What logging has least overhead?

When working with PostgreSQL you generally want to get information about slow queries. The usual approach is to set log_min_duration_statement to some low(ish) value, run your app, and then analyze logs.

But you can log to many places – flat file, flat file on another disk, local syslog, remote syslog. And – perhaps, instead of log_min_duration_statement – just use pg_stat_statements?

Well, I wondered about it, and decided to test.

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Understanding postgresql.conf : log*

After loooong pause, adding next (well, second) post to the “series“. This time, I'd like to describe how logging works. And I don't mean binary logging (WAL), but the log for us, humans, to read.

Before I will go to the postgresql.conf options, let me first describe what happens when PostgreSQL wants to log something.

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Logging queries – how?

One of the questions that pop up frequently on IRC is how to see queries are now executed on the server, and what queries were earlier.

Theoretically answer to this is simple – pg_stat_activity and log_min_duration_statement. Or log_statement. What is the difference? That's exactly why I'm writing this post.

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