Re: [PERFORM] Possible to improve query plan?
2011/1/25 Kevin Grittner kevin.gritt...@wicourts.gov: Jeremy Palmer jpal...@linz.govt.nz wrote: Kevin I've now clustered the table. And the performance did increase quite a bit. Yeah, that's enough to notice the difference. My only question is how often will I need to re-cluster the table, because it comes at quite a cost. The setup I'm running will mean that 10,000 new rows will be inserted, and 2,500 rows will be updated on this table each day. You're going to see performance drop off as the data fragments. You'll need to balance the performance against maintenance down-time. I would guess, though, that if you have a weekly maintenance window big enough to handle the CLUSTER, it might be worth doing it that often. Was FILLFACTOR already suggested regarding the INSERT vs UPDATE per day ? http://www.postgresql.org/docs/9.0/static/sql-altertable.html (and index too, but they already have a default at 90% for btree) -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Cédric Villemain 2ndQuadrant http://2ndQuadrant.fr/ PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
On Mon, Jan 17, 2011 at 11:48 AM, Kevin Grittner kevin.gritt...@wicourts.gov wrote: Jeremy Palmer wrote: WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40)) - Bitmap Heap Scan on version_crs_coordinate_revision (actual time=70.925..13531.720 rows=149557 loops=1) - BitmapOr (actual time=53.650..53.650 rows=0 loops=1) This plan actually looks pretty good for what you're doing. The Bitmap Index Scans and BitmapOr determine which tuples in the heap need to be visited. The Bitmap Heap Scan then visits the heap pages in physical order (to avoid repeated fetches of the same page and to possibly edge toward sequential access speeds). You don't seem to have a lot of bloat, which could be a killer on this type of query, since the rowcounts from the index scans aren't that much higher than the counts after you check the heap. But isn't 13.5 seconds awfully slow to scan 149557 rows? The sort is sorting 23960kB. Dividing that by 149557 rows gives ~169 bytes/per row, or roughly 49 rows per block, which works out to 3k blows, or about 24MB of data. Clearly we must be hitting a LOT more data than that, or this would be much faster than it is, I would think. Any chance this is 9.0.X? It'd be interesting to see the EXPLAIN (ANALYZE, BUFFERS) output for this query. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Robert Haas robertmh...@gmail.com wrote: But isn't 13.5 seconds awfully slow to scan 149557 rows? The sort is sorting 23960kB. Dividing that by 149557 rows gives ~169 bytes/per row You're right. I would expect 9 ms as per tuple as a worst case if it doesn't need to go to TOAST data. Caching, multiple rows per page, or adjacent pages should all tend to bring it down from there. How does it get to 90 ms per row with rows that narrow? Is the table perhaps horribly bloated? Jeremy, did you try my suggestion of using CLUSTER on the index which will tend to be more selective? -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Robert Haas robertmh...@gmail.com writes: But isn't 13.5 seconds awfully slow to scan 149557 rows? Depends on how many physical blocks they're scattered across, which is hard to tell from this printout. And on how many of the blocks are already in cache, and what sort of disk hardware he's got, etc. Any chance this is 9.0.X? It'd be interesting to see the EXPLAIN (ANALYZE, BUFFERS) output for this query. Yeah. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Kevin Grittner kevin.gritt...@wicourts.gov writes: Robert Haas robertmh...@gmail.com wrote: But isn't 13.5 seconds awfully slow to scan 149557 rows? The sort is sorting 23960kB. Dividing that by 149557 rows gives ~169 bytes/per row You're right. I would expect 9 ms as per tuple as a worst case if it doesn't need to go to TOAST data. Caching, multiple rows per page, or adjacent pages should all tend to bring it down from there. How does it get to 90 ms per row with rows that narrow? Um, that looks like 90 usec per row, not msec. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Tom Lane t...@sss.pgh.pa.us wrote: Um, that looks like 90 usec per row, not msec. Oh, right. Well, having to do a random heap access for 1% of the rows would pretty much explain the run time, then. