3.8. Obtaining An Exclusive Lock Prior to making changes to the database file itself, we must obtain an exclusive lock on the database file. Obtaining an exclusive lock is really a two-step process. First SQLite obtains a "pending" lock. Then it escalates the pending ... 

 ... When a connection using asynchronous IO begins a database transaction, the database is locked immediately. However the lock is not released until after all relevant operations in the write-queue have been flushed to disk. This means (for example) that ... 

2.3. Two processes using different locking protocols The default locking mechanism used by SQLite on unix platforms is POSIX advisory locking, but there are other options. By selecting an alternative sqlite3_vfs using the sqlite3_open_v2() interface, an application can make use of other locking protocols that might be ... 

sqlite3_wal_checkpoint_v2()

 ... The SQLITE_CHECKPOINT_FULL, RESTART and TRUNCATE modes also obtain the exclusive "writer" lock on the database file. If the writer lock cannot be obtained immediately, and a busy-handler is configured, it is invoked and the writer lock retried until either ... 

sqlite3_backup_init(), sqlite3_backup_step(), sqlite3_backup_finish(), sqlite3_backup_remaining(), sqlite3_backup_pagecount()

 ... The source database is read-locked only while it is being read; it is not locked continuously for the entire backup operation. Thus, the backup may be performed on a live source database without preventing other database connections from reading ... 

SQLITE_SHM_UNLOCK, SQLITE_SHM_LOCK, SQLITE_SHM_SHARED, SQLITE_SHM_EXCLUSIVE

These integer constants define the various locking operations allowed by the xShmLock method of sqlite3_io_methods. The following are the only legal combinations of flags to the xShmLock method: SQLITE_SHM_LOCK | SQLITE_SHM_SHARED SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE When unlocking, the same ... 

3.1. Standard Unix VFSes  ... unix-dotfile - uses dot-file locking rather than POSIX advisory locks. unix-excl - obtains and holds an exclusive lock on database files, preventing other processes from accessing the database. Also keeps the wal-index in heap rather than in shared ... 

 ... Establish a shared lock on the database file using the SQLite API (i.e. the shell tool). Copy the database file using an external tool (for example the unix 'cp' utility or the DOS 'copy' command). Relinquish the shared lock ... 

SQLITE_SHM_NLOCK

 ... The SQLite core will never attempt to acquire or release a lock outside of this range See also lists of Objects, Constants, and Functions.

 ... Potential uses for xFileControl() might be functions to enable blocking locks with timeouts, to change the locking strategy (for example to use dot-file locks), to inquire about the status of a lock, or to break stale locks. The SQLite ...