On 13/06/2011, at 6:49 PM, Ian Hardingham wrote: > As was being discussed yesterday, I have four processes accessing the > same database file. When they perform an sqlite action, I wish them to > block if the DB is not available. SQLite does not block if it finds the > db busy or locked, it returns an error code.
Short answer: Make sure each process accesses the SQLite database inside their own transaction. If the transaction contains a command that will change the database (eg delete, update or insert), then use "begin immediate" to start the transaction, so that it won't proceed unless it has unchallenged access to the database. For other transactions, which are making no changes (ie just select), use "begin deferred" (which is the default behavior for plain "begin"). The logic is that only one writing (update, delete or insert) transaction at a time will be given a reserved lock. Each writing transaction must wait their turn and will not start until they can have "immediate" reserved access. Meanwhile, multiple read-only (select) transactions can happily start and finish at will. For more info on transaction types, see: http://www.sqlite.org/lang_transaction.html Set the timeouts as long as is reasonable for the queue of other write transactions to finish. Tom Brodhurst-Hill BareFeetWare -- Comparison of SQLite GUI tools: http://www.barefeetware.com/sqlite/compare/?ml -- iPhone/iPad/iPod and Mac software development, specialising in databases develo...@barefeetware.com _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