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Might be a chance on 9.0 in a couple of weeks, when I do an upgrade on one our dev boxes. Kevin I've now clustered the table. And the performance did increase quite a bit. My only question is how often will I need to re-cluster the table, because it comes at quite a cost. The setup I'm running will mean that 10,000 new rows will be inserted, and 2,500 rows will be updated on this table each day. Here is the new explain output once I have clustered on the idx_crs_coordinate_revision_created index: Subquery Scan t (cost=168227.04..173053.88 rows=743 width=205) (actual time=392.586..946.879 rows=106299 loops=1) Output: t.row_number, t._revision_created, t._revision_expired, t.id, t.cos_id, t.nod_id, t.ort_type_1, t.ort_type_2, t.ort_type_3, t.status, t.sdc_status, t.source, t.value1, t.value2, t.value3, t.wrk_id_created, t.cor_id, t.audit_id Filter: (t.row_number = 1) - WindowAgg (cost=168227.04..171197.40 rows=148518 width=86) (actual time=392.577..834.477 rows=149557 loops=1) Output: row_number() OVER (?), table_version_crs_coordinate_revision._revision_created, table_version_crs_coordinate_revision._revision_expired, table_version_crs_coordinate_revision.id, table_version_crs_coordinate_revision.cos_id, table_version_crs_coordinate_revision.nod_id, table_version_crs_coordinate_revision.ort_type_1, table_version_crs_coordinate_revision.ort_type_2, table_version_crs_coordinate_revision.ort_type_3, table_version_crs_coordinate_revision.status, table_version_crs_coordinate_revision.sdc_status, table_version_crs_coordinate_revision.source, table_version_crs_coordinate_revision.value1, table_version_crs_coordinate_revision.value2, table_version_crs_coordinate_revision.value3, table_version_crs_coordinate_revision.wrk_id_created, table_version_crs_coordinate_revision.cor_id, table_version_crs_coordinate_revision.audit_id - Sort (cost=168227.04..168598.34 rows=148518 width=86) (actual time=392.550..457.460 rows=149557 loops=1) Output: table_version_crs_coordinate_revision._revision_created, table_version_crs_coordinate_revision._revision_expired, table_version_crs_coordinate_revision.id, table_version_crs_coordinate_revision.cos_id, table_version_crs_coordinate_revision.nod_id, table_version_crs_coordinate_revision.ort_type_1, table_version_crs_coordinate_revision.ort_type_2, table_version_crs_coordinate_revision.ort_type_3, table_version_crs_coordinate_revision.status, table_version_crs_coordinate_revision.sdc_status, table_version_crs_coordinate_revision.source, table_version_crs_coordinate_revision.value1, table_version_crs_coordinate_revision.value2, table_version_crs_coordinate_revision.value3, table_version_crs_coordinate_revision.wrk_id_created, table_version_crs_coordinate_revision.cor_id, table_version_crs_coordinate_revision.audit_id Sort Key: table_version_crs_coordinate_revision.id, table_version_crs_coordinate_revision._revision_created Sort Method: quicksort Memory: 23960kB - Bitmap Heap Scan on table_version_crs_coordinate_revision (cost=3215.29..155469.14 rows=148518 width=86) (actual time=38.808..196.993 rows=149557 loops=1) Output: table_version_crs_coordinate_revision._revision_created, table_version_crs_coordinate_revision._revision_expired, table_version_crs_coordinate_revision.id, table_version_crs_coordinate_revision.cos_id, table_version_crs_coordinate_revision.nod_id, table_version_crs_coordinate_revision.ort_type_1, table_version_crs_coordinate_revision.ort_type_2, table_version_crs_coordinate_revision.ort_type_3, table_version_crs_coordinate_revision.status, table_version_crs_coordinate_revision.sdc_status, table_version_crs_coordinate_revision.source, table_version_crs_coordinate_revision.value1, table_version_crs_coordinate_revision.value2, table_version_crs_coordinate_revision.value3, table_version_crs_coordinate_revision.wrk_id_created, table_version_crs_coordinate_revision.cor_id, table_version_crs_coordinate_revision.audit_id Recheck Cond: (((_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) Filter: (((_revision_created = 16) AND (_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) - BitmapOr (cost=3215.29..3215.29 rows=149432 width=0) (actual time=27.330..27.330 rows=0 loops=1) - Bitmap Index Scan on idx_crs_coordinate_revision_expired (cost=0.00..2225.36 rows=106001 width=0) (actual time=21.596..21.596 rows=110326 loops=1) Index Cond: ((_revision_expired 16) AND (_revision_expired = 40)) - Bitmap Index Scan on idx_crs_coordinate_revision_created (cost=0.00..915.67 rows=43432 width=0) (actual time=5.728..5.728 rows=43258 loops=1)
Re: [PERFORM] Possible to improve query plan?
