.Dd March 11, 2017
.Dt SQLITE3_SNAPSHOT_OPEN 3
.Os
.Sh NAME
.Nm sqlite3_snapshot_open
.Nd Start a read transaction on an historical snapshot
.Sh SYNOPSIS
.Ft int 
.Fo sqlite3_snapshot_open
.Fa "sqlite3 *db"
.Fa "const char *zSchema"
.Fa "sqlite3_snapshot *pSnapshot "
.Fc
.Sh DESCRIPTION
The sqlite3_snapshot_open(D,S,P) interface
starts a read transaction for schema S of database connection
D such that the read transaction refers to historical snapshot
P, rather than the most recent change to the database.
The sqlite3_snapshot_open() interface returns
SQLITE_OK on success or an appropriate error code if it fails.
.Pp
In order to succeed, a call to sqlite3_snapshot_open(D,S,P)
must be the first operation following the BEGIN that takes the
schema S out of autocommit mode.
In other words, schema S must not currently be in a transaction for
sqlite3_snapshot_open(D,S,P) to work, but
the database connection D must be out of autocommit mode.
A snapshot will fail to open if it has been overwritten by
a checkpoint.
A call to sqlite3_snapshot_open(D,S,P)
will fail if the database connection D does not know that the database
file for schema S is in WAL mode.
A database connection might not know that the database file is in WAL mode
if there has been no prior I/O on that database connection, or if the
database entered WAL mode after the most recent I/O on the
database connection.
(Hint: Run "PRAGMA application_id" against a newly
opened database connection in order to make it ready to use snapshots.)
.Pp
The sqlite3_snapshot_open() interface is only
available when the SQLITE_ENABLE_SNAPSHOT compile-time option is used.
.Sh SEE ALSO
.Xr sqlite3_get_autocommit 3 ,
.Xr sqlite3 3 ,
.Xr sqlite3_snapshot 3 ,
.Xr sqlite3_snapshot_open 3