[pgpool-general: 1556] Re: pgpool 3.2.3 node gets down after some hours of work.

Lonni J Friedman netllama at gmail.com
Fri Mar 29 10:07:28 JST 2013

On Thu, Mar 28, 2013 at 6:00 PM, Dzmitry <dzmitry.nikitsin at gmail.com> wrote:
> I don't see any network latency and we are not sending a lot of data. I
> don't know how big is delay in replication, but delay exists - it's how
> streaming replication works.

A small delay of less than 1 second is how it should work.  You
haven't quantified what kind of delaying you're experiencing, however
if its many seconds (or more), then something is most definitely not
right in your environment, and you need to determine what it is and
attempt to resolve it.

Are the servers identical in both software & hardware?
Is the replication latency a fixed amount?

> If  I do almost simultaneous 2 sql query, one to write data, second - read
> written data. Does pgpool handle this situation and do write/read from
> master DB(if yes - does delay is configurable?) ? Or it can write to
> master and read from slave - when data is not synchronized.

The percentage of read query distributions is determined by how you
configured pgpool.  However, again, if your data is non-trivially
unsynchronized, then you need to understand & rectify that problem.
Hacking around it in pgpool is not a viable solution, especially in a
production environment, where I assume you want your data to be
consistent at all times.

> Thanks,
>   Dzmitry
> On 3/29/13 3:53 AM, "Lonni J Friedman" <netllama at gmail.com> wrote:
>>I think you're trying to solve the wrong problem.   Something seems
>>wrong in your environment if there's a non-trivial delay in
>>replication between the master & standby.  Is the standby struggling
>>to keep up with the changes, or is there a lot of network latency, or
>>is there some other problem?
>>On Thu, Mar 28, 2013 at 4:48 PM, Dzmitry <dzmitry.nikitsin at gmail.com>
>>> I installed & configured pgpool using this guide
>>> http://www.pgpool.net/pgpool-web/contrib_docs/simple_sr_setting2_3.0/ .
>>> But I found issue with log - you made me thinking, thank you. The issue
>>> was I haven't /usr/sbin/rotatelogs2 but I have /usr/sbin/rotatelogs.
>>> I will monitor log to check why my node goes down.
>>> One more question - my production application is connected to pgpool &
>>> do load balancing. When application write data - pgpool send queries to
>>> master DB & master do streaming replication with delay. But application
>>> can do read very quickly - and pgpool can send query to standy DB where
>>> changes is not synchronized yet.(for example user signup: 1 signup, 2 -
>>> show protected page - here data can be not synchronized). Is it possible
>>> to resolve this situation with pgpool somehow ? Does it have option to
>>> send query to specified DB ? Or I need to connect my production
>>> application server to master DB directly, but servers that do background
>>> processing - can be connected to pgpool ?
>>> Thanks,
>>>   Dzmitry
>>> On 3/29/13 2:24 AM, "Lonni J Friedman" <netllama at gmail.com> wrote:
>>>>On Thu, Mar 28, 2013 at 4:10 PM, Dzmitry <dzmitry.nikitsin at gmail.com>
>>>>> Dear all,
>>>>> I am using postgres 9.2 with streaming replication. I have 1 master DB
>>>>> 2 standby DBs, it's hosted on amazon EC2, each has it's own server. On
>>>>> separate server i have pgpool(3.2.3) that do load balancing(in pgpool
>>>>> config i have num_init_children=290, max_pool- 2, child_life_time -
>>>>> 0child_max_connections - 100, connection_life_time- 100,
>>>>> - 0. do not cache onnections.). Sometimes pgpool show server status as
>>>>> "down", but actually server is up & running fine, due to this, i am
>>>>> getting a lot of issues.
>>>>> Also i have in pgpool config:
>>>>> health_check_timeout - 60
>>>>> health_check_period - 30
>>>>> health_check_max_retries - 3
>>>>> health_check_retry_delay -5
>>>>> Also pgpool is not writing log :(
>>>>> i setup it
>>>>> log_destination "stderr"
>>>>> debug_level 0
>>>>> logdir /var/tmp - i checked permissions it has 777, so it's not the
>>>>> when i start pgpool i start it with "-n" option to let it write log.
>>>>> Any ideas why server shown as down & where is my logs ?
>>>>Your logs would indicate why the nodes are down.  As for where they
>>>>are, you'd have to tell us.  How did you install & configure pgpool?

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