Month: March 2010

Profiling stored procedures/functions

One database that I am monitoring uses a lot of stored procedures. Some of them are fast, some of them are not so fast. I thought – is there a sensible way to diagnose which part of stored procedure take the most time?

I mean – I could just put the logic into application, and then every query would have it's own timing in Pg logs, but this is not practical. And I also believe that using stored procedures/functions is way better than using plain SQL due to a number of reasons.

So, I'm back to question – how to check which part of function takes most of the time?

Continue reading Profiling stored procedures/functions

Setting WAL Replication

There are several approaches on replication/failover – you might have heard of Slony, Londiste, pgPool and some other tools.

WAL Replication is different from all of them in one aspect – it doesn't let you query slave database (until 9.0, in which you actually can run read only queries on slave.

Since you can't run queries on slave, what is it good for? Well. It's good, and great in 1 very important aspect – all things that happen in database are replicated. Schema changes. Sequence modifications. Everything.

There is also drawback – you can't (as of now) replicate just one database. You replicate whole cluster (I don't like this word in this context – let's say: whole installation) of PostgreSQL. All databases that reside in given DATA directory.

So, the question is – how to set it up?

Continue reading Setting WAL Replication

Stupid tricks – Dynamic updates of fields in NEW in PL/pgSQL

Dynamic updates of fields in NEW in PL/pgSQL

Today, on #postgresql on IRC, strk asked about updating fields in NEW record, in plpgsql, but where name of the field is in variable.

After some time, he sent his question to hackers mailing list. And he got prompt reply that it's not possible.

Well, I dare to disagree.

Continue reading Stupid tricks – Dynamic updates of fields in NEW in PL/pgSQL

CHAR(x) vs. VARCHAR(x) vs. VARCHAR vs. TEXT – UPDATED 2010-03-03

UPDATE

Please read also about this change in Pg 9.1, and this change in Pg 9.2 posts, as they explain that since Pg 9.1 some of the limitations listed in this post are no longer there.

END OF UPDATE

Fight!

But more seriously – people tend to use various data types, and there have been some myths about them, so let's see how it really boils down.

First of all – All those data types are internally saved using the same C data structure – varlena.

Thanks to this we can be nearly sure that there are no performance differences. Are there no performance differences in reality? Let's test.

Continue reading CHAR(x) vs. VARCHAR(x) vs. VARCHAR vs. TEXT – UPDATED 2010-03-03