Re: [sqlite] Sqlite uses a lot of memory during a delete operation
Maybe LIMIT clause can be used. Please check the below link. http://www.sqlite.org/lang_delete.html Regards Shankar On Wed, Sep 9, 2009 at 5:16 PM, P Kishorwrote: > On Tue, Sep 8, 2009 at 10:48 PM, Benjamin Rutt wrote: > > On Mon, Sep 7, 2009 at 12:28 PM, P Kishor wrote: > > > >> Find out if the DELETEion is chewing up the memory or the SELECTion. Try > >> > >> SELECT * FROM old_conns WHERE "end" >= strftime('%s', 'now', '-7 days'); > >> > >> If the above is quick, you can simply create a new table with that, > >> and then drop the old table. > >> > >> CREATE TABLE new_conns AS SELECT * FROM old_conns WHERE "end" >= > >> strftime('%s', 'now', '-7 days'); > >> > >> DROP TABLE old_conns; > >> > > > > When I do the select as you suggested, the process remains contained to a > > small amount of memory, which is good, but the result set from the select > is > > huge. As I wrote originally, about 50% of the table would be deleted by > my > > delete, so about 50% of the table would be selected were I to use your > > select. So yes, I could create a tmp table and insert into it, add the > > missing index, drop the old table, and rename the old to the new. > > > Well, I would recreate indexes as the last step in the process, after > I have dropped the old table. Indexes are probably significant in > size. > > > This > > would work, but seems to me is quite an expensive hack. It would also > > require 200% of the original table space on disk in the worst case, and > may > > necessitate an extra vacuum operation after the fact to conserve disk > space > > (the original db file is 8GB so I suspect it would double in size to 16GB > in > > the worst case). So it is a workaround, but not a cheap one. > > Yes, but I am not sure if you actually tried the entire process and > measured the space and time tradeoffs. From your statements above, it > seems you haven't yet tried it since you write, "I could create a tmp > table..." > > I would be curious to see if you get a decent space time tradeoff or > not. It may or may not be worth it. > > > > > > Thanks. > > ___ > > sqlite-users mailing list > > sqlite-users@sqlite.org > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > > > > > > -- > Puneet Kishor > ___ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
On Tue, Sep 8, 2009 at 10:48 PM, Benjamin Ruttwrote: > On Mon, Sep 7, 2009 at 12:28 PM, P Kishor wrote: > >> Find out if the DELETEion is chewing up the memory or the SELECTion. Try >> >> SELECT * FROM old_conns WHERE "end" >= strftime('%s', 'now', '-7 days'); >> >> If the above is quick, you can simply create a new table with that, >> and then drop the old table. >> >> CREATE TABLE new_conns AS SELECT * FROM old_conns WHERE "end" >= >> strftime('%s', 'now', '-7 days'); >> >> DROP TABLE old_conns; >> > > When I do the select as you suggested, the process remains contained to a > small amount of memory, which is good, but the result set from the select is > huge. As I wrote originally, about 50% of the table would be deleted by my > delete, so about 50% of the table would be selected were I to use your > select. So yes, I could create a tmp table and insert into it, add the > missing index, drop the old table, and rename the old to the new. Well, I would recreate indexes as the last step in the process, after I have dropped the old table. Indexes are probably significant in size. > This > would work, but seems to me is quite an expensive hack. It would also > require 200% of the original table space on disk in the worst case, and may > necessitate an extra vacuum operation after the fact to conserve disk space > (the original db file is 8GB so I suspect it would double in size to 16GB in > the worst case). So it is a workaround, but not a cheap one. Yes, but I am not sure if you actually tried the entire process and measured the space and time tradeoffs. From your statements above, it seems you haven't yet tried it since you write, "I could create a tmp table..." I would be curious to see if you get a decent space time tradeoff or not. It may or may not be worth it. > > Thanks. > ___ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- Puneet Kishor ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
