More than one concurrent writer is not supported. WAL mode only allows readers to see the state of the db as it was at the start of their transaction while writers' changes are written to the WAL file.
Threadsafe refers to the interoperation of multiple threads within a single process. Single thread means that only one thread of a process can use SQLite at any time. Multithread means that several threads within a single proces may cal SQLite, but only one thread at a time is allowed per connection. Serilaized means that any thread can call SQLite for any connection at any time, but the second caller will block until the first one returns from the library. What you tested is multiple processes accessing the same db file. This uses the normal locking protocol. The first process to establish a write lock will proceed with its work until the transaction ends (commit or rollback), releasing the lock that the second process was waiting for. Only then will the second process be able to continue. -----Ursprüngliche Nachricht----- Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im Auftrag von Nick Gesendet: Dienstag, 06. Februar 2018 12:52 An: sqlite-users@mailinglists.sqlite.org Betreff: [EXTERNAL] [sqlite] Question about threadsafe I use sqlite 3.16.2 in Android system and I have configured journal_mode=WAL, threadsafe=1. My understanding is that: WAL => readers and only one writer can run at the same time. threadsafe=1 => mutex is used in serialized mode so that two writers is supported. Is it correct? But I ran a simple test: Two processes will run sqlite3_open() respectively to open the same db. Then both of the two processes will insert 10000 records(in Transaction) into the db simultaneously. But I find that: Process A begin Process A insert Process B begin Process B insert Process A end Process B end Which I guess the Process B did not sleep at all? And the count of records is less than 20000 at last. So I think multiple write threads is not allowed even though I use threadsafe=1 in wal mode? -- Sent from: http://sqlite.1065341.n5.nabble.com/ _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users ___________________________________________ Gunter Hick | Software Engineer | Scientific Games International GmbH | Klitschgasse 2-4, A-1130 Vienna | FN 157284 a, HG Wien, DVR: 0430013 | (O) +43 1 80100 - 0 May be privileged. May be confidential. Please delete if not the addressee. _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
