3 November 2016
2 November 2016
The slides for my presentation Unclogging the VACUUM at PGConf EU in Tallinn, Estonia are now available.
4 June 2016
16 February 2016
Everyone has their own style, unfortunately, on how they edit postgresql.conf. Some like to uncomment specific values and edit them at the point they appear in the default file, some like to tack overrides onto the end… and some do a mixture of those (don’t do that).
My personal preference is to leave everything in the default file commented, and include an overrides file (
postgresql.local.conf). That way, I have an easy reference for what the defaults are, and minimum changes when a new version of postgresql.conf lands (you do know that
checkpoint_segments is obsolete in 9.5, and you can’t specify it, right?). It’s easy for me to see what I’ve changed, since I can just consult that one included file.
I highly recommend this. But whatever you do, don’t do the “some things in the middle, some things at the end,” please. The next person to edit the file will thank you.
11 February 2016
I’ve noticed an increasing tendency in PostgreSQL users to over-index tables, often constructing very complex partial indexes to try to speed up very particular queries.
Be careful about doing this. Not only do additional indexes increase the plan time, they greatly increase insert time.
By way of example, I created a table with a single bigint column, and populated it with:
time psql -c "insert into t select generate_series(1, 100000000)"
That run without any indexes took 1 minute, 55 seconds; that run with eight indexes on the same table took 26 minutes, 39 seconds, or almost 14 times slower.
pg_stat_user_indexes and drop indexes that aren’t being used. Your disk space and insert times will thank you.
9 February 2016
8 February 2016
The slides from my talk at PG Day at FOSDEM 2016 are now available.
2 February 2016
The PostgreSQL statistics collector generates a lot of very important statistics about the state of the database. If it’s not working, autovacuum doesn’t work, among other problems. But it does generate a lot of write activity, and by default, that goes back onto the database volume.
Instead, always set statstempdirectory to point to a RAM disk (which has to be owned by the
postgres user, with 0600 permissions). The statistics are written back to the database on shutdown, so in normal operations, you won’t lose anything on a reboot. (You’ll lose the most recent statistics on a crash, but you will anyway; the statistics are reset on recovery operations, including restart from a crash.)
This can substantially cut down the amount of write I/O the main database storage volume has to receive, and it’s free!
25 January 2016