On Mon, Sep 7, 2009 at 12:28 PM, P Kishorwrote: > Find out if the DELETEion is chewing up the memory or the SELECTion. Try > > SELECT * FROM old_conns WHERE "end" >= strftime('%s', 'now', '-7 days'); > > If the above is quick, you can simply create a new table with that, > and then drop the old table. > > CREATE TABLE new_conns AS SELECT * FROM old_conns WHERE "end" >= > strftime('%s', 'now', '-7 days'); > > DROP TABLE old_conns; > When I do the select as you suggested, the process remains contained to a small amount of memory, which is good, but the result set from the select is huge. As I wrote originally, about 50% of the table would be deleted by my delete, so about 50% of the table would be selected were I to use your select. So yes, I could create a tmp table and insert into it, add the missing index, drop the old table, and rename the old to the new. This would work, but seems to me is quite an expensive hack. It would also require 200% of the original table space on disk in the worst case, and may necessitate an extra vacuum operation after the fact to conserve disk space (the original db file is 8GB so I suspect it would double in size to 16GB in the worst case). So it is a workaround, but not a cheap one. Thanks. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
Tried that, it didn't help. On Mon, Sep 7, 2009 at 11:40 AM, Simon Slavinwrote: > > On 7 Sep 2009, at 4:01pm, Benjamin Rutt wrote: > > > Good idea. Tried that, though, and it didn't help - the process > > still grew > > and grew in memory. > > Just in case, change the name of your column 'end' to something that > isn't a keyword. > > Simon. > ___ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- Benjamin Rutt ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
On Sun, Sep 6, 2009 at 5:23 PM, Benjamin Ruttwrote: > I noticed sqlite is using a lot of memory (up to 300MB before it hits a data > segment size ulimit and fails) during a delete operation. This is > reproducable using the 'sqlite3' executable distributed with sqlite. My > platform is sqlite 3.6.13 with the OS being solaris 10 on sparc > architecture, but the problem is reproducible on linux as well if I copy the > database file to a linux machine. The relevant table schema is as follows: > > CREATE TABLE old_conns (a TEXT, b INTEGER, c TEXT, d TEXT, e TEXT, start > INTEGER, end INTEGER, f INTEGER, g INTEGER, h INTEGER, i INTEGER) > CREATE INDEX end_idx ON old_conns ( end ) > > The delete operation fails as follows: > > sqlite> DELETE FROM old_conns WHERE end < strftime('%s', 'now', '-7 > days'); > SQL error: out of memory > Find out if the DELETEion is chewing up the memory or the SELECTion. Try SELECT * FROM old_conns WHERE "end" >= strftime('%s', 'now', '-7 days'); If the above is quick, you can simply create a new table with that, and then drop the old table. CREATE TABLE new_conns AS SELECT * FROM old_conns WHERE "end" >= strftime('%s', 'now', '-7 days'); DROP TABLE old_conns; Of course, do change the name of the column "end" to something other than a reserved keyword. > I would have thought that the memory used would be small for a delete > operation, but maybe there's some large temporary table being created in > memory for this operation? Perhaps the fact that it has to update the index > along with the delete is causing memory usage where it wouldn't otherwise if > there was no index? It still fails if I set "pragma temp_store=1" which I > believe instructs sqlite to put temporary tables on disk instead of memory. > > The sqlite file observable via 'ls -al' is about 8GB in size (although I've > never vacuumed it), and the total size of the 'old_conns' table is about 68 > million rows. I expect roughly 50% of them would be deleted by the above > delete operation, but I have yet to see it succeed. > > Is there any obvious explanation for this? Any administrative controls I > can use to prevent it from happening? > > Thanks. > -- > Benjamin Rutt > ___ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- Puneet Kishor http://www.punkish.org Carbon Model http://carbonmodel.org Charter Member, Open Source Geospatial Foundation http://www.osgeo.org Science Commons Fellow, http://sciencecommons.org/about/whoweare/kishor Nelson Institute, UW-Madison http://www.nelson.wisc.edu --- Assertions are politics; backing up assertions with evidence is science === ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
On 7 Sep 2009, at 4:01pm, Benjamin Rutt wrote: > Good idea. Tried that, though, and it didn't help - the process > still grew > and grew in memory. Just in case, change the name of your column 'end' to something that isn't a keyword. Simon. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
