That's about the sum of it. Any help would be greatly appreciated and if you
> > want any more information about our setup, please feel free to ask.
> Reducing shared buffers to around 2gb will probably make the problem go away
referring to would look like.
Based on the profile I'd guess it's possible that you're seing problems
with GIN's "fastupdate" mechanism.
Try ALTER INDEX whatever SET (FASTUPDATE = OFF); VACUUM
whatever's_table for all gin indexes.
It's curious that set_config_option is so high in the profile... Any
chance you could recompile postgres with -fno-omit-frame-pointers in
CFLAGS? That would allow you to use perf -g. The performance price of
that usually is below 1% for postgres.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
On Thu, Sep 12, 2013 at 3:06 PM, David Whittaker <dave@iradix.com> wrote: > Hi All, > > We lowered shared_buffers to 8G and increased effective_cache_size > accordingly. So far, we haven't seen any issues since the adjustment. The > issues have come and gone in the past, so I'm not convinced it won't crop up > again, but I think the best course is to wait a week or so and see how > things work out before we make any other changes. > > Thank you all for your help, and if the problem does reoccur, we'll look > into the other options suggested, like using a patched postmaster and > compiling for perf -g. > > Thanks again, I really appreciate the feedback from everyone. Interesting -- please respond with a follow up if/when you feel satisfied the problem has gone away. Andres was right; I initially mis-diagnosed the problem (there is another issue I'm chasing that has a similar performance presentation but originates from a different area of the code). That said, if reducing shared_buffers made *your* problem go away as well, then this more evidence that we have an underlying contention mechanic that is somehow influenced by the setting. Speaking frankly, under certain workloads we seem to have contention issues in the general area of the buffer system. I'm thinking (guessing) that the problems is usage_count is getting incremented faster than the buffers are getting cleared out which is then causing the sweeper to spend more and more time examining hotly contended buffers. This may make no sense in the context of your issue; I haven't looked at the code yet. Also, I've been unable to cause this to happen in simulated testing. But I'm suspicious (and dollars to doughnuts '0x347ba9' is spinlock related). Anyways, thanks for the report and (hopefully) the follow up. merlin
On Thu, Sep 12, 2013 at 3:06 PM, David Whittaker <dave@iradix.com> wrote:Interesting -- please respond with a follow up if/when you feel
> Hi All,
>
> We lowered shared_buffers to 8G and increased effective_cache_size
> accordingly. So far, we haven't seen any issues since the adjustment. The
> issues have come and gone in the past, so I'm not convinced it won't crop up
> again, but I think the best course is to wait a week or so and see how
> things work out before we make any other changes.
>
> Thank you all for your help, and if the problem does reoccur, we'll look
> into the other options suggested, like using a patched postmaster and
> compiling for perf -g.
>
> Thanks again, I really appreciate the feedback from everyone.
satisfied the problem has gone away. Andres was right; I initially
mis-diagnosed the problem (there is another issue I'm chasing that has
a similar performance presentation but originates from a different
area of the code).
That said, if reducing shared_buffers made *your* problem go away as
well, then this more evidence that we have an underlying contention
mechanic that is somehow influenced by the setting. Speaking frankly,
under certain workloads we seem to have contention issues in the
general area of the buffer system. I'm thinking (guessing) that the
problems is usage_count is getting incremented faster than the buffers
are getting cleared out which is then causing the sweeper to spend
more and more time examining hotly contended buffers. This may make
no sense in the context of your issue; I haven't looked at the code
yet. Also, I've been unable to cause this to happen in simulated
testing. But I'm suspicious (and dollars to doughnuts '0x347ba9' is
spinlock related).
Anyways, thanks for the report and (hopefully) the follow up.
merlin
On Fri, Sep 13, 2013 at 10:52 AM, Merlin Moncure <mmoncure@gmail.com> wrote:On Thu, Sep 12, 2013 at 3:06 PM, David Whittaker <dave@iradix.com> wrote:Interesting -- please respond with a follow up if/when you feel
> Hi All,
>
> We lowered shared_buffers to 8G and increased effective_cache_size
> accordingly. So far, we haven't seen any issues since the adjustment. The
> issues have come and gone in the past, so I'm not convinced it won't crop up
> again, but I think the best course is to wait a week or so and see how
> things work out before we make any other changes.
>
> Thank you all for your help, and if the problem does reoccur, we'll look
> into the other options suggested, like using a patched postmaster and
> compiling for perf -g.
>
> Thanks again, I really appreciate the feedback from everyone.
satisfied the problem has gone away. Andres was right; I initially
mis-diagnosed the problem (there is another issue I'm chasing that has
a similar performance presentation but originates from a different
area of the code).
That said, if reducing shared_buffers made *your* problem go away as
well, then this more evidence that we have an underlying contention
mechanic that is somehow influenced by the setting. Speaking frankly,
under certain workloads we seem to have contention issues in the
general area of the buffer system. I'm thinking (guessing) that the
problems is usage_count is getting incremented faster than the buffers
are getting cleared out which is then causing the sweeper to spend
more and more time examining hotly contended buffers. This may make
no sense in the context of your issue; I haven't looked at the code
yet. Also, I've been unable to cause this to happen in simulated
testing. But I'm suspicious (and dollars to doughnuts '0x347ba9' is
spinlock related).
Anyways, thanks for the report and (hopefully) the follow up.
merlinYou guys have taken the time to help me through this, following up is the least I can do. So far we're still looking good.