Re: [sqlite] ROWID-based queries slow in FTS db
Thank you for the quick fix and the info, I will wait for 3.8.9 to trickle down into DBD::SQLite. AF Dan Kennedy írta: >On 01/30/2015 10:49 PM, Dominique Devienne wrote: >> On Fri, Jan 30, 2015 at 4:38 PM, Dan Kennedy wrote: >> >>> On 01/29/2015 02:29 AM, farkas andras wrote: >>> [...] but searches based on ROWID are atrociously slow and hog massive amounts of memory [...] >>> Looks like range constraints on rowids were only taken into account when >>> there was also a MATCH term in the WHERE clause. Now fixed here: >>> >>>http://www.sqlite.org/src/info/85dc12625d300f >>> >>> The fix should be in 3.8.9. >> >> Just curious Dan. The tests added do not seem to check the query plans >> despite the report being about a performance issue. I only skimmed them, >> and I'm unfamiliar with TCL and the exact specifics of SQLite testing, >> so I >> could well have missed them, but I do recall seen other perf tests checking >> execution plans, in addition to checking correctness. Did I miss them? > >Fair point. It would be better if there were tests to show that the >queries were being correctly optimized. > >But the change was fairly trivial, and I didn't think there was much >chance that it would fail to optimize the queries correctly. Also, it's >a pretty obscure optimization (one complaint in how many years?), so I >figured it wasn't all that important. Finally it's fiddly to test in >this case, as the EXPLAIN QUERY PLAN (or even EXPLAIN) output is not >sufficient to figure out if it's working properly or not. So I just >checked by hand that the optimization is working. > >On the other hand, that the change could contain some bug related to >integer overflow or some other boundary condition is a real risk. So the >tests focus on that. > >Dan. > > >___ >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] ROWID-based queries slow in FTS db
On 01/30/2015 10:49 PM, Dominique Devienne wrote: On Fri, Jan 30, 2015 at 4:38 PM, Dan Kennedy wrote: On 01/29/2015 02:29 AM, farkas andras wrote: [...] but searches based on ROWID are atrociously slow and hog massive amounts of memory [...] Looks like range constraints on rowids were only taken into account when there was also a MATCH term in the WHERE clause. Now fixed here: http://www.sqlite.org/src/info/85dc12625d300f The fix should be in 3.8.9. Just curious Dan. The tests added do not seem to check the query plans despite the report being about a performance issue. I only skimmed them, and I'm unfamiliar with TCL and the exact specifics of SQLite testing, so I could well have missed them, but I do recall seen other perf tests checking execution plans, in addition to checking correctness. Did I miss them? Fair point. It would be better if there were tests to show that the queries were being correctly optimized. But the change was fairly trivial, and I didn't think there was much chance that it would fail to optimize the queries correctly. Also, it's a pretty obscure optimization (one complaint in how many years?), so I figured it wasn't all that important. Finally it's fiddly to test in this case, as the EXPLAIN QUERY PLAN (or even EXPLAIN) output is not sufficient to figure out if it's working properly or not. So I just checked by hand that the optimization is working. On the other hand, that the change could contain some bug related to integer overflow or some other boundary condition is a real risk. So the tests focus on that. Dan. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] ROWID-based queries slow in FTS db
On Fri, Jan 30, 2015 at 4:38 PM, Dan Kennedy wrote: > On 01/29/2015 02:29 AM, farkas andras wrote: > >> [...] but searches based on ROWID are atrociously slow and hog massive >> amounts of memory [...] >> > > Looks like range constraints on rowids were only taken into account when > there was also a MATCH term in the WHERE clause. Now fixed here: > > http://www.sqlite.org/src/info/85dc12625d300f > > The fix should be in 3.8.9. Just curious Dan. The tests added do not seem to check the query plans despite the report being about a performance issue. I only skimmed them, and I'm unfamiliar with TCL and the exact specifics of SQLite testing, so I could well have missed them, but I do recall seen other perf tests checking execution plans, in addition to checking correctness. Did I miss them? Thanks, --DD ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] ROWID-based queries slow in FTS db
On 01/29/2015 02:29 AM, farkas andras wrote: Hi all, I'm using FTS through DBD::SQLite (perl) to query large text databases (~10GB, ~10 million records). The regular FTS MATCH searches work fine (they usually run under a second), but searches based on ROWID are atrociously slow and hog massive amounts of memory. I'm trying to retrieve a couple of adjacent rows like so: my $q_c = $dbh->prepare( "SELECT * FROM ftstable WHERE (ROWID BETWEEN 1000 AND 1040)" ); # my $q_c = $dbh->prepare( "SELECT * FROM ftstable LIMIT 1040 OFFSET 1000" ); # tried this too, it isn't any better $q_c->execute(); The execute takes several minutes and uses ~600 MB of memory. Now, http://www.sqlite.org/changes.html writes that: 3.8.1: FTS4 queries are better able to make use of docid<$limit constraints to limit the amount of I/O required There's also this thread, indicating that rowid searches on FTS databases are optimized: http://sqlite.1065341.n5.nabble.com/FTS-full-text-query-vs-query-by-rowid-td77534.html I was using 3.7.x so I updated DBD::SQLite and that got me up to SQLite 3.8.7, but I see no significant improvement. Explain query gives the same result as the linked thread: 0|0|0|SCAN TABLE tmdata VIRTUAL TABLE INDEX 393216. Maybe there is a better way to write the query? If not, is there any hope that this will get fixed? Looks like range constraints on rowids were only taken into account when there was also a MATCH term in the WHERE clause. Now fixed here: http://www.sqlite.org/src/info/85dc12625d300f The fix should be in 3.8.9. Dan. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
