On Thu, Oct 15, 2009 at 10:57:11PM -0400, Pavel Ivanov scratched on the wall: > You're definitely talking about some bug in your application or some > misunderstanding about how SQLite should work. SQLite by itself never > causes any deadlocks.
As I understand it, that's not exactly true. SQLite can and does deadlock. It also tries to detect when this is happening and encourage the application to break the deadlock. This depends on the applications' cooperation, however. From <http://www.sqlite.org/c3ref/busy_handler.html> : Consider a scenario where one process is holding a read lock that it is trying to promote to a reserved lock and a second process is holding a reserved lock that it is trying to promote to an exclusive lock. The first process cannot proceed because it is blocked by the second and the second process cannot proceed because it is blocked by the first. If both processes invoke the busy handlers, neither will make any progress. Therefore, SQLite returns SQLITE_BUSY for the first process, hoping that this will induce the first process to release its read lock and allow the second process to proceed. This implies that SQLite can figure out what is going on, but will not automatically rollback a transaction and break the deadlock by itself. That also implies that if an application goes into an infinite "try again" loop whenever it gets an SQLITE_BUSY return code, the deadlock may persist. The page <http://www.sqlite.org/lang_transaction.html> is clear that this is the expected behavior, on behalf of the application: "It is recommended that applications respond to the errors listed above [including SQLITE_BUSY] by explicitly issuing a ROLLBACK command." In short, you can poke at a SQLITE_BUSY state for a bit, but fairly soon you should give up and back all the way out. If you don't, a deadlock is possible. But that would be considered an application bug, not an SQLite bug. -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Our opponent is an alien starship packed with atomic bombs. We have a protractor." "I'll go home and see if I can scrounge up a ruler and a piece of string." --from Anathem by Neal Stephenson _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
