[Pgpool-hackers] worker process launch even when health_check_period=0

[Guillaume Lelarge]

On 05/23/2011 03:59 PM, Tatsuo Ishii wrote:
>> Le 05/23/2011 03:02 PM, Tatsuo Ishii a écrit :
>>>> AFAICT, the worker process has one work to do: check replication lag.
>>>> pgPool only needs to check replication lag if we are using streaming
>>>> replication and if health check is enabled. However, it seems it checks
>>>> replication lag even if health check is disabled (with
>>>> health_check_period=0).
>>>>
>>>> This looks like a bug to me.
>>>>
>>>> I see two fixes:
>>>>   * only launch the worker process if health_check_period>0 (main.c)
>>>>   * before checking lag, make sure that health_check_period>0
>>>>     (pool_worker_child.c)
>>>>
>>>> I can write the patch, it won't be difficult. Just want to make sure
>>>> you're OK with this and that I didn't miss something.
>>>
>>> People might want to check replication delay even if they are not
>>> using health check, no?
>>
>> Sure. They might want. If we say so, we shouldn't say otherwise in the
>> docs ("If delay_threshold is 0 or health checking is disabled, the delay
>> checking is not performed.") Moreover, I don't see why the worker should
>> sleep 30+health_check_period.
> 
> Not really. sleep 30 only happens when health_check_period <= 0.
> 

Oh yeah, you're right.

>> And last one, it's kind of weird to
>> disable helath-check but still use health_user to check the replication lag.
>>
>> Maybe we should use the worker for different kinds of checks:
>> replication lag, health, others?
> 
> Yes, I think we'd better to have "delay_check_period" or some such.
> 

Well, if we use different period of time, it'll get harder and harder to
understand each part. I think it would be better to have a
worker_naptime, worker_user (they would replace health_check_period and
health_check_user). But we would keep health_check_timeout, and
delay_threshold. And both activities would take place in the worker
process. But this is more 3.1, or even 3.2 material.

>> Anyway, right now, we have one main issue. We say in the docs that
>> replication lag is disabled if health_check is disabled, but the code
>> doesn't do that. At least one of them should be fixed. And I think we
>> need to fix the code.
> 
> Oops. You are right. We should fix the code.
> 
> BTW, this part:
>>>>   * only launch the worker process if health_check_period>0 (main.c)
> 
> If we want to do:
> 
> If delay_threshold/health_check_period set to greater than 0 and
> pgpool.conf is reloaded, I would like to see delay checking starts.
> Like wise, if delay_threshold/health_check_period is set to 0 and
> pgpool.conf reloded, we need to stop worker process.
> 
> Probably it's lot easier to always start worker process right now,
> just check those variables in the process.

Completely agree. I didn't think about configuration reloading, and
you're completely right: it's better to launch the worker, it makes it
more simple to handle configuration reloading.

Working on a patch to fix the issue in 3.0.


-- 
Guillaume
 http://www.postgresql.fr
 http://dalibo.com