Re: high user cpu, massive SELECTs, no io waiting problem - Mailing list pgsql-performance

Hi,

we are using two instances of pgbouncer v1.4 for connection pooling.
One for prepared statements (pool_mode session) and one without (pool_mode transaction).

Pgbouncer.ini:
[pgbouncer]
pool_mode = transaction/session
server_reset_query = DISCARD ALL;
server_check_query = select 1
server_check_delay = 10
max_client_conn = 10000
default_pool_size = 450
log_connections = 0
log_disconnections = 0
log_pooler_errors = 1
client_login_timeout = 0


I will examine htop next time during a peak.

If I remember correctly vmstat showed lots of context switches during a peak above 50k.

We are running a biweekly downtime where we do a complete reindex and vaccum full. We cannot identify certain queries
causingthis.  

The last graph in ganglia (http://dl.dropbox.com/u/183323/CPUloadprobsdb1.jpg) shows the avg_queries from pgbouncers
stats.I think this is a symptom of many waiting queries which accumulate. 

Our iscsi is connected with 3Gibt/s. But that's more than enough. We don't have high traffic throughput.

This is the result of the query you gave me:

version    PostgreSQL 8.4.4 on x86_64-unknown-linux-gnu, compiled by GCC gcc (Debian 4.3.2-1.1) 4.3.2, 64-bit
checkpoint_segments    40
custom_variable_classes    pg_stat_statements
effective_cache_size    48335MB
escape_string_warning    off
fsync    on
lc_collate    C
lc_ctype    C
listen_addresses    *
log_destination    stderr
log_line_prefix    %t %p %d %u %r
log_lock_waits    on
log_min_duration_statement    1s
log_min_messages    notice
log_rotation_size    10MB
log_temp_files    50MB
logging_collector    on
maintenance_work_mem    1GB
max_connections    1000
max_prepared_transactions    5
max_stack_depth    2MB
pg_stat_statements.max    10000
pg_stat_statements.track    all
port    5433
server_encoding    UTF8
shared_buffers    16GB
TimeZone    Europe/Berlin
update_process_title    on
wal_buffers    1MB
work_mem    32MB


Seems like connection limit 10000 is way too much on pgbouncer? Our queries overall are not that CPU intensive. If they
areslow, they are mostly waiting for disk io. When having a look at the traffic of this database server we see 2/3 of
thetraffic is going to san/disk and only 1/3 going to the server. In other words from the traffic view, 2/3 of our
operationsare writes and 1/3 are reads. The database is fitting completely into ram, so reads should not be a problem. 

Appreciate your help!
Thomas

-----Ursprüngliche Nachricht-----
Von: Kevin Grittner [mailto:Kevin.Grittner@wicourts.gov]
Gesendet: Mittwoch, 16. Februar 2011 17:09
An: Greg Smith; Justin Pitts
Cc: pgsql-performance@postgresql.org; Verteiler_A-Team; Björn Metzdorf; Felix Feinhals; Thomas Pöhler
Betreff: Re: [PERFORM] high user cpu, massive SELECTs, no io waiting problem

Justin Pitts <justinpitts@gmail.com> wrote:
> I think adding
>
> UNION ALL SELECT 'postgres version', version();
>
> might be a good thing.

Good point.  Added.

> Greg Smith <greg@2ndquadrant.com> wrote:
>> Kevin Grittner wrote:
>>>
>>> In fact, I wonder whether we shouldn't leave a couple items
>>> you've excluded, since they are sometimes germane to problems
>>> posted, like lc_collate and TimeZone.
>>
>> I pulled some of them out only because they're not really
>> postgresql.conf settings; lc_collate and lc_ctype for example are
>> set at initdb time.  Feel free to hack on that example if you
>> feel it could be improved, just be aware which of those things
>> are not really in the main config file when pondering if they
>> should be included.

Basically, the ones I could remember us needing to ask about on
multiple occasions, I put back -- provisionally.  If someone thinks
they're pointless, I won't worry about them being dropped again:
time zone, character encoding scheme, character set, and collation.
I'm pretty sure I've seen us ask about all of those in trying to
sort out a problem.

I also tried the query on a newly installed HEAD build which had no
manual changes to the postgresql.conf file and found a few others
which seemed to me to be worth suppressing.

I took my shot -- anyone else is welcome to do so....  :-)

-Kevin