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
>
>
>
>
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