From: Bill Measday <bill@measday.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Substantial different index use between 9.5 and 9.6
Date: Fri, 2 Dec 2016 11:26:09 +1100
Message-ID: <c04c008a-0a79-7c7b-c09f-8ed3db3b36c5@measday.com> (raw)
In-Reply-To: <21406.1480636092@sss.pgh.pa.us>
References: <c5d43892-7382-5105-67d0-c7800eac77f8@measday.com>
<21406.1480636092@sss.pgh.pa.us>
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Thanks Tom.
First, this wasn't a migration but new db loaded from scratch (if that
matters).
As per the end of the original post "I have vacuum analysed both
tables". I assume this is what you meant?
My gut feel was that it isn't a postgis issue since the third example I
gave uses the index, but I will take it up with them too.
Rgds
Bill
On 2/12/2016 10:48 AM, Tom Lane wrote:
> 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: bill@measday.com, tgl@sss.pgh.pa.us
Subject: Re: Substantial different index use between 9.5 and 9.6
In-Reply-To: <c04c008a-0a79-7c7b-c09f-8ed3db3b36c5@measday.com>
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