Jeremy Palmer jpal...@linz.govt.nz wrote: Kevin I've now clustered the table. And the performance did increase quite a bit. Yeah, that's enough to notice the difference. My only question is how often will I need to re-cluster the table, because it comes at quite a cost. The setup I'm running will mean that 10,000 new rows will be inserted, and 2,500 rows will be updated on this table each day. You're going to see performance drop off as the data fragments. You'll need to balance the performance against maintenance down-time. I would guess, though, that if you have a weekly maintenance window big enough to handle the CLUSTER, it might be worth doing it that often. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Jeremy Palmer jpal...@linz.govt.nz wrote: My only question is how often will I need to re-cluster the table, because it comes at quite a cost. I probably should have mentioned that the CLUSTER will run faster if the data is already mostly in the right sequence. You'll be doing a nearly sequential pass over the heap, which should minimize seek time, especially if the OS notices the pattern and starts doing sequential read-ahead. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Thanks heaps for the advice. I will do some benchmarks to see how long it takes to cluster all of the database tables. Cheers, Jeremy -Original Message- From: Kevin Grittner [mailto:kevin.gritt...@wicourts.gov] Sent: Tuesday, 25 January 2011 1:02 p.m. To: Jeremy Palmer; Tom Lane Cc: Robert Haas; pgsql-performance@postgresql.org; a...@squeakycode.net Subject: RE: [PERFORM] Possible to improve query plan? Jeremy Palmer jpal...@linz.govt.nz wrote: My only question is how often will I need to re-cluster the table, because it comes at quite a cost. I probably should have mentioned that the CLUSTER will run faster if the data is already mostly in the right sequence. You'll be doing a nearly sequential pass over the heap, which should minimize seek time, especially if the OS notices the pattern and starts doing sequential read-ahead. -Kevin __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Hello, The distribution of the data is that all but 120,000 rows have null values in the _revision_expired column. A shot in the dark - will a partial index on the above column help? http://www.postgresql.org/docs/current/interactive/indexes-partial.html http://en.wikipedia.org/wiki/Partial_index One link with discussion about it... http://www.devheads.net/database/postgresql/general/when-can-postgresql-use-partial-not-null-index-seems-depend-size-clause-even-enable-seqscan.htm Regards, Jayadevan DISCLAIMER: The information in this e-mail and any attachment is intended only for the person to whom it is addressed and may contain confidential and/or privileged material. If you have received this e-mail in error, kindly contact the sender and destroy all copies of the original communication. IBS makes no warranty, express or implied, nor guarantees the accuracy, adequacy or completeness of the information contained in this email or any attachment and is not liable for any errors, defects, omissions, viruses or for resultant loss or damage, if any, direct or indirect.
Re: [PERFORM] Possible to improve query plan?
Which is the type of your application? You can see it on the Performance Whackamole Presentation from Josh Berkus on the PgCon 2009: - Web application - Online Transaction Processing (OLTP) - Data WareHousing (DW) And based on the type of your application, you can configure the postgresql.conf to gain a better performance of your PostgreSQL server. PostgreSQL postgresql.conf baseline: shared_buffers = 25% RAM work_mem = 512K[W] 2 MB[O] 128 MB[D] - but no more that RAM/no_connections maintenance_work_mem = 1/16 RAM checkpoint_segments = 8 [W], 16-64 [O], [D] wal_buffer = 1 MB [W], 8 MB [O], [D] effective_cache_size = 2/3 RAM Regards Ing. Marcos Luís Ortíz Valmaseda Linux User # 418229 PostgreSQL DBA Centro de Tecnologías Gestión de Datos (DATEC) http://postgresql.uci.cu http://www.postgresql.org http://it.toolbox.com/blogs/sql-apprentice - Mensaje original - De: Jeremy Palmer jpal...@linz.govt.nz Para: Andy Colson a...@squeakycode.net CC: pgsql-performance@postgresql.org Enviados: Lunes, 17 de Enero 2011 0:13:25 GMT -05:00 Región oriental EE. UU./Canadá Asunto: Re: [PERFORM] Possible to improve query plan? Hi Andy, Yes important omissions: Server version: 8.4.6 OS Windows Server 2003 Standard Ed :( The work mem is 50mb. I tried setting the work_mem to 500mb, but it didn't make a huge difference in query execution time. But then again the OS disk caching is probably taking over here. Ok here's the new plan with work_mem = 50mb: http://explain.depesz.com/s/xwv And here another plan with work_mem = 500mb: http://explain.depesz.com/s/VmO Thanks, Jeremy -Original Message- From: Andy Colson [mailto:a...@squeakycode.net] Sent: Monday, 17 January 2011 5:57 p.