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Thread: query slowdown after 9.0 -> 9.4 migration

query slowdown after 9.0 -> 9.4 migration

From
Filip Rembiałkowski
Date:
Hi.

Query run time degraded after migration from Pg 9.0 + postgis 1.5 to Pg 9.4 + postgis 2.2.

1 ms versus 7 ms.

Same query, same data, same schema, similar hardware. Data is small and fits in cache.

EXPLAIN shows heap scan cost increase. What can be the reason for 40-fold increase in page scans needed to run Bitmap Heap Scan with Filter and Recheck?

GIST index performance looks OK.


PostgreSQL 9.0.23 on x86_64-suse-linux-gnu, compiled by GCC gcc (SUSE Linux) 4.8.3 20140627 [gcc-4_8-branch revision 212064], 64-bit
POSTGIS="1.5.4" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" LIBXML="2.7.8" USE_STATS (procs from 1.5 r5976 need upgrade)
-> https://explain.depesz.com/s/C3Vw

PostgreSQL 9.4.7 on x86_64-suse-linux-gnu, compiled by gcc (SUSE Linux) 4.8.5, 64-bit
POSTGIS="2.2.2 r14797" GEOS="3.5.0-CAPI-1.9.0 r4084" PROJ="Rel. 4.9.2, 08 September 2015" GDAL="GDAL 2.1.0, released 2016/04/25 GDAL_DATA not found" LIBXML="2.9.1" LIBJSON="0.12" (core procs from "2.2.1 r14555" need upgrade) TOPOLOGY (topology procs from "2.2.1 r14555" need upgrade) RASTER (raster procs from "2.2.1 r14555" need upgrade)
-> https://explain.depesz.com/s/24GA


Query:

SELECT round(meters_to_miles(st_distance_sphere(ST_GeomFromText('POINT(-77.0364 38.89524)', 4326),llpoint))::numeric,2) as _distance FROM storelocator WHERE st_expand(ST_GeomFromText('POINT(-77.0364 38.89524)', 4326), miles_to_degree(50,38.89524)) && llpoint AND st_distance_sphere(ST_GeomFromText('POINT(-77.0364 38.89524)', 4326), llpoint) <= miles_to_meters(50) ORDER BY _distance LIMIT 10;



thanks for any suggestions / ideas.



Filip


Re: query slowdown after 9.0 -> 9.4 migration

From
Tomas Vondra
Date:
On 10/26/2016 03:48 PM, Filip Rembiałkowski wrote:
> Hi.
>
> Query run time degraded after migration from Pg 9.0 + postgis 1.5 to Pg
> 9.4 + postgis 2.2.
>
> 1 ms versus 7 ms.
>
> Same query, same data, same schema, similar hardware. Data is small and
> fits in cache.
>
> EXPLAIN shows heap scan cost increase. What can be the reason for
> 40-fold increase in page scans needed to run Bitmap Heap Scan with
> Filter and Recheck?
>

On 9.0 the the scan accesses only 8 buffers:

Buffers: shared hit=8

while on 9.4 it has to inspect 316 of them:

Buffers: shared hit=316

Perhaps the table is organized / sorted differently, or something like
that. How did you do the upgrade?


ragards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Re: query slowdown after 9.0 -> 9.4 migration

From
Andreas Kretschmer
Date:
Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:

> On 10/26/2016 03:48 PM, Filip Rembiałkowski wrote:
>> Hi.
>>
>> Query run time degraded after migration from Pg 9.0 + postgis 1.5 to Pg
>> 9.4 + postgis 2.2.
>> EXPLAIN shows heap scan cost increase. What can be the reason for
>> 40-fold increase in page scans needed to run Bitmap Heap Scan with
>> Filter and Recheck?
>>
>
> On 9.0 the the scan accesses only 8 buffers:
>
> Buffers: shared hit=8
>
> while on 9.4 it has to inspect 316 of them:
>
> Buffers: shared hit=316

nice point ;-)


>
> Perhaps the table is organized / sorted differently, or something like
> that. How did you do the upgrade?

Maybe table-bloat? Filip, check if autovacuum runs properly.



Regards, Andreas Kretschmer
--
Andreas Kretschmer
http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Re: query slowdown after 9.0 -> 9.4 migration

From
Filip Rembiałkowski
Date:

On Thu, Oct 27, 2016 at 7:38 AM, Andreas Kretschmer <akretschmer@spamfence.net> wrote:
Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:

>
> Perhaps the table is organized / sorted differently, or something like
> that. How did you do the upgrade?


Nothing special, dump + reload. The table in question is tiny - 280 kB, 859 rows.

 
Maybe table-bloat? Filip, check if autovacuum runs properly.

​
Yes, it does. Just to be sure I ran VACUUM FULL, ANALZYE and REINDEX on all tables and indexes - no change :-(

Any other ideas (before drawing on heavy tools like strace)?


Does it make sense to ask on postgis-users list?

​

​Thanks,
Filip
​

Re: query slowdown after 9.0 -> 9.4 migration

From
Jim Nasby
Date:
On 10/27/16 8:37 PM, Filip Rembiałkowski wrote:
> Does it make sense to ask on postgis-users list?

Yes. I suspect that the reason Buffers: shared hit is so high is because
of something st_distance_sphere() is doing.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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