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