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Possible to improve query plan? Hum.. yeah it looks like it takes no time at all to pull data from the individual indexes, and them bitmap them. I'm not sure what the bitmap heap scan is, or why its slow. Hopefully someone smarter will come along. Also its weird that explain.depesz.com didnt parse and show your entire plan. Hum.. you seem to have ending quotes on some of the lines? One other though: quicksort Memory: 23960kB It needs 20Meg to sort... It could be your sort is swapping to disk. What sort of PG version is this? What are you using for work_mem? (you could try to bump it up a little (its possible to set for session only, no need for server restart) and see if that'd help. And sorry, but its my bedtime, good luck though. -Andy __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Jeremy Palmer wrote: WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40)) - Bitmap Heap Scan on version_crs_coordinate_revision (actual time=70.925..13531.720 rows=149557 loops=1) - BitmapOr (actual time=53.650..53.650 rows=0 loops=1) This plan actually looks pretty good for what you're doing. The Bitmap Index Scans and BitmapOr determine which tuples in the heap need to be visited. The Bitmap Heap Scan then visits the heap pages in physical order (to avoid repeated fetches of the same page and to possibly edge toward sequential access speeds). You don't seem to have a lot of bloat, which could be a killer on this type of query, since the rowcounts from the index scans aren't that much higher than the counts after you check the heap. The only thing I can think of which might help is to CLUSTER the table on whichever of the two indexes used in the plan which is typically more selective for such queries. (In the example query that seems to be idx_crs_coordinate_revision_created.) That might reduce the number of heap pages which need to be accessed and/or put place them close enough that you'll get some sequential readahead. I guess you could also try adjusting effective_io_concurrency upward to see if that helps. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Jeremy Palmer jpal...@linz.govt.nz writes: I've come to a dead end in trying to get a commonly used query to perform better. EXPLAIN SELECT * FROM ( SELECT row_number() OVER (PARTITION BY id ORDER BY _revision_created DESC) as row_number, * FROM version_crs_coordinate_revision WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40) ) ) AS T WHERE row_number = 1; If I'm not mistaken, that's a DB2-ish locution for a query with DISTINCT ON, ie, you're looking for the row with highest _revision_created for each value of id. It might perform well on DB2, but it's going to mostly suck on Postgres --- we don't optimize window-function queries very much at all at the moment. Try writing it with DISTINCT ON instead of a window function, like so: SELECT DISTINCT ON (id) * FROM version_crs_coordinate_revision WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40) ) ORDER BY id, _revision_created DESC; You could also experiment with various forms of GROUP BY if you're loath to use any Postgres-specific syntax. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
It fits a Data Warehousing type application. Apart from work_mem, my other parameters are pretty close to these numbers. I had the work_mem down a little because a noticed some clients were getting out of memory errors with large queries which involved lots of sorting. Thanks Jeremy -Original Message- From: Ing. Marcos Ortiz Valmaseda [mailto:mlor...@uci.cu] Sent: Tuesday, 18 January 2011 2:38 a.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org; Andy Colson Subject: Re: [PERFORM] Possible to improve query plan? Which is the type of your application? You can see it on the Performance Whackamole Presentation from Josh Berkus on the PgCon 2009: - Web application - Online Transaction Processing (OLTP) - Data WareHousing (DW) And based on the type of your application, you can configure the postgresql.conf to gain a better performance of your PostgreSQL server. PostgreSQL postgresql.conf baseline: shared_buffers = 25% RAM work_mem = 512K[W] 2 MB[O] 128 MB[D] - but no more that RAM/no_connections maintenance_work_mem = 1/16 RAM checkpoint_segments = 8 [W], 16-64 [O], [D] wal_buffer = 1 MB [W], 8 MB [O], [D] effective_cache_size = 2/3 RAM Regards Ing. Marcos Luís Ortíz Valmaseda Linux User # 418229 PostgreSQL DBA Centro de Tecnologías Gestión de Datos (DATEC) http://postgresql.uci.cu http://www.postgresql.org http://it.toolbox.com/blogs/sql-apprentice __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Thanks that seems to make the query 10-15% faster :) Cheers jeremy -Original Message- From: Tom Lane [mailto:t...@sss.pgh.pa.us] Sent: Tuesday, 18 January 2011 9:24 a.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Possible to improve query plan? Jeremy Palmer jpal...@linz.govt.nz writes: I've come to a dead end in trying to get a commonly used query to perform better. EXPLAIN SELECT * FROM ( SELECT row_number() OVER (PARTITION BY id ORDER BY _revision_created DESC) as row_number, * FROM version_crs_coordinate_revision WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40) ) ) AS T WHERE row_number = 1; If I'm not mistaken, that's a DB2-ish locution for a query with DISTINCT ON, ie, you're looking for the row with highest _revision_created for each value of id. It might perform well on DB2, but it's going to mostly suck on Postgres --- we don't optimize window-function queries very much at all at the moment. Try writing it with DISTINCT ON instead of a window function, like so: SELECT DISTINCT ON (id) * FROM version_crs_coordinate_revision WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40) ) ORDER BY id, _revision_created DESC; You could also experiment with various