SQLITE_FCNTL_LOCKSTATE
,
SQLITE_FCNTL_GET_LOCKPROXYFILE
,
SQLITE_FCNTL_SET_LOCKPROXYFILE
,
SQLITE_FCNTL_LAST_ERRNO
,
SQLITE_FCNTL_SIZE_HINT
,
SQLITE_FCNTL_CHUNK_SIZE
,
SQLITE_FCNTL_FILE_POINTER
,
SQLITE_FCNTL_SYNC_OMITTED
,
SQLITE_FCNTL_WIN32_AV_RETRY
,
SQLITE_FCNTL_PERSIST_WAL
,
SQLITE_FCNTL_OVERWRITE
,
SQLITE_FCNTL_VFSNAME
,
SQLITE_FCNTL_POWERSAFE_OVERWRITE
,
SQLITE_FCNTL_PRAGMA
,
SQLITE_FCNTL_BUSYHANDLER
,
SQLITE_FCNTL_TEMPFILENAME
,
SQLITE_FCNTL_MMAP_SIZE
,
SQLITE_FCNTL_TRACE
,
SQLITE_FCNTL_HAS_MOVED
,
SQLITE_FCNTL_SYNC
,
SQLITE_FCNTL_COMMIT_PHASETWO
,
SQLITE_FCNTL_WIN32_SET_HANDLE
,
SQLITE_FCNTL_WAL_BLOCK
,
SQLITE_FCNTL_ZIPVFS
,
SQLITE_FCNTL_RBU
,
SQLITE_FCNTL_VFS_POINTER
,
SQLITE_FCNTL_JOURNAL_POINTER
,
SQLITE_FCNTL_WIN32_GET_HANDLE
,
SQLITE_FCNTL_PDB
,
SQLITE_FCNTL_BEGIN_ATOMIC_WRITE
,
SQLITE_FCNTL_COMMIT_ATOMIC_WRITE
,
SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE
,
SQLITE_FCNTL_LOCK_TIMEOUT
,
SQLITE_FCNTL_DATA_VERSION
—
Standard File Control Opcodes
#define SQLITE_FCNTL_LOCKSTATE
#define SQLITE_FCNTL_GET_LOCKPROXYFILE
#define SQLITE_FCNTL_SET_LOCKPROXYFILE
#define SQLITE_FCNTL_LAST_ERRNO
#define SQLITE_FCNTL_SIZE_HINT
#define SQLITE_FCNTL_CHUNK_SIZE
#define SQLITE_FCNTL_FILE_POINTER
#define SQLITE_FCNTL_SYNC_OMITTED
#define SQLITE_FCNTL_WIN32_AV_RETRY
#define SQLITE_FCNTL_PERSIST_WAL
#define SQLITE_FCNTL_OVERWRITE
#define SQLITE_FCNTL_VFSNAME
#define SQLITE_FCNTL_POWERSAFE_OVERWRITE
#define SQLITE_FCNTL_PRAGMA
#define SQLITE_FCNTL_BUSYHANDLER
#define SQLITE_FCNTL_TEMPFILENAME
#define SQLITE_FCNTL_MMAP_SIZE
#define SQLITE_FCNTL_TRACE
#define SQLITE_FCNTL_HAS_MOVED
#define SQLITE_FCNTL_SYNC
#define SQLITE_FCNTL_COMMIT_PHASETWO
#define SQLITE_FCNTL_WIN32_SET_HANDLE
#define SQLITE_FCNTL_WAL_BLOCK
#define SQLITE_FCNTL_ZIPVFS
#define SQLITE_FCNTL_RBU
#define SQLITE_FCNTL_VFS_POINTER
#define SQLITE_FCNTL_JOURNAL_POINTER
#define SQLITE_FCNTL_WIN32_GET_HANDLE
#define SQLITE_FCNTL_PDB
#define SQLITE_FCNTL_BEGIN_ATOMIC_WRITE
#define SQLITE_FCNTL_COMMIT_ATOMIC_WRITE
#define SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE
#define SQLITE_FCNTL_LOCK_TIMEOUT
#define SQLITE_FCNTL_DATA_VERSION
These integer constants are opcodes for the xFileControl method of the
sqlite3_io_methods object and for the sqlite3_file_control() interface.
- The SQLITE_FCNTL_LOCKSTATE opcode is used for debugging. This opcode
causes the xFileControl method to write the current state of the lock (one
of SQLITE_LOCK_NONE, SQLITE_LOCK_SHARED, SQLITE_LOCK_RESERVED,
SQLITE_LOCK_PENDING, or SQLITE_LOCK_EXCLUSIVE) into an integer that the
pArg argument points to. This capability is used during testing and is
only available when the SQLITE_TEST compile-time option is used.
