Thread: Too much clients connected to the PostgreSQL Database

Rodrigo Pereira da Silva wrote:

> We have about 10 web applications deployed in a Tomcat 7.0
> accessing a Postgresql 9.1 database. We do use connection pooling.
> We have the max_connections parameter set to 200 connections,
> however, we are reaching the max connections sporadically(about 4
> time/day).

What is the pooler's maxActive setting? (It should be less than the
PostgreSQL max_connections setting.)

BTW, 200 seems alwfully high unless a *really* high end machine.  You
may have fewer timeouts if you avoid swamping the server with a
"thundering herd" of requests.

http://wiki.postgresql.org/wiki/Number_Of_Database_Connections

-Kevin

150 maxActive setting, but we have some low usage application getting direct db
connection(out of the pool).

The interesting is that the server suddently get a lot of connections and reach the
limit and then release them.

I'm willing to change to Tomcat 7 connection pool. We are using c3pO and apache ones,
maybe that's a problem.

Thank you,

Well,

> Rodrigo Pereira da Silva wrote:
>
>> We have about 10 web applications deployed in a Tomcat 7.0
>> accessing a Postgresql 9.1 database. We do use connection pooling.
>> We have the max_connections parameter set to 200 connections,
>> however, we are reaching the max connections sporadically(about 4
>> time/day).
>
> What is the pooler's maxActive setting? (It should be less than the
> PostgreSQL max_connections setting.)
>
> BTW, 200 seems alwfully high unless a *really* high end machine.  You
> may have fewer timeouts if you avoid swamping the server with a
> "thundering herd" of requests.
>
> http://wiki.postgresql.org/wiki/Number_Of_Database_Connections
>
> -Kevin
>
>
> --
> Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-general
>

rodrigo@paripassu.com.br wrote:

> 150 maxActive setting, but we have some low usage application
> getting direct db connection(out of the pool).

You will probably be better off with a connection pool somewhere
between 10 and 20, as long as it is transaction-based, the client
side has low latency to the database, and the transaction isn't
waiting for other things (like human beings or slow connections to
somewhere else) to get its work done.

> The interesting is that the server suddently get a lot of
> connections and reach the limit and then release them.

That is the pattern you will tend to see if you have too many
configured. The "thundering herd" syndrome. They charge in, drag
down performance while they over-stress the hardware, and then move
on.

> I'm willing to change to Tomcat 7 connection pool. We are using
> c3pO and apache ones, maybe that's a problem.

I have seen both the Tomcat pool and DBCP work well, although I think
the DBCP pool has more features. I don't have enough experience with
c3p0 to comment either way. I definitely would not bother to move
from Apache DBCP to the Tomcat pool. If I remember right I didn't
find much worth changing from defaults in the DBCP package, but it's
been a while. I would recommend either of those over an external
product like pgbouncer or pgpool; those are what you go to when you
don't have a quality connection pooler in your application software,
IMO.

The point is to configure whatever pool you use to limit the number
of active database transactions such that the active connections are
able to keep all available resources on the database server (cores,
spindles, network) busy, but no more. That should improve both
latency and throughput. There is no substitute for testing different
sizes with your actual load against your actual hardware; any advice
on size should be taken as the starting point for testing incremental
changes.

-Kevin

Am 30.10.2012 02:06, schrieb rodrigo@paripassu.com.br:
> BTW, 200 seems alwfully high unless a *really* high end machine. Â You
>> may have fewer timeouts if you avoid swamping the server with a
>> "thundering herd" of requests.

I was maintaining a setup which had > 1000 connections on a not very
high-end server (12GB of Ram). It was just most of the connections were
idling most the time. Tomcat with a high number of consistent
connections for some reasons and end user stand alone clients which are
establishing a database connection on startup and keeping them until
shutdown.

Cheers,
Frank

On 10/30/12 12:32 AM, Frank Lanitz wrote:
> I was maintaining a setup which had > 1000 connections on a not very
> high-end server (12GB of Ram). It was just most of the connections were
> idling most the time. Tomcat with a high number of consistent
> connections for some reasons and end user stand alone clients which are
> establishing a database connection on startup and keeping them until
> shutdown.

a better configuration for that is for your web applications to grab a
connection from a connection pool, do a transaction, and then release
the connection as soon as you are done.   keep the pool size modest,
maybe 2-4X the number of CPU cores you have.   IF you have some things
that do long running queries, like for calculating reports, create a
separate smaller pool for these as there likely are only 1-2 of them at
a time anyways.



--
john r pierce                            N 37, W 122
santa cruz ca                         mid-left coast

rodrigo@paripassu.com.br wrote:

150 maxActive setting, but we have some low usage application
getting direct db connection(out of the pool).

You will probably be better off with a connection pool somewhere
between 10 and 20, as long as it is transaction-based, the client
side has low latency to the database, and the transaction isn't
waiting for other things (like human beings or slow connections to
somewhere else) to get its work done.

The interesting is that the server suddently get a lot of
connections and reach the limit and then release them.

That is the pattern you will tend to see if you have too many
configured. The "thundering herd" syndrome. They charge in, drag
down performance while they over-stress the hardware, and then move
on.

I'm willing to change to Tomcat 7 connection pool. We are using
c3pO and apache ones, maybe that's a problem.

I have seen both the Tomcat pool and DBCP work well, although I think
the DBCP pool has more features. I don't have enough experience with
c3p0 to comment either way. I definitely would not bother to move
from Apache DBCP to the Tomcat pool. If I remember right I didn't
find much worth changing from defaults in the DBCP package, but it's
been a while. I would recommend either of those over an external
product like pgbouncer or pgpool; those are what you go to when you
don't have a quality connection pooler in your application software,
IMO.

The point is to configure whatever pool you use to limit the number
of active database transactions such that the active connections are
able to keep all available resources on the database server (cores,
spindles, network) busy, but no more. That should improve both
latency and throughput. There is no substitute for testing different
sizes with your actual load against your actual hardware; any advice
on size should be taken as the starting point for testing incremental
changes.

-Kevin

--

Rodrigo Pereira da Silva rodrigo@paripassu.com.br http://www.paripassu.com.br Rua Coronel Luis Caldeira, nº 67, Bloco 1, Sala 3A 88034-110 • Florianópolis • SC Tel. (48) 3207-5755