Hi, I am having some unexpected locking issues with SQLite.
I have a desktop application that uses SQLite. The application has a low
priority worker thread that is constantly analyzing/adding/updating/deleting
records in the database. The main application thread mainly reads from the
database but also does some updating/deleting. Both threads have their own
SQLite connection.
My problem is that when I do updates in the main application thread I quite
often fail with a return value of SQLITE_BUSY. I have messed around with
busy_timeouts and busy_handlers without much success. My current busy
handler (culled either from this list or the web) is:
int busyHandler(void *pArg1, int iPriorCalls)
{
// sleep if handler has been called less than threshold value
if (iPriorCalls < 20)
{
// adding a random value here greatly reduces locking
if (pArg1 < 0)
Sleep((rand() % 500) + 400);
else Sleep(500);
return 1;
}
// have sqlite3_exec immediately return SQLITE_BUSY
return 0;
}
If I increase the transaction size on the low priority thread I get more
update failures on the main thread.
My schema is fairly simple and my tables contain < 90,000 rows. It would
seem to me that with just two threads and this busy handler I should never
(or very rarely) get SQLITE_BUSY.
My theory is that the main application thread is getting locked out because
it is waiting for the low priority thread to release the lock on the
database. Meanwhile something else is happing on the machine at a higher
priority and not letting the low priority thread back in to finish the
transaction and release the lock.
Does this sound reasonable and is there a good way of dealing with this
situation? Should I try to increase the priority of the background thread
when I get a lock? Or is there some way to make sure that transactions in
the low priority thread are executed all at once without interruption?
Thanks for your time,
--
BP
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