[pgpool-general: 5324] Re: Why pgpool TPS is lowest versus postgresql direct connections?

Sat Feb 11 00:57:37 JST 2017

My immediate thought would be this:  PGPool is much slower with a larger number of concurrent users because some of the connections are being queued by PGPool. Take a look at your num_init_children parameter...unlike most connection pooling layers, PGPool doesn't have separate config parameters for the initial number of backend connections and the max number of backend connections...num_init_children controls both.  Increase num_init_children to at least the number of concurrent connections plus a few, and re-try the benchmark tests.

Also, the benefits of load balancing don't tend to show up well with pgbench or sysbench default benchmarks.  PGPool imposes some overhead in determining which queries can be load-balanced against a standby...with SELECT queries that execute in only a few milliseconds, it might take PGPool longer to make that decision than it would have to just send it straight to the primary. So, you won't see the load balancing benefits with SELECT queries that execute in a few milliseconds, but when you send it SELECT queries that take a few seconds or longer to execute you'll start to see the benefits.  You could create a custom benchmark that has some high-reduction queries that would take a few seconds to execute, then run the benchmarks with that...you should then see scalability improvements from the load balancing.

Hope this helps,

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David Sisk
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From: pgpool-general-bounces at pgpool.net [mailto:pgpool-general-bounces at pgpool.net] On Behalf Of Lazaro Garcia
Sent: Thursday, February 9, 2017 5:00 AM
To: pgpool-general at pgpool.net; pgsql-admin at postgresql.org
Subject: [pgpool-general: 5318] Why pgpool TPS is lowest versus postgresql direct connections?

The correct results reported by sysbench was:

Concurrent Users

1

20

50

100

PostgreSQL

3582

11943

12852

10618

Pgpool

2240

7628

7013

6135

Is there any way to tuning this behavior?

Regards

De: Lazaro Garcia [mailto:lazaro3487 at gmail.com]
Enviado el: miércoles, 8 de febrero de 2017 05:28 p. m.
Para: 'pgpool-general at pgpool.net'; 'pgsql-admin at postgresql.org'
Asunto: Why pgpool TPS is lowest versus postgresql direct connections?

After installed Pgpool with 2 postgresql nodes with streaming replication, I have noticed that access directly to postgresql is more efficient than through pgpool.

I supposed that load balance could increase the transactions per second executed because each node could receive more load, but the results shown below are not expected.

This is the setup:

Pgpool 3.6.1 whit connection pooling, streaming replication mode and load balancing mode.

2 PostgreSQL server 9.6.1 whit streaming replication.

For the tests I used sysbench and pgbench.

The results of sysbench:

Concurrent Users

1

20

50

100

PostgreSQL (TPS) Direct

1166

20936

25743

27344

Pgpool (TPS)

2240

7628

7013

6135

The results of pgbench

1

20

50

100

PostgreSQL (TPS) Direct

1403

6805

6194

5726

Pgpool (TPS)

511

5430

5528

4705

As you can see in both cases even with load balance, the total transactions per second are lower.

Is this the expected behavior. Is there any way to allow more TPS when pgpool is used?

There are other publications with similar results:

https://www.os3.nl/_media/2011-2012/courses/lia/rory_breuk_gerrie_veerman_-_report.pdf    (page 28)
http://www.mail-archive.com/pgpool-general@pgfoundry.org/msg03326.html

Regards
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