[postgis-users] On UpdateGeometrySRID() performance

[Paul Ramsey]

Also, if you created an index during your import process, that'll also make
your update slower.
I usually skip bulk updates in favour of writing a fresh table with the
stuff I want..

CREATE TABLE mynewtable AS SELECT ST_SetSRID(geom, 4326) AS geom, ... FROM
myoldtable

That generally writes as fast as is possible though still only single
threaded.

P


On Thu, Nov 1, 2018 at 9:51 AM Darafei "Komяpa" Praliaskouski <me at komzpa.net>
wrote:

> Hi,
>
> Please feed in your WKT polygons in EWKT format:
>
> SRID=4326;POLYGON(...)
>
> Since every update in Postgres is essentially Delete+Insert, time of
> rewriting each and every row being equal to initial Insert time is expected
> thing.
>
> You can also update SRID in two columns in one go:
>
> update tablename set geom1 = ST_SetSRID(geom1, 4326), geom2 =
> ST_SetSRID(geom2, 4326);
>
> Out of curiosity, where did you learn about UpdateGeometrySRID before
> learning about ST_SetSRID?
>
> ср, 31 окт. 2018 г. в 21:57, jerry73204 <jerry73204 at gmail.com>:
>
>> Hi all,
>>
>> I'm stuck in the low performance of UpdateGeometrySRID().
>>
>> I get started with a 50GB polygon dataset in CSV in EPSG:4326
>> coordinates. Since I find no way to `\copy` the csv while preserving the
>> SRID, the data is imported with null SRID and then `SELECT
>> UpdateGeometrySRID('table', 'column', 4326)`.
>>
>> The `UpdateGeometrySRID()` takes as long time as that of `\copy`, which
>> turns out to be approx two hours. The dataset has two geometry columns
>> and thus I have to take triple time to finish this data.
>>
>> I profiled the postgresql daemon. The avg disk writing speed is 30MB/s,
>> while occasionally peaks to 100MB/s. The SSD, F2FS formatted disk is
>> capable of up to 150MB/s. The daemon does not utilize the 4-core
>> i5-7600k CPU. It seems to be a single process task with avg CPU load
>> 20%, while other workers are idle. I wonder if there's a room for
>> improving the performance. Also, I'm looking for if it's possible to
>> preserve SRID with `\copy`.
>>
>> Jerry Lin
>>
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>
> --
> Darafei Praliaskouski
> Support me: http://patreon.com/komzpa
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