I have limited max connections to 1000, reduced shared buffers to 8G and
restarted postgres.
The logs say that checkpoint finishes in 2,5 minutes (as expected due to
default checkpoint_completion_target = 0.5) with no IO spikes so I don't want
to increase checkpoint_timeout of checkpoint_segments.
I have also noticed that this big tables stopped vacuuming automatically a
couple of weeks ago. It could be the reason of the problem, I will now try to
tune autovacuum parameters to turn it back. But yesterday I ran "vacuum
analyze" for all relations manually but that did not help.
13.02.2014, в 0:14, Ilya Kosmodemiansky <hydrobi...@gmail.com> написал(а):
> On Wed, Feb 12, 2014 at 8:57 PM, Бородин Владимир <r...@simply.name> wrote:
>>
>> Yes, this is legacy, I will fix it. We had lots of inactive connections but
>> right now we use pgbouncer for this. When the workload is normal we have
>> some kind of 80-120 backends. Less than 10 of them are in active state.
>> Having problem with locks we get lots of sessions (sometimes more than 1000
>> of them are in active state). According to vmstat the number of context
>> switches is not so big (less than 20k), so I don't think it is the main
>> reason. Yes, it can aggravate the problem, but imho not create it.
>
>
> I'am afraid that is the problem. More than 1000 backends, most of them
> are simply waiting.
>
>>
>>
>> I don't understand the correlation of shared buffers size and
>> synchronous_commit. Could you please explain your statement?
>
>
> You need to fsync your huge shared buffers any time your database
> performs checkpoint. By default it usually happens too often because
> checkpoint_timeout is 5min by default. Without bbu, on software raid
> that leads to io spike and you commit waits for wal.
>
>
>>
>> 12.02.2014, в 23:37, Ilya Kosmodemiansky <hydrobi...@gmail.com> написал(а):
>>
>> another thing which is arguable - concurrency degree. How many of your
>> max_connections = 4000 are actually running? 4000 definitely looks like an
>> overkill and they could be a serious source of concurrency, especially then
>> you have had barrier enabled and software raid.
>>
>> Plus for 32Gb of shared buffers with synchronous_commit = on especially on
>> heavy workload one should definitely have bbu, otherwise performance will be
>> poor.
>>
>>
>> On Wed, Feb 12, 2014 at 8:20 PM, Бородин Владимир <r...@simply.name> wrote:
>>>
>>> Oh, I haven't thought about barriers, sorry. Although I use soft raid
>>> without batteries I have turned barriers off on one cluster shard to try.
>>>
>>> root@rpopdb01e ~ # mount | fgrep data
>>> /dev/md2 on /var/lib/pgsql/9.3/data type ext4 (rw,noatime,nodiratime)
>>> root@rpopdb01e ~ # mount -o remount,nobarrier /dev/md2
>>> root@rpopdb01e ~ # mount | fgrep data
>>> /dev/md2 on /var/lib/pgsql/9.3/data type ext4
>>> (rw,noatime,nodiratime,nobarrier)
>>> root@rpopdb01e ~ #
>>>
>>> 12.02.2014, в 21:56, Ilya Kosmodemiansky <hydrobi...@gmail.com> написал(а):
>>>
>>> My question was actually about barrier option, by default it is enabled on
>>> RHEL6/ext4 and could cause serious bottleneck on io before disks are
>>> actually involved. What says mount without arguments?
>>>
>>> On Feb 12, 2014, at 18:43, Бородин Владимир <r...@simply.name> wrote:
>>>
>>> root@rpopdb01e ~ # fgrep data /etc/fstab
>>> UUID=f815fd3f-e4e4-43a6-a6a1-bce1203db3e0 /var/lib/pgsql/9.3/data ext4
>>> noatime,nodiratime 0 1
>>> root@rpopdb01e ~ #
>>>
>>> According to iostat the disks are not the bottleneck.
>>>
>>> 12.02.2014, в 21:30, Ilya Kosmodemiansky <hydrobi...@gmail.com> написал(а):
>>>
>>> Hi Vladimir,
>>>
>>> Just in case: how is your ext4 mount?
>>>
>>> Best regards,
>>> Ilya
>>>
>>> On Feb 12, 2014, at 17:59, Бородин Владимир <r...@simply.name> wrote:
>>>
>>> Hi all.
>>>
>>> Today I have started getting errors like below in logs (seems that I have
>>> not changed anything for last week). When it happens the db gets lots of
>>> connections in state active, eats 100% cpu and clients get errors (due to
>>> timeout).
>>>
>>> 2014-02-12 15:44:24.562
>>> MSK,"rpop","rpopdb_p6",30061,"localhost:58350",52fb5e53.756d,1,"SELECT
>>> waiting",2014-02-12 15:43:15 MSK,143/264877,1002850566,LOG,00000,"process
>>> 30061 still waiting for ExclusiveLock on extension of relation 26118 of
>>> database 24590 after 1000.082 ms",,,,,"SQL statement ""insert into
>>> rpop.rpop_imap_uidls (folder_id, uidl) values (i_folder_id, i_uidl)""
>>>
>>> I have read several topics [1, 2, 3, 4] with similar problems but haven't
>>> find a good solution. Below is some more diagnostics.