- The SQLITE_FCNTL_SIZE_HINT opcode is used by SQLite to give the VFS layer
a hint of how large the database file will grow to be during the current
transaction. This hint is not guaranteed to be accurate but it is often
close. The underlying VFS might choose to preallocate database file space
based on this hint in order to help writes to the database file run
faster.
- The SQLITE_FCNTL_CHUNK_SIZE opcode is used to request that the VFS extends
and truncates the database file in chunks of a size specified by the user.
The fourth argument to sqlite3_file_control() should point to an integer
(type int) containing the new chunk-size to use for the nominated
database. Allocating database file space in large chunks (say 1MB at a
time), may reduce file-system fragmentation and improve performance on
some systems.
- The SQLITE_FCNTL_FILE_POINTER opcode is used to obtain a pointer to the
sqlite3_file object associated with a particular database connection. See
also SQLITE_FCNTL_JOURNAL_POINTER.
- The SQLITE_FCNTL_JOURNAL_POINTER opcode is used to obtain a pointer to the
sqlite3_file object associated with the journal file (either the rollback
journal or the write-ahead log) for a particular database connection. See
also SQLITE_FCNTL_FILE_POINTER.
- No longer in use.
- The SQLITE_FCNTL_SYNC opcode is generated internally by SQLite and sent to
the VFS immediately before the xSync method is invoked on a database file
descriptor. Or, if the xSync method is not invoked because the user has
configured SQLite with PRAGMA synchronous=OFF it is invoked in place of
the xSync method. In most cases, the pointer argument passed with this
file-control is NULL. However, if the database file is being synced as
part of a multi-database commit, the argument points to a nul-terminated
string containing the transactions master-journal file name. VFSes that do
not need this signal should silently ignore this opcode. Applications
should not call sqlite3_file_control() with this opcode as doing so may
disrupt the operation of the specialized VFSes that do require it.
- The SQLITE_FCNTL_COMMIT_PHASETWO opcode is generated internally by SQLite
and sent to the VFS after a transaction has been committed immediately but
before the database is unlocked. VFSes that do not need this signal should
silently ignore this opcode. Applications should not call
sqlite3_file_control() with this opcode as doing so may disrupt the
operation of the specialized VFSes that do require it.
- The SQLITE_FCNTL_WIN32_AV_RETRY opcode is used to configure automatic
retry counts and intervals for certain disk I/O operations for the windows
VFS in order to provide robustness in the presence of anti-virus programs.
By default, the windows VFS will retry file read, file write, and file
delete operations up to 10 times, with a delay of 25 milliseconds before
the first retry and with the delay increasing by an additional 25
milliseconds with each subsequent retry. This opcode allows these two
values (10 retries and 25 milliseconds of delay) to be adjusted. The
values are changed for all database connections within the same process.
The argument is a pointer to an array of two integers where the first
integer is the new retry count and the second integer is the delay. If
either integer is negative, then the setting is not changed but instead
the prior value of that setting is written into the array entry, allowing
the current retry settings to be interrogated. The zDbName parameter is
ignored.
- The SQLITE_FCNTL_PERSIST_WAL opcode is used to set or query the persistent
Write Ahead Log setting. By default, the auxiliary write ahead log (WAL
file) and shared memory files used for transaction control are
automatically deleted when the latest connection to the database closes.
Setting persistent WAL mode causes those files to persist after close.
Persisting the files is useful when other processes that do not have write
permission on the directory containing the database file want to read the
database file, as the WAL and shared memory files must exist in order for
the database to be readable. The fourth parameter to
sqlite3_file_control() for this opcode should be a pointer to an integer.
That integer is 0 to disable persistent WAL mode or 1 to enable persistent
WAL mode. If the integer is -1, then it is overwritten with the current
WAL persistence setting.
- The SQLITE_FCNTL_POWERSAFE_OVERWRITE opcode is used to set or query the
persistent "powersafe-overwrite" or "PSOW" setting.
The PSOW setting determines the SQLITE_IOCAP_POWERSAFE_OVERWRITE bit of
the xDeviceCharacteristics methods. The fourth parameter to
sqlite3_file_control() for this opcode should be a pointer to an integer.
That integer is 0 to disable zero-damage mode or 1 to enable zero-damage
mode. If the integer is -1, then it is overwritten with the current
zero-damage mode setting.
- The SQLITE_FCNTL_OVERWRITE opcode is invoked by SQLite after opening a
write transaction to indicate that, unless it is rolled back for some
reason, the entire database file will be overwritten by the current
transaction. This is used by VACUUM operations.
- The SQLITE_FCNTL_VFSNAME opcode can be used to obtain the names of all
VFSes in the VFS stack. The names are of all VFS shims and the final
bottom-level VFS are written into memory obtained from sqlite3_malloc()
and the result is stored in the char* variable that the fourth parameter
of sqlite3_file_control() points to. The caller is responsible for freeing
the memory when done. As with all file-control actions, there is no
guarantee that this will actually do anything. Callers should initialize
the char* variable to a NULL pointer in case this file-control is not
implemented. This file-control is intended for diagnostic use only.
- The SQLITE_FCNTL_VFS_POINTER opcode finds a pointer to the top-level VFSes
currently in use. The argument X in
sqlite3_file_control(db,SQLITE_FCNTL_VFS_POINTER,X) must be of type
"sqlite3_vfs **". This opcodes will set *X to a pointer to the
top-level VFS. When there are multiple VFS shims in the stack, this opcode
finds the upper-most shim only.
- Whenever a PRAGMA statement is parsed, an SQLITE_FCNTL_PRAGMA file control
is sent to the open sqlite3_file object corresponding to the database file
to which the pragma statement refers. The argument to the
SQLITE_FCNTL_PRAGMA file control is an array of pointers to strings
(char**) in which the second element of the array is the name of the
pragma and the third element is the argument to the pragma or NULL if the
pragma has no argument. The handler for an SQLITE_FCNTL_PRAGMA file
control can optionally make the first element of the char** argument point
to a string obtained from sqlite3_mprintf() or the equivalent and that
string will become the result of the pragma or the error message if the
pragma fails. If the SQLITE_FCNTL_PRAGMA file control returns
SQLITE_NOTFOUND, then normal PRAGMA processing continues. If the
SQLITE_FCNTL_PRAGMA file control returns SQLITE_OK, then the parser
assumes that the VFS has handled the PRAGMA itself and the parser
generates a no-op prepared statement if result string is NULL, or that
returns a copy of the result string if the string is non-NULL. If the
SQLITE_FCNTL_PRAGMA file control returns any result code other than
SQLITE_OK or SQLITE_NOTFOUND, that means that the VFS encountered an error
while handling the PRAGMA and the compilation of the PRAGMA fails with an
error. The SQLITE_FCNTL_PRAGMA file control occurs at the beginning of
pragma statement analysis and so it is able to override built-in PRAGMA
statements.
- The SQLITE_FCNTL_BUSYHANDLER file-control may be invoked by SQLite on the
database file handle shortly after it is opened in order to provide a
custom VFS with access to the connections busy-handler callback. The
argument is of type (void **) - an array of two (void *) values. The first
(void *) actually points to a function of type (int (*)(void *)). In order
to invoke the connections busy-handler, this function should be invoked
with the second (void *) in the array as the only argument. If it returns
non-zero, then the operation should be retried. If it returns zero, the
custom VFS should abandon the current operation.
- Application can invoke the SQLITE_FCNTL_TEMPFILENAME file-control to have
SQLite generate a temporary filename using the same algorithm that is
followed to generate temporary filenames for TEMP tables and other
internal uses. The argument should be a char** which will be filled with
the filename written into memory obtained from sqlite3_malloc(). The
caller should invoke sqlite3_free() on the result to avoid a memory
leak.
- The SQLITE_FCNTL_MMAP_SIZE file control is used to query or set the
maximum number of bytes that will be used for memory-mapped I/O. The
argument is a pointer to a value of type sqlite3_int64 that is an advisory
maximum number of bytes in the file to memory map. The pointer is
overwritten with the old value. The limit is not changed if the value
originally pointed to is negative, and so the current limit can be queried
by passing in a pointer to a negative number. This file-control is used
internally to implement PRAGMA mmap_size.
- The SQLITE_FCNTL_TRACE file control provides advisory information to the
VFS about what the higher layers of the SQLite stack are doing. This file
control is used by some VFS activity tracing shims. The argument is a
zero-terminated string. Higher layers in the SQLite stack may generate
instances of this file control if the SQLITE_USE_FCNTL_TRACE compile-time
option is enabled.
- The SQLITE_FCNTL_HAS_MOVED file control interprets its argument as a
pointer to an integer and it writes a boolean into that integer depending
on whether or not the file has been renamed, moved, or deleted since it
was first opened.
- The SQLITE_FCNTL_WIN32_GET_HANDLE opcode can be used to obtain the
underlying native file handle associated with a file handle. This file
control interprets its argument as a pointer to a native file handle and
writes the resulting value there.
- The SQLITE_FCNTL_WIN32_SET_HANDLE opcode is used for debugging. This
opcode causes the xFileControl method to swap the file handle with the one
pointed to by the pArg argument. This capability is used during testing
and only needs to be supported when SQLITE_TEST is defined.
- The SQLITE_FCNTL_WAL_BLOCK is a signal to the VFS layer that it might be
advantageous to block on the next WAL lock if the lock is not immediately
available. The WAL subsystem issues this signal during rare circumstances
in order to fix a problem with priority inversion. Applications should
<em>not</em> use this file-control.
- The SQLITE_FCNTL_ZIPVFS opcode is implemented by zipvfs only. All other
VFS should return SQLITE_NOTFOUND for this opcode.
- The SQLITE_FCNTL_RBU opcode is implemented by the special VFS used by the
RBU extension only. All other VFS should return SQLITE_NOTFOUND for this
opcode.
- If the SQLITE_FCNTL_BEGIN_ATOMIC_WRITE opcode returns SQLITE_OK, then the
file descriptor is placed in "batch write mode", which means all
subsequent write operations will be deferred and done atomically at the
next SQLITE_FCNTL_COMMIT_ATOMIC_WRITE. Systems that do not support batch
atomic writes will return SQLITE_NOTFOUND. Following a successful
SQLITE_FCNTL_BEGIN_ATOMIC_WRITE and prior to the closing
SQLITE_FCNTL_COMMIT_ATOMIC_WRITE or SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE,
SQLite will make no VFS interface calls on the same sqlite3_file file
descriptor except for calls to the xWrite method and the xFileControl
method with SQLITE_FCNTL_SIZE_HINT.
- The SQLITE_FCNTL_COMMIT_ATOMIC_WRITE opcode causes all write operations
since the previous successful call to SQLITE_FCNTL_BEGIN_ATOMIC_WRITE to
be performed atomically. This file control returns SQLITE_OK if and only
if the writes were all performed successfully and have been committed to
persistent storage. Regardless of whether or not it is successful, this
file control takes the file descriptor out of batch write mode so that all
subsequent write operations are independent. SQLite will never invoke
SQLITE_FCNTL_COMMIT_ATOMIC_WRITE without a prior successful call to
SQLITE_FCNTL_BEGIN_ATOMIC_WRITE.
- The SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE opcode causes all write operations
since the previous successful call to SQLITE_FCNTL_BEGIN_ATOMIC_WRITE to
be rolled back. This file control takes the file descriptor out of batch
write mode so that all subsequent write operations are independent. SQLite
will never invoke SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE without a prior
successful call to SQLITE_FCNTL_BEGIN_ATOMIC_WRITE.
- The SQLITE_FCNTL_LOCK_TIMEOUT opcode causes attempts to obtain a file lock
using the xLock or xShmLock methods of the VFS to wait for up to M
milliseconds before failing, where M is the single unsigned integer
parameter.
- The SQLITE_FCNTL_DATA_VERSION opcode is used to detect changes to a
database file. The argument is a pointer to a 32-bit unsigned integer. The
"data version" for the pager is written into the pointer. The
"data version" changes whenever any change occurs to the
corresponding database file, either through SQL statements on the same
database connection or through transactions committed by separate database
connections possibly in other processes. The sqlite3_total_changes()
interface can be used to find if any database on the connection has
changed, but that interface responds to changes on TEMP as well as MAIN
and does not provide a mechanism to detect changes to MAIN only. Also, the
sqlite3_total_changes() interface responds to internal changes only and
omits changes made by other database connections. The PRAGMA data_version
command provide a mechanism to detect changes to a single attached
database that occur due to other database connections, but omits changes
implemented by the database connection on which it is called. This file
control is the only mechanism to detect changes that happen either
internally or externally and that are associated with a particular
attached database.
sqlite3_file(3),
sqlite3_file_control(3),
sqlite3_malloc(3),
sqlite3_io_methods(3),
sqlite3_malloc(3),
sqlite3_mprintf(3),
sqlite3_total_changes(3),
sqlite3_vfs(3),
SQLITE_FCNTL_LOCKSTATE(3),
SQLITE_IOCAP_ATOMIC(3),
SQLITE_LOCK_NONE(3),
SQLITE_OK(3)