On Thu, Oct 31, 2013 at 9:56 AM, Sandu Buraga <sandu.bur...@gmail.com>wrote:
> Hi, > > I am using SQLite 3.7.9, and QNX 6.5.0 running on Intel x86 machine. I am > having a use-case with multiple readers threads and one writer thread, all > running in the same process. No other process is using the SQLite database > file. > > I tried to enable WAL feature, but with no success so far. Each thread has > it's own handle: > > res = sqlite3_open_v2( m_FilePath.getBuffer(), &dbHandle, > > SQLITE_OPEN_READWRITE|SQLITE_OPEN_WAL|SQLITE_OPEN_FULLMUTEX|SQLITE_OPEN_PRIVATECACHE, > NULL ); > > immediately after I am making these PRAGMA statements for the new opened > handle > > "PRAGMA main.journal_mode=WAL;" > "PRAGMA temp_store=MEMORY;" > > So if I have 5 threads, I am calling the above sequence 5 times for each > distinct handle > (1) WAL mode is a persistent property of the database file. Set it once from a single-threaded connection and it will stay set forever. You should not try to set WAL mode on each connection separately. (2) WAL mode uses mmap() to get access to a small piece of memory that is shared between all connections. But the mmap() is unreliable on many version so QNX. If you must use WAL mode, first run "PRAGMA locking_mode=EXCLUSIVE". That will prevent all processes but the first from connecting to the database (though many threads from within that one process can have their own individual connections). And since only a single process is accessing the database, heap memory instead of mmap() memory is used for the shared memory region. This trick enables WAL mode to work reliably on QNX. > > When the code is executed I am getting frequently "databed locked" > messages. I tried to diagnose the issue, by enabling also the WAL traces in > the SQLite amalgamation, but I noticed no message, so for me it looks like > the WAL feature was not enabled. By analyzing the existed traces it looks > like thread 2 - reader is getting a SHARED lock, while later process 3 - > writer is trying to get an EXCLUSIVE lock. > > Any suggestion would be appreciated. > > Regards, > Sandu > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
