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> -----Original Message----- > From: sqlite-users-boun...@mailinglists.sqlite.org [mailto:sqlite-users- > boun...@mailinglists.sqlite.org] On Behalf Of Yuri > Sent: Friday, 17 June, 2016 14:02 > To: SQLite mailing list > Subject: [sqlite] Why the parallel read of DB is faster with separate > connections per thread? > > I have a fairly large DB that I need to only read (not write) as fast as > possible. I open DB with flags > SQLITE_OPEN_READONLY|SQLITE_OPEN_PRIVATECACHE and then run select > queries in 8 threads. > > When each thread opens its own connection, DB is read in 8 wallclock > seconds using 23 user seconds. > > When DB connection is shared by threads, though, the process reads the > same data in 17 wallclock seconds using 20 user seconds, much slower > overall, killing the parallelism benefit. > > > Reusing RO connection for some reason makes threads wait for each other > too much. What makes the single connection to slow the process down? > > > In an attempt to speed it up as much as possible, I was trying to first > copy into :memory: db, so that threads would read only from memory, but > this requires the shared connection and it is slower. > > > sqlite3-3.12.2 > > > Yuri > > _______________________________________________ > 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