forms of GROUP BY if you're loath to use any Postgres-specific syntax. regards, tom lane __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Tom Lane wrote: If I'm not mistaken, that's a DB2-ish locution It could also be a part of the Oracle vernacular. I've seen queries like that running against Oracle RDBMS, too. for a query with DISTINCT ON, ie, you're looking for the row with highest _revision_created for each value of id. It might perform well on DB2, but it's going to mostly suck on Postgres --- we don't optimize window-function queries very much at all at the moment. Hmmm, what optimizations do you have in mind? I thought that window functions are just clever tricks with memory? Anything that can be expected for 9.0x? Try writing it with DISTINCT ON instead of a window function, like so: Wouldn't distinct necessarily bring about the sort/merge? -- Mladen Gogala Sr. Oracle DBA 1500 Broadway New York, NY 10036 (212) 329-5251 http://www.vmsinfo.com The Leader in Integrated Media Intelligence Solutions -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
[PERFORM] Possible to improve query plan?
Hi all, I've come to a dead end in trying to get a commonly used query to perform better. The query is against one table with 10 million rows. This table has been analysed. The table definition is: CREATE TABLE version_crs_coordinate_revision ( _revision_created integer NOT NULL, _revision_expired integer, id integer NOT NULL, cos_id integer NOT NULL, nod_id integer NOT NULL, ort_type_1 character varying(4), ort_type_2 character varying(4), ort_type_3 character varying(4), status character varying(4) NOT NULL, sdc_status character(1) NOT NULL, source character varying(4), value1 numeric(22,12), value2 numeric(22,12), value3 numeric(22,12), wrk_id_created integer, cor_id integer, audit_id integer NOT NULL, CONSTRAINT pkey_version_crs_coordinate_revision PRIMARY KEY (_revision_created, id), CONSTRAINT version_crs_coordinate_revision_revision_created_fkey FOREIGN KEY (_revision_created) REFERENCES revision (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION, CONSTRAINT version_crs_coordinate_revision_revision_expired_fkey FOREIGN KEY (_revision_expired) REFERENCES revision (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION ) WITH ( OIDS=FALSE ); ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN _revision_created SET STATISTICS 1000; ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN _revision_expired SET STATISTICS 1000; ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN id SET STATISTICS 1000; CREATE INDEX idx_crs_coordinate_revision_created ON version.version_crs_coordinate_revision USING btree (_revision_created); CREATE INDEX idx_crs_coordinate_revision_created_expired ON version.version_crs_coordinate_revision USING btree (_revision_created, _revision_expired); CREATE INDEX idx_crs_coordinate_revision_expired ON version.version_crs_coordinate_revision USING btree (_revision_expired); CREATE INDEX idx_crs_coordinate_revision_expired_created ON version.version_crs_coordinate_revision USING btree (_revision_expired, _revision_created); CREATE INDEX idx_crs_coordinate_revision_expired_id ON version.version_crs_coordinate_revision USING btree (_revision_expired, id); CREATE INDEX idx_crs_coordinate_revision_id ON version.version_crs_coordinate_revision USING btree (id); CREATE INDEX idx_crs_coordinate_revision_id_created ON version.version_crs_coordinate_revision USING btree (id, _revision_created); The distribution of the data is that all but 120,000 rows have null values in the _revision_expired column. The query itself that I'm trying to optimise is below: EXPLAIN SELECT * FROM ( SELECT row_number() OVER (PARTITION BY id ORDER BY _revision_created DESC) as row_number, * FROM version_crs_coordinate_revision WHERE ( (_revision_created = 16 AND _revision_expired 16 AND _revision_expired = 40) OR (_revision_created 16 AND _revision_created = 40) ) ) AS T WHERE row_number = 1; Subquery Scan t (cost=170692.25..175678.27 rows=767 width=205) Filter: (t.row_number = 1) - WindowAgg (cost=170692.25..173760.57 rows=153416 width=86) - Sort (cost=170692.25..171075.79 rows=153416 width=86) Sort Key: version_crs_coordinate_revision.id, version_crs_coordinate_revision._revision_created - Bitmap Heap Scan on version_crs_coordinate_revision (cost=3319.13..157477.69 rows=153416 width=86) Recheck Cond: (((_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) Filter: (((_revision_created = 16) AND (_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) - BitmapOr (cost=3319.13..3319.13 rows=154372 width=0) - Bitmap Index Scan on idx_crs_coordinate_revision_expired (cost=0.00..2331.76 rows=111041 width=0) Index Cond: ((_revision_expired 16) AND (_revision_expired = 40)) - Bitmap Index Scan on idx_crs_coordinate_revision_created (cost=0.00..910.66 rows=43331 width=0) Index Cond: ((_revision_created 16) AND (_revision_created = 40)) One thought I have is that maybe the idx_crs_coordinate_revision_expired_created index could be used instead of idx_crs_coordinate_revision_expired. Does anyone have any suggestions what I could do to improve the plan? Or how I could force the use of the idx_crs_coordinate_revision_expired_created index to see if that is better. Thanks Jeremy __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or
Re: [PERFORM] Possible to improve query plan?
