Although programmatically easily done, from the SQLite point of view, what if that query, sans LIMIT, were a subquery, and the limit was put out on the outside? Would the inner query execute, use all the threads, then return just one row on the outer?
On Fri, Sep 16, 2016 at 7:29 AM, Richard Hipp <d...@sqlite.org> wrote: > On 8/14/16, Венцислав Русев <ven...@proxima-3.com> wrote: > > My computer has 4 cores. I have compile sqlite like this "gcc > > -DSQLITE_MAX_WORKER_THREADS=4 -DSQLITE_DEFAULT_WORKER_THREADS=4 shell.c > > sqlite3.c -lpthread -ldl -o sqlite3". I made some tests and found that > > "pragma threads = 4" doesn't decrease runtime of the query that sorts 1 > > milion records. > > > > SQLite version 3.8.8 > > sqlite> pragma threads; > > 4 > > sqlite> CREATE TABLE event ( > > ID INTEGER PRIMARY KEY NOT NULL, > > date INTEGER NOT NULL, > > value INTEGER NOT NULL ); > > sqlite> EXPLAIN QUERY PLAN SELECT ID FROM event ORDER BY date LIMIT 1; > > The algorithm used for "ORDER BY ... LIMIT N" uses much less memory > than a full-up "ORDER BY" because is only keeps track of the top N > entries seen so far, discarding the rest. But it also only uses a > single thread. If you want multiple threads to be used, you'll need > to drop the LIMIT, though I imagine that would defeat your purpose, > no? > > -- > D. Richard Hipp > d...@sqlite.org > _______________________________________________ > sqlite-users mailing list > sqlite-users@mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
