On Nov 19, 2008, at 3:08 AM, Jens Miltner wrote: > Hi, > > we're seeing terrible performance problems when fetching data from one > of our tables: > The table contains roughly 1.2 Million rows and a plain "SELECT > COUNT(*) FROM t" query takes 8 minutes to finish.
That's because "SELECT count(*) FROM t" has to read and count every row in the table - all 1.2 million rows. And this involves reading all 1.2 million rows from disk. If each row is 100 bytes in size, that involves reading 120MB. An SQLite database does *not* maintain the number of rows in a table as separate metadata. Many client/server database engines do maintain such metadata. When I was designing the SQLite file format, I deliberately choose to omit such metadata because including it would slow down inserts and deletes. If you frequently need to know how many rows are in a certain table, use insert and delete triggers to maintain the count yourself in a separate table. Then just read out the count from the separate table when you need it, rather than recomputing it by reading all 1.2 million rows of the original table. D. Richard Hipp [EMAIL PROTECTED] _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
