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Am 23.11.2006 um 23:37 schrieb Gopal:
> hared_buffers = 20000 # min 16 or
> max_connections*2, 8KB each
If this is not a copy & paste error, you should add the "s" at the
beginning of the line.

Also you might want to set this to a higher number. You are setting
about 20000 * 8k = 160MB, this number might be a bit too small if you
do a lot of queries spread over the whole dataset. I don't know
whether the memory management on Windows handles this well, but you
can give it a try.
> effective_cache_size = 82728 # typically 8KB each
Hmm. I don't know what the real effect of this might be as the doc
states:

"This parameter has no effect on the size of shared memory allocated
by PostgreSQL, nor does it reserve kernel disk cache; it is used only
for estimation purposes."

You should try optimizing your shared_buffers to cache more of the data.
> But postgres has everything spread across 10-15 processes, with
> each process using about 10-30MB, not nearly enough to cache all
> the data and ends up doing a lot of disk reads.
It's not soo easy. PostgreSQL maintains a shared_buffer which is
accessible by all processes for reading. On a Unix system you can see
this in the output of top - don't know how this works on Windows.
> In any case I cannot believe that having 15-20 processes running on
> windows helps. Why not spwan of threads instead of processes, which
> migh be far less expensive and more efficient. Is there any way of
> doing this?
Because it brings you a whole lot of other problems? And because
PostgreSQL is not "made for Windows". PostgreSQL runs very good on
Linux, BSD, Mac OS X and others. The Windows version is quite young.

But before you blame stuff on PostgreSQL you should give more
information about the query itself.
> My question is, should I just accept the performance I am getting
> as the limit on windows or should I be looking at some other params
> that I might have missed?
Post the "explain analyse select <your query here>" output here. That
might help to understand, why you get such a high CPU load.

cug

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On Fri, 24 Nov 2006 09:22:45 +0100
Guido Neitzer <lists@event-s.net> wrote:

> > effective_cache_size = 82728 # typically 8KB each
> Hmm. I don't know what the real effect of this might be as the doc
> states:
>
> "This parameter has no effect on the size of shared memory allocated
> by PostgreSQL, nor does it reserve kernel disk cache; it is used
> only for estimation purposes."

This is a hint to the optimizer about how much of the database may
be in the OS level cache.

---------------------------------
Frank Wiles <frank@wiles.org>
http://www.wiles.org
---------------------------------


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Tom,

This is the query and the schema....

Query is :
SELECT subq.percentCover, ds.datasetname, ds.maxresolution
FROM
(
select
sum(area(intersection(snaptogrid(chunkgeometry,0.0 0000001),
GeometryFromText('POLYGON((-0.140030845589332
50.8208343077265,-0.138958398039148 50.8478005422809,-0.0963639712296823
50.8471133071392,-0.0974609286275892 50.8201477285483,-0.140030845589332
50.8208343077265))',4326))) * 100/ (0.00114901195862628)) as
percentCover,
datasetid as did from
tbl_metadata_chunks
where chunkgeometry &&
GeometryFromText('POLYGON((-0.140030845589332
50.8208343077265,-0.138958398039148 50.8478005422809,-0.0963639712296823
50.8471133071392,-0.0974609286275892 50.8201477285483,-0.140030845589332
50.8208343077265))',4326)
and datasetid in (select datasetid from
tbl_metadata_dataset where typeofdataid=1)
group by did
order by did desc
)
AS subq INNER JOIN tbl_metadata_dataset AS
ds ON subq.did = ds.datasetid
ORDER by ceil(subq.percentCover),1/ds.maxresolution
DESC;


Schema is

Table 1
CREATE TABLE public.tbl_metadata_dataset
(
datasetname varchar(70) NOT NULL,
maxresolution real,
typeofdataid integer NOT NULL,
datasetid serial NOT NULL,
CONSTRAINT "PK_Dataset" PRIMARY KEY (datasetid)
);
-- Indexes
CREATE INDEX dsnameindex ON tbl_metadata_dataset USING btree
(datasetname);-- Owner
ALTER TABLE public.tbl_metadata_dataset OWNER TO postgres;
-- Triggers
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2196039" AFTER DELETE ON
tbl_metadata_dataset FROM tbl_metadata_chunks NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_noaction_del"('dsid',
'tbl_metadata_chunks', 'tbl_metadata_dataset', 'UNSPECIFIED',
'datasetid', 'datasetid');
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2196040" AFTER UPDATE ON
tbl_metadata_dataset FROM tbl_metadata_chunks NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_noaction_upd"('dsid',
'tbl_metadata_chunks', 'tbl_metadata_dataset', 'UNSPECIFIED',
'datasetid', 'datasetid');


