Re: query plan question, nested loop vs hash join

2014-10-05 21:57 GMT+03:00 Andrey Lizenko <lizenko79@gmail.com>:

Increasing  of 'effective_cache_size' leads to similar thing with mergejoin, 

other options (work_mem, shared_buffers. etc) do not change anything.

I think increasing `work_mem` should have effects, as plan with `Nested Loop` is using disk-based sort.

Increase it till you'll stop seeing `external sort` in the EXPLAIN output. Something like '10MB' should do.

Also, it'd be handy if you could provide `EXPLAIN (analyze, buffers)` output along with the results of these queries:

    SELECT name,setting,source FROM pg_settings WHERE name ~ 'cost' AND NOT name ~ 'vacuum';

    SELECT name,setting,source FROM pg_settings WHERE NOT source IN ('default','override');

And describe your setup: what OS? how much RAM? what kind of disks? RAID?

--
Victor Y. Yegorov