> > You're doing this on 68 million rows. While it probably shouldn't > give an error in this way, I can imagine various things that might > cause it. > > To help with debugging, and also as a suggested fix until the problem > can be investigated, could you pre-calculate your 'strftime' value, > and use that in the command instead ? It would help to see whether > the calculation of this is the thing causing the error. You can use > SQLite to do the calculation > > sqlite> SELECT strftime('%s', 'now', '-7 days'); > 1251679819 > > if you like. Then take whatever value you get and plug it into the > DELETE command: > Good idea. Tried that, though, and it didn't help - the process still grew and grew in memory. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Sqlite uses a lot of memory during a delete operation
On 6 Sep 2009, at 11:23pm, Benjamin Rutt wrote: > I noticed sqlite is using a lot of memory (up to 300MB before it > hits a data > segment size ulimit and fails) during a delete operation. This is > reproducable using the 'sqlite3' executable distributed with > sqlite. My > platform is sqlite 3.6.13 with the OS being solaris 10 on sparc > architecture, but the problem is reproducible on linux as well if I > copy the > database file to a linux machine. The relevant table schema is as > follows: > > CREATE TABLE old_conns (a TEXT, b INTEGER, c TEXT, d TEXT, e TEXT, > start > INTEGER, end INTEGER, f INTEGER, g INTEGER, h INTEGER, i INTEGER) > CREATE INDEX end_idx ON old_conns ( end ) > > The delete operation fails as follows: > > sqlite> DELETE FROM old_conns WHERE end < strftime('%s', 'now', '-7 > days'); > SQL error: out of memory You're doing this on 68 million rows. While it probably shouldn't give an error in this way, I can imagine various things that might cause it. To help with debugging, and also as a suggested fix until the problem can be investigated, could you pre-calculate your 'strftime' value, and use that in the command instead ? It would help to see whether the calculation of this is the thing causing the error. You can use SQLite to do the calculation sqlite> SELECT strftime('%s', 'now', '-7 days'); 1251679819 if you like. Then take whatever value you get and plug it into the DELETE command: sqlite> DELETE FROM old_conns WHERE end < 1251679819; I have an observation though I don't think it's related. You're using the word 'end' as a column name. In the table on http://www.sqlite.org/lang_keywords.html it's listed as a keyword. You might want to avoid this in case it causes problems in the future, when you try to use the word in a context where it's ambiguous. Perhaps use conn_start and conn_end ? Simon. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
[sqlite] Sqlite uses a lot of memory during a delete operation
I noticed sqlite is using a lot of memory (up to 300MB before it hits a data segment size ulimit and fails) during a delete operation. This is reproducable using the 'sqlite3' executable distributed with sqlite. My platform is sqlite 3.6.13 with the OS being solaris 10 on sparc architecture, but the problem is reproducible on linux as well if I copy the database file to a linux machine. The relevant table schema is as follows: CREATE TABLE old_conns (a TEXT, b INTEGER, c TEXT, d TEXT, e TEXT, start INTEGER, end INTEGER, f INTEGER, g INTEGER, h INTEGER, i INTEGER) CREATE INDEX end_idx ON old_conns ( end ) The delete operation fails as follows: sqlite> DELETE FROM old_conns WHERE end < strftime('%s', 'now', '-7 days'); SQL error: out of memory I would have thought that the memory used would be small for a delete operation, but maybe there's some large temporary table being created in memory for this operation? Perhaps the fact that it has to update the index along with the delete is causing memory usage where it wouldn't otherwise if there was no index? It still fails if I set "pragma temp_store=1" which I believe instructs sqlite to put temporary tables on disk instead of memory. The sqlite file observable via 'ls -al' is about 8GB in size (although I've never vacuumed it), and the total size of the 'old_conns' table is about 68 million rows. I expect roughly 50% of them would be deleted by the above delete operation, but I have yet to see it succeed. Is there any obvious explanation for this? Any administrative controls I can use to prevent it from happening? Thanks. -- Benjamin Rutt ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users