On 01/16/2011 09:21 PM, Jeremy Palmer wrote: Hi all, I've come to a dead end in trying to get a commonly used query to perform better. The query is against one table with 10 million rows. This table has been analysed. The table definition is: CREATE TABLE version_crs_coordinate_revision ( _revision_created integer NOT NULL, _revision_expired integer, id integer NOT NULL, cos_id integer NOT NULL, nod_id integer NOT NULL, ort_type_1 character varying(4), ort_type_2 character varying(4), ort_type_3 character varying(4), status character varying(4) NOT NULL, sdc_status character(1) NOT NULL, source character varying(4), value1 numeric(22,12), value2 numeric(22,12), value3 numeric(22,12), wrk_id_created integer, cor_id integer, audit_id integer NOT NULL, CONSTRAINT pkey_version_crs_coordinate_revision PRIMARY KEY (_revision_created, id), CONSTRAINT version_crs_coordinate_revision_revision_created_fkey FOREIGN KEY (_revision_created) REFERENCES revision (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION, CONSTRAINT version_crs_coordinate_revision_revision_expired_fkey FOREIGN KEY (_revision_expired) REFERENCES revision (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE NO ACTION ) WITH ( OIDS=FALSE ); ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN _revision_created SET STATISTICS 1000; ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN _revision_expired SET STATISTICS 1000; ALTER TABLE version.version_crs_coordinate_revision ALTER COLUMN id SET STATISTICS 1000; CREATE INDEX idx_crs_coordinate_revision_created ON version.version_crs_coordinate_revision USING btree (_revision_created); CREATE INDEX idx_crs_coordinate_revision_created_expired ON version.version_crs_coordinate_revision USING btree (_revision_created, _revision_expired); CREATE INDEX idx_crs_coordinate_revision_expired ON version.version_crs_coordinate_revision USING btree (_revision_expired); CREATE INDEX idx_crs_coordinate_revision_expired_created ON version.version_crs_coordinate_revision USING btree (_revision_expired, _revision_created); CREATE INDEX idx_crs_coordinate_revision_expired_id ON version.version_crs_coordinate_revision USING btree (_revision_expired, id); CREATE INDEX idx_crs_coordinate_revision_id ON version.version_crs_coordinate_revision USING btree (id); CREATE INDEX idx_crs_coordinate_revision_id_created ON version.version_crs_coordinate_revision USING btree (id, _revision_created); The distribution of the data is that all but 120,000 rows have null values in the _revision_expired column. The query itself that I'm trying to optimise is below: EXPLAIN SELECT * FROM ( SELECT row_number() OVER (PARTITION BY id ORDER BY _revision_created DESC) as row_number, * FROM version_crs_coordinate_revision WHERE ( (_revision_created= 16 AND _revision_expired 16 AND _revision_expired= 40) OR (_revision_created 16 AND _revision_created= 40) ) ) AS T WHERE row_number = 1; Subquery Scan t (cost=170692.25..175678.27 rows=767 width=205) Filter: (t.row_number = 1) - WindowAgg (cost=170692.25..173760.57 rows=153416 width=86) - Sort (cost=170692.25..171075.79 rows=153416 width=86) Sort Key: version_crs_coordinate_revision.id, version_crs_coordinate_revision._revision_created - Bitmap Heap Scan on version_crs_coordinate_revision (cost=3319.13..157477.69 rows=153416 width=86) Recheck Cond: (((_revision_expired 16) AND (_revision_expired= 40)) OR ((_revision_created 16) AND (_revision_created= 40))) Filter: (((_revision_created= 16) AND (_revision_expired 16) AND (_revision_expired= 40)) OR ((_revision_created 16) AND (_revision_created= 40))) - BitmapOr (cost=3319.13..3319.13 rows=154372 width=0) - Bitmap Index Scan on idx_crs_coordinate_revision_expired (cost=0.00..2331.76 rows=111041 width=0) Index Cond: ((_revision_expired 16) AND (_revision_expired= 40)) - Bitmap Index Scan on idx_crs_coordinate_revision_created (cost=0.00..910.66 rows=43331 width=0) Index Cond: ((_revision_created 16) AND (_revision_created= 40)) One thought I have is that maybe the idx_crs_coordinate_revision_expired_created index could be used instead of idx_crs_coordinate_revision_expired. Does anyone have any suggestions what I could do to improve the plan? Or how I could force the use of the idx_crs_coordinate_revision_expired_created index to see if that is better. Thanks Jeremy First, wow, those are long names... I had a hard time keeping track. Second: you have lots of duplicated indexes. I count _revision_created in 4 indexes? Not sure what other sql you are using, but have you
[PERFORM] Possible to improve query plan?