Table 2

CREATE TABLE public.tbl_metadata_chunks
(
chunkid serial NOT NULL,
chunkgeometry geometry NOT NULL,
datasetid integer NOT NULL,
CONSTRAINT tbl_metadata_chunks_pkey PRIMARY KEY (chunkid),
CONSTRAINT dsid FOREIGN KEY (datasetid) REFERENCES
tbl_metadata_dataset(datasetid)
);
-- Indexes
CREATE INDEX idx_dsid ON tbl_metadata_chunks USING btree (datasetid);
CREATE UNIQUE INDEX tbl_metadata_chunks_idx2 ON tbl_metadata_chunks
USING btree (nativetlx, nativetly, datasetid);
CREATE INDEX tbl_metadata_chunks_idx3 ON tbl_metadata_chunks USING gist
(chunkgeometry);-- Owner
ALTER TABLE public.tbl_metadata_chunks OWNER TO postgres;
-- Triggers
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2194515" AFTER DELETE ON
tbl_metadata_chunks FROM tbl_metadata_chunkinfo NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_restrict_del"('fk',
'tbl_metadata_chunkinfo', 'tbl_metadata_chunks', 'UNSPECIFIED',
'chunkid', 'chunkid');
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2194516" AFTER UPDATE ON
tbl_metadata_chunks FROM tbl_metadata_chunkinfo NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_restrict_upd"('fk',
'tbl_metadata_chunkinfo', 'tbl_metadata_chunks', 'UNSPECIFIED',
'chunkid', 'chunkid');
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2196037" AFTER INSERT ON
tbl_metadata_chunks FROM tbl_metadata_dataset NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_check_ins"('dsid',
'tbl_metadata_chunks', 'tbl_metadata_dataset', 'UNSPECIFIED',
'datasetid', 'datasetid');
CREATE CONSTRAINT TRIGGER "RI_ConstraintTrigger_2196038" AFTER UPDATE ON
tbl_metadata_chunks FROM tbl_metadata_dataset NOT DEFERRABLE INITIALLY
IMMEDIATE FOR EACH ROW EXECUTE PROCEDURE "RI_FKey_check_upd"('dsid',
'tbl_metadata_chunks', 'tbl_metadata_dataset', 'UNSPECIFIED',
'datasetid', 'datasetid');



-----Original Message-----
From: Frank Wiles [mailto:frank@wiles.org]
Sent: 24 November 2006 17:05
To: Guido Neitzer
Cc: Gopal; pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Postgres scalability and performance on windows

On Fri, 24 Nov 2006 09:22:45 +0100
Guido Neitzer <lists@event-s.net> wrote:

> > effective_cache_size = 82728 # typically 8KB each
> Hmm. I don't know what the real effect of this might be as the doc
> states:
>
> "This parameter has no effect on the size of shared memory allocated
> by PostgreSQL, nor does it reserve kernel disk cache; it is used
> only for estimation purposes."

This is a hint to the optimizer about how much of the database may
be in the OS level cache.

---------------------------------
Frank Wiles <frank@wiles.org>
http://www.wiles.org
---------------------------------


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"Gopal" <gopal@getmapping.com> writes:
> This is the query and the schema....
> ...
> select
> sum(area(intersection(snaptogrid(chunkgeometry,0.0 0000001),
> GeometryFromText('POLYGON((-0.140030845589332
> 50.8208343077265,-0.138958398039148 50.8478005422809,-0.0963639712296823
> 50.8471133071392,-0.0974609286275892 50.8201477285483,-0.140030845589332
> 50.8208343077265))',4326))) * 100/ (0.00114901195862628)) as
> percentCover,

So evidently area(intersection(snaptogrid(...))) takes about 300
microsec per row. The PostGIS hackers would have to comment on whether
that seems out-of-line or not, and whether you can make it faster.

regards, tom lane

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On Nov 28, 2006, at 8:24 AM, Tom Lane wrote:
> "Gopal" <gopal@getmapping.com> writes:
>> This is the query and the schema....
>> ...
>> select
>> sum(area(intersection(snaptogrid(chunkgeometry,0.0 0000001),
>> GeometryFromText('POLYGON((-0.140030845589332
>> 50.8208343077265,-0.138958398039148
>> 50.8478005422809,-0.0963639712296823
>> 50.8471133071392,-0.0974609286275892
>> 50.8201477285483,-0.140030845589332
>> 50.8208343077265))',4326))) * 100/ (0.00114901195862628)) as
>> percentCover,
>
> So evidently area(intersection(snaptogrid(...))) takes about 300
> microsec per row. The PostGIS hackers would have to comment on
> whether
> that seems out-of-line or not, and whether you can make it faster.


This is consistent with the typical cost for GIS geometry ops -- they
are relatively expensive. When running queries against PostGIS
fields for our apps, about half the CPU time will be spent inside the
geometry ops. Fortunately, there is significant opportunity for
improvement in the performance of the underlying code if anyone found
the time to optimize (and uglify) it for raw speed.


Cheers,

J. Andrew Rogers


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