On Wed, Aug 10, 2011 at 1:35 PM, Sreekumar TP <sreekumar...@gmail.com>wrote:
> Ok, its getting a bit clear. > If there is only one process that is writing to the database, but has more > than one process that reads the database, the locking mode can still be > exclusive ? > PRAGMA locking_mode=EXCLUSIVE; means "exclusive'. Only one process can access. If you have one reader and many writers, consider PRAGMA journal_mode=WAL; > If the other process opens the db connection as read_only, will the hot > journal check be still done (during queries operations of the second > process)? > How is the second process suppose to know whether or not the other process used read_only? > > > > > On Wed, Aug 10, 2011 at 10:54 PM, Richard Hipp <d...@sqlite.org> wrote: > > > On Wed, Aug 10, 2011 at 1:09 PM, Simon Slavin <slav...@bigfraud.org> > > wrote: > > > > > > > > On 10 Aug 2011, at 6:01pm, Sreekumar TP wrote: > > > > > > > Thanks for the explanation. The journal mode was OFF which means > there > > > is > > > > no journal file created. So why is it the check still performed ? > > > > > > Because the journal mode might have been 'ON' the last time that > > database > > > was used. > > > > > > > More importantly, the journal mode might be 'ON' in the other process > that > > crashed in the middle of a transaction. > > > > > > > > > > > > > On Wed, Aug 10, 2011 at 10:24 PM, Richard Hipp <d...@sqlite.org> > wrote: > > > > > > > >> On Wed, Aug 10, 2011 at 12:40 PM, Sreekumar TP < > > sreekumar...@gmail.com > > > >>> wrote: > > > >> > > > >>> The 179148 failures on 'access' system call is due to access check > of > > > two > > > >>> files - the journal file and the wal-file. > > > > > > Well, the file is obviously not being opened 179148 times. I thought > it > > > checked for these files only when sqlite3_open() was being run. Is it > > > checking for these files every time a command is executed ? Surely > that > > is > > > unnecessary and a source of a large reduction in speed. > > > > > > > SQLite must check for hot journals at the start of each transaction. > > > > Or, more precisely, SQLite must check for hot journals whenever it starts > > reading the database again after a period of time when another process > > might > > have been writing to the database (and might have crashed while writing). > > > > That's when PRAGMA locking_mode=EXCLUSIVE blocks the hot-journal checks. > > If > > your process has exclusive access to the database, it is not possible for > > another process to write to the database (and crash in the middle of > > writing). > > > > > > > > > > > > Simon. > > > _______________________________________________ > > > sqlite-users mailing list > > > sqlite-users@sqlite.org > > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > > > > > > > > > > > -- > > D. Richard Hipp > > d...@sqlite.org > > _______________________________________________ > > sqlite-users mailing list > > sqlite-users@sqlite.org > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