Hi Andy, Yeah sorry about the long name, there are all generated by function as part of a table versioning system. And yes I placed all possible indexes on the table to see which would be used by the planner. In production I will drop the unused indexes. Yes simple drop the extra index :P I have dropped the index and it made the query slower :( Here is the explain analyse: Subquery Scan t (cost=170692.25..175678.27 rows=767 width=205) (actual time=13762.783..14322.315 rows=106299 loops=1)' Filter: (t.row_number = 1)' - WindowAgg (cost=170692.25..173760.57 rows=153416 width=86) (actual time=13762.774..14208.522 rows=149557 loops=1)' - Sort (cost=170692.25..171075.79 rows=153416 width=86) (actual time=13762.745..13828.584 rows=149557 loops=1)' Sort Key: version_crs_coordinate_revision.id, version_crs_coordinate_revision._revision_created' Sort Method: quicksort Memory: 23960kB - Bitmap Heap Scan on version_crs_coordinate_revision (cost=3319.13..157477.69 rows=153416 width=86) (actual time=70.925..13531.720 rows=149557 loops=1) Recheck Cond: (((_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) Filter: (((_revision_created = 16) AND (_revision_expired 16) AND (_revision_expired = 40)) OR ((_revision_created 16) AND (_revision_created = 40))) - BitmapOr (cost=3319.13..3319.13 rows=154372 width=0) (actual time=53.650..53.650 rows=0 loops=1) - Bitmap Index Scan on idx_crs_coordinate_revision_expired (cost=0.00..2331.76 rows=111041 width=0) (actual time=37.773..37.773 rows=110326 loops=1) Index Cond: ((_revision_expired 16) AND (_revision_expired = 40)) - Bitmap Index Scan on idx_crs_coordinate_revision_created (cost=0.00..910.66 rows=43331 width=0) (actual time=15.872..15.872 rows=43258 loops=1) Index Cond: ((_revision_created 16) AND (_revision_created = 40)) Total runtime: 14359.747 ms http://explain.depesz.com/s/qpL says that the bitmap heap scan is bad. Not sure what to do about it. Thanks, Jeremy -Original Message- From: Andy Colson [mailto:a...@squeakycode.net] Sent: Monday, 17 January 2011 5:22 p.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Possible to improve query plan? First, wow, those are long names... I had a hard time keeping track. Second: you have lots of duplicated indexes. I count _revision_created in 4 indexes? Not sure what other sql you are using, but have you tried one index for one column? PG will be able to Bitmap them together if it thinks it can use more than one. Was that because you were testing? Third: any chance we can get an explain analyze? It give's more info. (Also, have you seen http://explain.depesz.com/) Last: If you wanted to force the index usage, for a test, you could drop the other indexes. I assume this is on a test box so it should be ok. If its live, you could wrap it in a BEGIN ... ROLLBACK (in theory... never tried it myself) -Andy __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
-Original Message- From: Andy Colson [mailto:a...@squeakycode.net] Sent: Monday, 17 January 2011 5:22 p.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Possible to improve query plan? First, wow, those are long names... I had a hard time keeping track. Second: you have lots of duplicated indexes. I count _revision_created in 4 indexes? Not sure what other sql you are using, but have you tried one index for one column? PG will be able to Bitmap them together if it thinks it can use more than one. Was that because you were testing? Third: any chance we can get an explain analyze? It give's more info. (Also, have you seen http://explain.depesz.com/) Last: If you wanted to force the index usage, for a test, you could drop the other indexes. I assume this is on a test box so it should be ok. If its live, you could wrap it in a BEGIN ... ROLLBACK (in theory... never tried it myself) -Andy On 01/16/2011 10:43 PM, Jeremy Palmer wrote: Hi Andy, Yeah sorry about the long name, there are all generated by function as part of a table versioning system. And yes I placed all possible indexes on the table to see which would be used by the planner. In