On Thu, Aug 01, 2013 at 07:17:27PM +0400, Sergey Burladyan wrote: - Sergey Burladyan <eshkinkot@xxxxxxxxx> writes: - - > # explain - > # select i.item_id, u.user_id from items i - > # left join users u on u.user_id = i.user_id - > # where item_id = 169946840; - > QUERY PLAN - > ---------------------------------------------------------------------------------------------- - > Nested Loop Left Join (cost=0.00..397.14 rows=1 width=16) - > -> Index Scan using items_item_ux on items i (cost=0.00..358.84 rows=1 width=16) - > Index Cond: (item_id = 169946840) - > -> Index Only Scan using users_user_id_pkey on users u (cost=0.00..38.30 rows=1 width=8) - > Index Cond: (user_id = i.user_id) - > - > time: 55919.910 ms - - While running this EXPLAIN backend use disk for a long time: - TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND - 21638 be/4 postgres 2.10 M/s 9.45 M/s 0.00 % 69.04 % postgres: postgres xxxxx xxx.xxx.xxx.xxx(50987) EXPLAIN - - Why it read and write to disk 10 megabytes per second for EXPLAIN query? Cannot understand what is going on here :( That sounds familiar - is it possible you're running into this? http://www.postgresql.org/message-id/20120713065122.GA45804@xxxxxxxxxxxxxx -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
