Russ Brown wrote:
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> Not long back I switched from the prefork apache MPM to the worker one,
> at the suggestion of coderanger (due to better memory efficiency etc). I
> set it up to run on two processes each spawning a number of threads.
>
> Yesterday we encountered Trac being unable to connect to the database
> (Postgres 8.2, Trac 0.11 RC2), and when investigating it noticed that
> trac only had two connections open (two large requests were being
> processed at this time leading to the site being unavailable to other
> requests).
>   

This problem won't be solved by the new pool code, which doesn't prevent 
long running requests to block others.
In some cases, we hold a db connection for too long with no good reason, 
and this is likely the problem you had here.

For example, I have a very big test changeset and while it's being 
loaded, I can't make other requests which want to save something in the 
db (even session related data, like for login/logout, timeline views, 
query updates). This is not optimal, as there's no reason a db 
connection should be kept alive during that processing. I've seen this 
with SQLite and I've not yet tried to reproduce this with PostgreSQL.

> I asked about this in IRC and was told that there were issues with the
> pooling in RC2 and that I should upgrade to 0.11. coderanger also
> mentioned the TRAC_DB_POOL_SIZE environment variable which could be used
> to control the connection pooling.
>
> I did that, but Trac still only held two connections open. I viewed
> trac/db/pool.py and saw no mention of TRAC_DB_POOL_SIZE. Looking at the
> file on trunk (of t.e.o) I do see it there, which suggests that
> TRAC_DB_POOL_SIZE was actually added post 0.11. I also don't see it in
> that file on the 0.11-stable branch.
>
> Is there any estimate as to when this change might be released (e.g.
> 0.11.1)?
>   

I didn't have problems with the new pool so far, neither did we receive 
any bug report from trunk users, so I think it's safe to backport it to 
0.11-stable in the coming days.

-- Christian


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