production I will drop the unused indexes. Yes simple drop the extra index :P I have dropped the index and it made the query slower :( Here is the explain analyse: Subquery Scan t (cost=170692.25..175678.27 rows=767 width=205) (actual time=13762.783..14322.315 rows=106299 loops=1)' Filter: (t.row_number = 1)' - WindowAgg (cost=170692.25..173760.57 rows=153416 width=86) (actual time=13762.774..14208.522 rows=149557 loops=1)' - Sort (cost=170692.25..171075.79 rows=153416 width=86) (actual time=13762.745..13828.584 rows=149557 loops=1)' Sort Key: version_crs_coordinate_revision.id, version_crs_coordinate_revision._revision_created' Sort Method: quicksort Memory: 23960kB - Bitmap Heap Scan on version_crs_coordinate_revision (cost=3319.13..157477.69 rows=153416 width=86) (actual time=70.925..13531.720 rows=149557 loops=1) Recheck Cond: (((_revision_expired 16) AND (_revision_expired= 40)) OR ((_revision_created 16) AND (_revision_created= 40))) Filter: (((_revision_created= 16) AND (_revision_expired 16) AND (_revision_expired= 40)) OR ((_revision_created 16) AND (_revision_created= 40))) - BitmapOr (cost=3319.13..3319.13 rows=154372 width=0) (actual time=53.650..53.650 rows=0 loops=1) - Bitmap Index Scan on idx_crs_coordinate_revision_expired (cost=0.00..2331.76 rows=111041 width=0) (actual time=37.773..37.773 rows=110326 loops=1) Index Cond: ((_revision_expired 16) AND (_revision_expired= 40)) - Bitmap Index Scan on idx_crs_coordinate_revision_created (cost=0.00..910.66 rows=43331 width=0) (actual time=15.872..15.872 rows=43258 loops=1) Index Cond: ((_revision_created 16) AND (_revision_created= 40)) Total runtime: 14359.747 ms http://explain.depesz.com/s/qpL says that the bitmap heap scan is bad. Not sure what to do about it. Thanks, Jeremy Hum.. yeah it looks like it takes no time at all to pull data from the individual indexes, and them bitmap them. I'm not sure what the bitmap heap scan is, or why its slow. Hopefully someone smarter will come along. Also its weird that explain.depesz.com didnt parse and show your entire plan. Hum.. you seem to have ending quotes on some of the lines? One other though: quicksort Memory: 23960kB It needs 20Meg to sort... It could be your sort is swapping to disk. What sort of PG version is this? What are you using for work_mem? (you could try to bump it up a little (its possible to set for session only, no need for server restart) and see if that'd help. And sorry, but its my bedtime, good luck though. -Andy -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Possible to improve query plan?
Hi Andy, Yes important omissions: Server version: 8.4.6 OS Windows Server 2003 Standard Ed :( The work mem is 50mb. I tried setting the work_mem to 500mb, but it didn't make a huge difference in query execution time. But then again the OS disk caching is probably taking over here. Ok here's the new plan with work_mem = 50mb: http://explain.depesz.com/s/xwv And here another plan with work_mem = 500mb: http://explain.depesz.com/s/VmO Thanks, Jeremy -Original Message- From: Andy Colson [mailto:a...@squeakycode.net] Sent: Monday, 17 January 2011 5:57 p.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Possible to improve query plan? Hum.. yeah it looks like it takes no time at all to pull data from the individual indexes, and them bitmap them. I'm not sure what the bitmap heap scan is, or why its slow. Hopefully someone smarter will come along. Also its weird that explain.depesz.com didnt parse and show your entire plan. Hum.. you seem to have ending quotes on some of the lines? One other though: quicksort Memory: 23960kB It needs 20Meg to sort... It could be your sort is swapping to disk. What sort of PG version is this? What are you using for work_mem? (you could try to bump it up a little (its possible to set for session only, no need for server restart) and see if that'd help. And sorry, but its my bedtime, good luck though. -Andy __ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. __ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
