From: | Bill Measday <bill(at)measday(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Substantial different index use between 9.5 and 9.6 |
Date: | 2016-12-02 00:26:09 |
Message-ID: | c04c008a-0a79-7c7b-c09f-8ed3db3b36c5@measday.com |
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Lists: | pgsql-performance |
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(at)measday(dot)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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