[postgis-users] On UpdateGeometrySRID() performance
jerry73204
jerry73204 at gmail.com
Thu Nov 1 10:03:17 PDT 2018
Thanks for your reply.
I missed EWKT trick so much. `sed` before copy may save more time.
To Darafei's question: I simply google://"postgis change srid" to find
out UpdateGeometrySRID.
Jerry Lin
On 11/2/18 12:51 AM, Darafei "Komяpa" Praliaskouski 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
> <mailto: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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