From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bill Measday <bill@measday.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Substantial different index use between 9.5 and 9.6
Date: Thu, 01 Dec 2016 18:48:12 -0500
Message-ID: <21406.1480636092@sss.pgh.pa.us> (raw)
In-Reply-To: <c5d43892-7382-5105-67d0-c7800eac77f8@measday.com>
References: <c5d43892-7382-5105-67d0-c7800eac77f8@measday.com>
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Bill Measday <bill@measday.com> writes:
> Substantial different index use between 9.5 and 9.6
Maybe you missed an ANALYZE after migrating? The plan difference
seems to be due to a vast difference in rowcount estimate for the
m_elevations condition:
> -> Bitmap Heap Scan on m_elevations e
> (cost=282802.21..37401439.43 rows=3512160 width=8)
> -> Seq Scan on m_elevations e
> (cost=10000000000.00..13296950520.12 rows=3512159563 width=8)
If you don't know where that factor-of-1000 came from, maybe take
it up with the postgis folk. It'd mostly be coming out of their
selectivity estimation routines.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, bill@measday.com
Subject: Re: Substantial different index use between 9.5 and 9.6
In-Reply-To: <21406.1480636092@sss.pgh.pa.us>
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