Hello,
I'm running this PostGIS Raster query
select
st_scalex(rast),
st_scaley(rast),
st_skewx(rast),
st_skewy(rast),
st_width(rast),
st_height(rast),
rid,
st_upperleftx(rast),
st_upperlefty(rast),
st_numbands(rast)
from
my_postgis_raster_table
I want to remark that, even when 'rast' is a complex type and can be really
big, I'm getting just metadata. Not the whole 'rast' column. Anyway, the
average dimensions of a 'rast' column in like 600x400 pixels (8 bits per
pixel). So, not so big (about 234 KB per rast object).
My table has 1257 rows, and this query takes about 45 secs to execute (45646
msecs). I think it's too slow. I'm just getting metadata, not the whole 'rast'
object, as said.
This is the explain analyze output
Seq Scan on my_postgis_raster_table (cost=0.00..198.85 rows=1257 width=36)
(actual time=86.867..51861.495 rows=1257 loops=1)
Total runtime: 51863.919 ms
So, basically a sequential scan. As expected, I guess (I'm not a postgres
expert, so sorry if I'm talking nonsense)
I've calculated the effective transfer rate for this table
SELECT pg_size_pretty(CAST(pg_relation_size('my_postgis_raster_table') / 45646
* 1000 as int8)) AS bytes_per_second;
As it's 27KB. Isn't it a slow rate? Is there any kind of index I could create
to speed this query? Maybe use some kind of cache system?
Many thanks in advance,
--
Jorge Arevalo
Freelance developer
http://www.krop.com/jorgearevalo
http://about.me/jorgeas80
Enviado con Sparrow (http://www.sparrowmailapp.com/?sig)
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