Re: RFD: Discarded tuple count for SeqScan nodes in EXPLAIN ANALYZE

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: RFD: Discarded tuple count for SeqScan nodes in EXPLAIN ANALYZE
Date: 2009-05-22 15:54:21
Message-ID: 26176.1243007661@sss.pgh.pa.us
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On 05/22/2009 03:42 PM, Heikki Linnakangas wrote:
>> Isn't the discarded count always equal to (# of rows in table - matched
>> tuples)? Seems pretty redundant to me.

> Not for EXISTS(), LIMIT and similar.

It doesn't really seem useful enough to justify breaking client-side
code that looks at EXPLAIN output.

This sort of ties into the discussions we have periodically about
allowing EXPLAIN to output XML or some other more-machine-friendly
data format. The barrier for adding additional output fields would
be a lot lower in such a format.

regards, tom lane

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