Try running that query directly against the database see how long that
takes.
Also try running explain on that query make sure it is using your
indexes properly.
Since you are only using a single filter make sure that the
spectrum_header.filename
has an index, and make sure your foreign key column
spectrum.spectrum_header_pk
is indexed as well.
On 07/19/2010 08:46 AM, Adrian Price-Whelan wrote:
does it take a few seconds to fully fetch all the results and it only gets 1000
rows ? or is that just to get the initial result?
I'm not sure what you mean by this - the query does return 1000 rows.
also if any of the individual columns are very large BLOBs or perhaps very
large PG arrays that would add to the overhead of a fetch.
There definitely are columns of PG arrays ~4000 elements each, so back
to my first email it seems like the culprit here could be the ARRAY's
Thanks for your help,
Adrian
On Jul 19, 10:10 am, Michael Bayer<mike...@zzzcomputing.com> wrote:
On Jul 19, 2010, at 9:52 AM, Adrian Price-Whelan wrote:
Hi,
I was just wondering at first whether there was a known issue with
ARRAY types, but here is the query:
spectra =
session.query(Spectrum).join(SpectrumHeader).filter(SpectrumHeader.filename
== spPlateFilename).all()
It should return ~1000 objects equaling about 120MB of data. In
Python, this query takes>10 minutes to complete, but as a SQL query
(copying and pasting the echo'd command) it takes a few seconds:
SELECT spectrum.pk AS spectrum_pk, spectrum.ra AS spectrum_ra,
spectrum.dec AS spectrum_dec, spectrum.values AS spectrum_values,
spectrum.spectrum_header_pk AS spectrum_spectrum_header_pk,
spectrum.fiber_number AS spectrum_fiber_number, spectrum.inv_var AS
spectrum_inv_var, spectrum.and_mask AS spectrum_and_mask,
spectrum.or_mask AS spectrum_or_mask FROM spectrum JOIN
spectrum_header ON spectrum_header.pk = spectrum.spectrum_header_pk
WHERE spectrum_header.filename = 'spPlate-3586-55181.fits'
autoflush and autocommit are both set to False.
It seems like a straightforward query so I'm confused as to what could
be getting hung up.
does it take a few seconds to fully fetch all the results and it only gets 1000
rows ? or is that just to get the initial result? these are different things.
also if any of the individual columns are very large BLOBs or perhaps very
large PG arrays that would add to the overhead of a fetch. You can also try
writing a DBAPI-only script that runs the query, as well as running
engine.execute(myquery.statement) and fetching rows that way to see if some
in-object process is the factor (which is unlikely).
Thanks for any insight,
Adrian
On Jul 16, 10:24 pm, Michael Bayer<mike...@zzzcomputing.com> wrote:
You absolutely need to turn in echoing and locate the specific SQL query which
causes the issue. Queries can take excessive time for a very wide variety of
reasons.
On Jul 16, 2010, at 12:56 PM, Adrian Price-Whelan wrote:
Hello --
I'm working with a database populated with data originally from a file
structure of files that are ~150MB each. We are dealing with a lot of data that
is being stored in the database using the 'ARRAY' datatype, specifically
numeric[]. After loading some of the data into the database I tried performing
a query to get back some data, and comparing it with code that reads directly
from the file system - but the database query took ~50 times longer to
complete. For instance, to retrieve 100 records that contain a few 4000 element
arrays each using the code that reads the filesystem it took less than a
second, but the query on the database took around 25 seconds to complete. Has
anyone else had issues with array types slowing down queries or does this sound
more like another issue?
Thanks!
Adrian
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