.Dd December 19, 2018
.Dt SQLITE3_WAL_HOOK 3
.Os
.Sh NAME
.Nm sqlite3_wal_hook
.Nd Write-Ahead Log Commit Hook
.Sh SYNOPSIS
.Ft void *
.Fo sqlite3_wal_hook
.Fa "sqlite3*"
.Fa "int(*)(void *,sqlite3*,const char*,int)"
.Fa "void* "
.Fc
.Sh DESCRIPTION
The sqlite3_wal_hook() function is used to register
a callback that is invoked each time data is committed to a database
in wal mode.
.Pp
The callback is invoked by SQLite after the commit has taken place
and the associated write-lock on the database released  , so the implementation
may read, write or checkpoint the database as required.
.Pp
The first parameter passed to the callback function when it is invoked
is a copy of the third parameter passed to sqlite3_wal_hook() when
registering the callback.
The second is a copy of the database handle.
The third parameter is the name of the database that was written to
- either "main" or the name of an ATTACH-ed database.
The fourth parameter is the number of pages currently in the write-ahead
log file, including those that were just committed.
.Pp
The callback function should normally return SQLITE_OK.
If an error code is returned, that error will propagate back up through
the SQLite code base to cause the statement that provoked the callback
to report an error, though the commit will have still occurred.
If the callback returns SQLITE_ROW or SQLITE_DONE,
or if it returns a value that does not correspond to any valid SQLite
error code, the results are undefined.
.Pp
A single database handle may have at most a single write-ahead log
callback registered at one time.
Calling sqlite3_wal_hook() replaces any previously
registered write-ahead log callback.
Note that the sqlite3_wal_autocheckpoint()
interface and the wal_autocheckpoint pragma
both invoke sqlite3_wal_hook() and will overwrite
any prior sqlite3_wal_hook() settings.
.Sh SEE ALSO
.Xr sqlite3_wal_autocheckpoint 3 ,
.Xr sqlite3_wal_hook 3 ,
.Xr SQLITE_OK 3