>>>
>>> I am running PostgreSQL 9.3.2 installed from RPM packages on RHEL 6.4. Host
>>> is running with the following CPU (32 cores) and memory:
>>>
>>> root@rpopdb01e ~ # fgrep -m1 'model name' /proc/cpuinfo
>>> model name : Intel(R) Xeon(R) CPU E5-2660 0 @ 2.20GHz
>>> root@rpopdb01e ~ # free -m
>>> total used free shared buffers cached
>>> Mem: 129028 123558 5469 0 135 119504
>>> -/+ buffers/cache: 3918 125110
>>> Swap: 16378 0 16378
>>> root@rpopdb01e ~ #
>>>
>>> PGDATA lives on RAID6 array of 8 ssd-disks with ext4, iostat and atop say
>>> the disks are really free. Right now PGDATA takes only 95G.
>>> The settings changed in postgresql.conf are here [5].
>>>
>>> When it happens the last query from here [6] shows that almost all queries
>>> are waiting for ExclusiveLock, but they do a simple insert.
>>>
>>> (extend,26647,26825,,,,,,,) | 5459 | ExclusiveLock | 1 |
>>> (extend,26647,26825,,,,,,,) | 8053 | ExclusiveLock | 5459,8053
>>> (extend,26647,26828,,,,,,,) | 5567 | ExclusiveLock | 1 |
>>> (extend,26647,26828,,,,,,,) | 5490 | ExclusiveLock | 5567,5490
>>> (extend,24584,25626,,,,,,,) | 5611 | ExclusiveLock | 1 |
>>> (extend,24584,25626,,,,,,,) | 3963 | ExclusiveLock | 5611,3963
>>>
>>> I have several databases running on one host with one postmaster process
>>> and ExclusiveLock is being waited by many oids. I suppose the only common
>>> thing for all of them is that they are bigger than others and they almost
>>> do not get updates and deletes (only inserts and reads). Some more info
>>> about one of such tables is here [7].
>>>
>>> I have tried to look at the source code (src/backend/access/heap/hio.c) to
>>> understand when the exclusive lock can be taken, but I could only read
>>> comments :) I have also examined FSM for this tables and their indexes and
>>> found that for most of them there are free pages but there are, for
>>> example, such cases:
>>>
>>> rpopdb_p0=# select count(*) from pg_freespace('rpop.rpop_uidl') where avail
>>> != 0;
>>> count
>>> --------
>>> 115953
>>> (1 row)
>>>
>>> rpopdb_p0=# select count(*) from pg_freespace('rpop.pk_rpop_uidl') where
>>> avail != 0;
>>> count
>>> -------
>>> 0
>>> (1 row)
>>>
>>> rpopdb_p0=# \dS+ rpop.rpop_uidl
>>> Table "rpop.rpop_uidl"
>>> Column | Type | Modifiers | Storage | Stats target |
>>> Description
>>> --------+------------------------+-----------+----------+--------------+-------------
>>> popid | bigint | not null | plain | |
>>> uidl | character varying(200) | not null | extended | |
>>> Indexes:
>>> "pk_rpop_uidl" PRIMARY KEY, btree (popid, uidl)
>>> Has OIDs: no
>>>
>>> rpopdb_p0=#
>>>
>>>
>>> My questions are:
>>> 1. Do we consume 100% cpu (in system) trying to get page from FSM? Or does
>>> it happen during exclusive lock acquiring? How can I dig it?
>>> 2. How much space do we extend to the relation when we get exclusive lock
>>> on it?
>>> 3. Why extended page is not visible for other backends?
>>> 4. Is there any possibility of situation where backend A got exclusive lock
>>> on some relation to extend it. Then OS CPU scheduler made a context switch
>>> to backend B while backend B is waiting for exclusive lock on the same
>>> relation. And so on for many backends.
>>> 5. (and the main question) what can I do to get rid of such situations? It
>>> is a production cluster and I do not have any ideas what to do with this
>>> situation :( Any help would be really appropriate.
>>>
>>> [1]
>>> http://www.postgresql.org/message-id/8bca3aa10906011613l8ac2423h8153bbd2513dc...@mail.gmail.com
>>> [2]
>>> http://pgsql.performance.narkive.com/IrkPbl3f/postgresql-9-2-3-performance-problem-caused-exclusive-locks
>>> [3] http://www.postgresql.org/message-id/50a2c93e.9070...@dalibo.com
>>> [4]
>>> http://www.postgresql.org/message-id/cal_0b1sypyeoynkynv95nnv2d+4jxtug3hkkf6fahfw7gvg...@mail.gmail.com
>>> [5] http://pastebin.com/raw.php?i=Bd40Vn6h
>>> [6] http://wiki.postgresql.org/wiki/Lock_dependency_information
>>> [7 http://pastebin.com/raw.php?i=eGrtG524]
>>>
>>> --
>>> Vladimir
>>>
>>>
>>>
>>>
>>>
>>>
>>> --
>>> Vladimir
>>>
>>>
>>>
>>>
>>>
>>>
>>> --
>>> Да пребудет с вами сила...
>>> http://simply.name
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>> --
>> Vladimir
>>
>>
>>
>>
--
Vladimir
