Re: large tables and simple "= constant" queries using indexes

On Thu, 10 Apr 2008, PFC wrote:

... Lots of useful advice ...

> - If you often query rows with the same gene_ref, consider using
> CLUSTER to physically group those rows on disk. This way you can get all rows
> with the same gene_ref in 1 seek instead of 2000. Clustered tables also make
> Bitmap scan happy.

In my opinion this is the one that will make the most difference. You will
need to run:

CLUSTER gene_prediction_view USING gene_prediction_view_gene_ref_key;

after you insert significant amounts of data into the table. This
re-orders the table according to the index, but new data is always written
out of order, so after adding lots more data the table will need to be
re-clustered again.

> - Switch to a RAID10 (4 times the IOs per second, however zero gain if
> you're single-threaded, but massive gain when concurrent)

Greg Stark has a patch in the pipeline that will change this, for bitmap
index scans, by using fadvise(), so a single thread can utilise multiple
discs in a RAID array.

Matthew

--
Prolog doesn't have enough parentheses. -- Computer Science Lecturer