From: mallah@trade-india.com
To: josh@agliodbs.com
Cc: mallah@trade-india.com
Cc: pgsql-sql@postgresql.org
Subject: Re: Why is seq search preferred here by planner?
Date: Thu, 24 Apr 2003 01:43:29 +0530 (IST)
Message-ID: <1386.219.65.253.85.1051128809.squirrel@mail.trade-india.com> (raw)
In-Reply-To: <200304231253.52051.josh@agliodbs.com>
References: <1220.219.65.235.51.1051114881.squirrel@mail.trade-india.com>
<200304231120.56699.josh@agliodbs.com>
<1331.219.65.233.8.1051123905.squirrel@mail.trade-india.com>
<200304231253.52051.josh@agliodbs.com>
> Mallah,
>
>> > The reason that the planner is using a seq scan on
> personal_account_details is the same as the
>> > reason for using a seq scan on email_bank; the number of rows which
> match the condition,
>> > about 150,000. With that many qualifying rows, a seq scan is faster.
>>
>>
>> But there are two tables here , email_bank and personal_account_details in personal account
>> details only one row is supposed to match a given userid as userid is the PKEY , why seq_scan
>> there ? or am i getting the explain
> wrong ?
>
> It doesn't matter whether it's a primary key or not. If your query or subquery condition
> returns a large number/proportion of rows, a seq scan is going to be faster than an index
> scan.
>
> As far as userid being a key, this affects the planner's *join method*, *not* how the database
> gets the rows.
Got it , you mean to say userid being pkey is affecting the method of
implicit join being made by the update stmt.
thanks once again.
Regds
mallah.
>
>
> --
> -Josh Berkus
> Aglio Database Solutions
> San Francisco
-----------------------------------------
Get your free web based email at trade-india.com.
"India's Leading B2B eMarketplace.!"
http://www.trade-india.com/
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: mallah@trade-india.com, josh@agliodbs.com
Subject: Re: Why is seq search preferred here by planner?
In-Reply-To: <1386.219.65.253.85.1051128809.squirrel@mail.trade-india.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox