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SQLITE3_WAL_CHECKPOINT_V2(3) Library Functions Manual
NAME
sqlite3_wal_checkpoint_v2 - Checkpoint a database
SYNOPSIS
int
sqlite3_wal_checkpoint_v2(sqlite3 *db, const char *zDb, int eMode,
int *pnLog, int *pnCkpt );
DESCRIPTION
The sqlite3_wal_checkpoint_v2(D,X,M,L,C) interface runs a checkpoint
operation on database X of database connection D in mode M. Status
information is written back into integers pointed to by L and C. The M
parameter must be a valid checkpoint mode:
SQLITE_CHECKPOINT_PASSIVECheckpoint as many frames as possible without
waiting for any database readers or writers to finish, then sync
the database file if all frames in the log were checkpointed.
The busy-handler callback is never invoked in the
SQLITE_CHECKPOINT_PASSIVE mode. On the other hand, passive mode
might leave the checkpoint unfinished if there are concurrent
readers or writers.
SQLITE_CHECKPOINT_FULLThis mode blocks (it invokes the busy-handler
callback)
until there is no database writer and all readers are reading
from the most recent database snapshot. It then checkpoints all
frames in the log file and syncs the database file. This mode
blocks new database writers while it is pending, but new database
readers are allowed to continue unimpeded.
SQLITE_CHECKPOINT_RESTARTThis mode works the same way as
SQLITE_CHECKPOINT_FULL
with the addition that after checkpointing the log file it blocks
(calls the busy-handler callback) until all readers are reading
from the database file only. This ensures that the next writer
will restart the log file from the beginning. Like
SQLITE_CHECKPOINT_FULL, this mode blocks new database writer
attempts while it is pending, but does not impede readers.
SQLITE_CHECKPOINT_TRUNCATEThis mode works the same way as
SQLITE_CHECKPOINT_RESTART
with the addition that it also truncates the log file to zero
bytes just prior to a successful return.
If pnLog is not NULL, then *pnLog is set to the total number of frames in
the log file or to -1 if the checkpoint could not run because of an error
or because the database is not in WAL mode. If pnCkpt is not NULL,then
*pnCkpt is set to the total number of checkpointed frames in the log file
(including any that were already checkpointed before the function was
called) or to -1 if the checkpoint could not run due to an error or
because the database is not in WAL mode. Note that upon successful
completion of an SQLITE_CHECKPOINT_TRUNCATE, the log file will have been
truncated to zero bytes and so both *pnLog and *pnCkpt will be set to
zero.
All calls obtain an exclusive "checkpoint" lock on the database file. If
any other process is running a checkpoint operation at the same time, the
lock cannot be obtained and SQLITE_BUSY is returned. Even if there is a
busy-handler configured, it will not be invoked in this case.
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 the busy-handler returns 0 or
the lock is successfully obtained. The busy-handler is also invoked
while waiting for database readers as described above. If the busy-
handler returns 0 before the writer lock is obtained or while waiting for
database readers, the checkpoint operation proceeds from that point in
the same way as SQLITE_CHECKPOINT_PASSIVE - checkpointing as many frames
as possible without blocking any further. SQLITE_BUSY is returned in
this case.
If parameter zDb is NULL or points to a zero length string, then the
specified operation is attempted on all WAL databases attached to
database connection db. In this case the values written to output
parameters *pnLog and *pnCkpt are undefined. If an SQLITE_BUSY error is
encountered when processing one or more of the attached WAL databases,
the operation is still attempted on any remaining attached databases and
SQLITE_BUSY is returned at the end. If any other error occurs while
processing an attached database, processing is abandoned and the error
code is returned to the caller immediately. If no error (SQLITE_BUSY or
otherwise) is encountered while processing the attached databases,
SQLITE_OK is returned.
If database zDb is the name of an attached database that is not in WAL
mode, SQLITE_OK is returned and both *pnLog and *pnCkpt set to -1. If
zDb is not NULL (or a zero length string) and is not the name of any
attached database, SQLITE_ERROR is returned to the caller.
Unless it returns SQLITE_MISUSE, the sqlite3_wal_checkpoint_v2()
interface sets the error information that is queried by sqlite3_errcode()
and sqlite3_errmsg().
The PRAGMA wal_checkpoint command can be used to invoke this interface
from SQL.
SEE ALSO
sqlite3_busy_handler(3), SQLITE_CHECKPOINT_PASSIVE(3), sqlite3(3),
sqlite3_busy_handler(3), sqlite3_errcode(3)
NetBSD 9.99 December 19, 2018 NetBSD 9.99