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 :( -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
