> If I have 2 separate processes, 1 of which will attempt to Read and Write a > Database (Process A) > and the 2nd which will only Read the database (Process B), then if Process A > is in the middle of a Write when Process B tries to read what will happen?
If Process A is in the middle of writing transaction but has not actually written anything to disk yet (all changes are in cache) then Process B will proceed reading unlocked. If Process A is in the middle of committing transaction or it has written some changes to disk (there're so many changes that they don't fit into cache) then API in Process B will return SQLITE_BUSY error. But only unless you've called sqlite3_busy_timeout() with non-zero value. In the latter case Process B will return SQLITE_BUSY only after mentioned timeout has gone and Process A does not finish transaction yet. And when SQLITE_BUSY is returned then indeed it's up to you to try again later. > And Vice versa, What happens if Process B is reading while A tries to write? Process A will continue unblocked until it will have to actually write to disk. At this point it will wait for Process B to finish its reading and after that it will actually write everything it needs. Pavel On Fri, Aug 7, 2009 at 11:50 AM, JimmyKryptonite<[email protected]> wrote: > > I'm looking to start a project using SQLite to handle some database > transactions. I have question about how SQLite handles Concurrency. I read > up on SQLite.org about the file locking and concurrency but I didn't really > get the info I wanted (at least I didn't walk away with an answer in the > terms I wanted it). > > My question is the following: > > If I have 2 separate processes, 1 of which will attempt to Read and Write a > Database (Process A) > and the 2nd which will only Read the database (Process B), then if Process A > is in the middle of a Write when Process B tries to read what will happen? > Will the Read request be blocked and Process B will wait or will SQLite > return some kind of Busy Error Code to process B and it is up to Process B > to try again later? > > And Vice versa, What happens if Process B is reading while A tries to write? > Same answer as above? > > I'm very much a newbie to SQLite so patience is requested. > > Thanks in advance > -- > View this message in context: > http://www.nabble.com/Concurrency-Question-tp24867278p24867278.html > Sent from the SQLite mailing list archive at Nabble.com. > > _______________________________________________ > sqlite-users mailing list > [email protected] > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
