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Date: Mon, 6 Mar 2017 09:46:32 -0700 (MST)
From: twoflower <standa.kurik@gmail.com>
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Subject: Re: Huge difference between ASC and DESC ordering
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Thank you Jeff.

There are 7 million rows satisfying fk_id_client = 20045. There is an index
on fk_id_client, now I added a composite (fk_id_client, id) index but that
did not help.

I see the point of what you are saying, but still don't understand how these
two situations (*asc* vs. *desc*) are not symmetrical. I mean, there /is/ an
ascending index on *JOB_MEMORY.id*, so why does it matter which end I am
picking the data from?

The thing is, even when I force Postgres to use the ascending index on *id*,
it's still orders of magnitude slower than the *desc* version (even when
that one goes through the index backwards).



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Thank you Jeff.
<br /><br />
There are 7 million rows satisfying fk_id_client = 20045. There is an index on fk_id_client, now I added a composite (fk_id_client, id) index but that did not help.
<br /><br />
I see the point of what you are saying, but still don't understand how these two situations (<b>asc</b> vs. <b>desc</b>) are not symmetrical. I mean, there <i>is</i> an ascending index on <b>JOB_MEMORY.id</b>, so why does it matter which end I am picking the data from?
<br /><br />
The thing is, even when I force Postgres to use the ascending index on <b>id</b>, it's still orders of magnitude slower than the <b>desc</b> version (even when that one goes through the index backwards).






	
	
	
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View this message in context: <a href="http://www.postgresql-archive.org/Huge-difference-between-ASC-and-DESC-ordering-tp5947712p5947737.html">Re: Huge difference between ASC and DESC ordering</a><br/>
Sent from the <a href="http://www.postgresql-archive.org/PostgreSQL-performance-f2050081.html">PostgreSQL - performance mailing list archive</a> at Nabble.com.<br/>
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