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?
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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
