From: Sergey Burladyan <eshkinkot@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Looks like merge join planning time is too big, 55 seconds
Date: Thu, 01 Aug 2013 19:17:27 +0400
Message-ID: <8761vpwid4.fsf@seb.koffice.internal> (raw)
In-Reply-To: <CAJ2ymdjK-+LZHFY+cskRq98c_4F1PEfveOVNbNGpWL0Pczy5Ew@mail.gmail.com>
References: <CAJ2ymdjK-+LZHFY+cskRq98c_4F1PEfveOVNbNGpWL0Pczy5Ew@mail.gmail.com>
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Sergey Burladyan <eshkinkot@gmail.com> 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 :(
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To: pgsql-performance@postgresql.org
Cc: eshkinkot@gmail.com
Subject: Re: Looks like merge join planning time is too big, 55 seconds
In-Reply-To: <8761vpwid4.fsf@seb.koffice.internal>
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