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Overview
Comment:Updates to the documentation for sqlite3_wal_checkpoint_v2() and related interfaces, including adding many requirements marks.
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SHA1: 1e212d9899387344fd62c7b6fbcc59ea885b6d7c
User & Date: drh 2014-12-03 15:50:09
Context
2014-12-03
16:30
Futher tweaks to the sqlite3_wal_checkpoint_v2() documentation. check-in: 7d284d04 user: drh tags: trunk
15:50
Updates to the documentation for sqlite3_wal_checkpoint_v2() and related interfaces, including adding many requirements marks. check-in: 1e212d98 user: drh tags: trunk
2014-12-02
20:51
Add support for SQLITE_CHECKPOINT_TRUNCATE. check-in: edda2b9e user: drh tags: trunk
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Changes to src/sqlite.h.in.

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** on [database connection] D to be [checkpointed].  ^If X is NULL or an
** empty string, then a checkpoint is run on all databases of
** connection D.  ^If the database connection D is not in
** [WAL | write-ahead log mode] then this interface is a harmless no-op.
** ^The [sqlite3_wal_checkpoint(D,X)] interface initiates a
** [sqlite3_wal_checkpoint_v2|PASSIVE] checkpoint.
** Use the [sqlite3_wal_checkpoint_v2()] interface to get a FULL
** or RESET checkpoint.
**
** ^The [wal_checkpoint pragma] can be used to invoke this interface
** from SQL.  ^The [sqlite3_wal_autocheckpoint()] interface and the
** [wal_autocheckpoint pragma] can be used to cause this interface to be
** run whenever the WAL reaches a certain size threshold.
**
** See also: [sqlite3_wal_checkpoint_v2()]
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);

/*
** CAPI3REF: Checkpoint a database
**
** Run a checkpoint operation on WAL database zDb attached to database 
** handle db. The specific operation is determined by the value of the 
** eMode parameter:

**
** <dl>
** <dt>SQLITE_CHECKPOINT_PASSIVE<dd>
**   Checkpoint as many frames as possible without waiting for any database 
**   readers or writers to finish. Sync the db file if all frames in the log
**   are checkpointed. This mode is the same as calling 
**   sqlite3_wal_checkpoint(). The [sqlite3_busy_handler|busy-handler callback]
**   is never invoked.


**
** <dt>SQLITE_CHECKPOINT_FULL<dd>
**   This mode blocks (it invokes the
**   [sqlite3_busy_handler|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 call blocks database writers while it is running,
**   but not database readers.


**
** <dt>SQLITE_CHECKPOINT_RESTART<dd>
**   This mode works the same way as SQLITE_CHECKPOINT_FULL, except after 
**   checkpointing the log file it blocks (calls the 
**   [sqlite3_busy_handler|busy-handler callback])
**   until all readers are reading from the database file only. This ensures 
**   that the next client to write to the database file restarts the log file 
**   from the beginning. This call blocks database writers while it is running,
**   but not database readers.


**
** <dt>SQLITE_CHECKPOINT_TRUNCATE<dd>
**   This mode works the same way as SQLITE_CHECKPOINT_RESTART except that,
**   if successful, it also truncates the log file to zero bytes in size.

** </dl>
**
** If pnLog is not NULL, then *pnLog is set to the total number of frames in
** the log file before returning. If pnCkpt is not NULL, then *pnCkpt is set to

** the total number of checkpointed frames (including any that were already
** checkpointed when this function is called). *pnLog and *pnCkpt may be
** populated even if sqlite3_wal_checkpoint_v2() returns other than SQLITE_OK.
** If no values are available because of an error, they are both set to -1
** before returning to communicate this to the caller.



**
** 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. 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 to the caller. If any other 
** error occurs while processing an attached database, processing is abandoned 
** and the error code 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.



*/
int sqlite3_wal_checkpoint_v2(
  sqlite3 *db,                    /* Database handle */
  const char *zDb,                /* Name of attached database (or NULL) */
  int eMode,                      /* SQLITE_CHECKPOINT_* value */
  int *pnLog,                     /* OUT: Size of WAL log in frames */
  int *pnCkpt                     /* OUT: Total number of frames checkpointed */
);

/*
** CAPI3REF: Checkpoint operation parameters

**
** These constants can be used as the 3rd parameter to


** [sqlite3_wal_checkpoint_v2()].  See the [sqlite3_wal_checkpoint_v2()]
** documentation for additional information about the meaning and use of
** each of these values.

*/
#define SQLITE_CHECKPOINT_PASSIVE  0
#define SQLITE_CHECKPOINT_FULL     1
#define SQLITE_CHECKPOINT_RESTART  2
#define SQLITE_CHECKPOINT_TRUNCATE 3

/*
** CAPI3REF: Virtual Table Interface Configuration
**
** This function may be called by either the [xConnect] or [xCreate] method
** of a [virtual table] implementation to configure
** various facets of the virtual table interface.







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** on [database connection] D to be [checkpointed].  ^If X is NULL or an
** empty string, then a checkpoint is run on all databases of
** connection D.  ^If the database connection D is not in
** [WAL | write-ahead log mode] then this interface is a harmless no-op.
** ^The [sqlite3_wal_checkpoint(D,X)] interface initiates a
** [sqlite3_wal_checkpoint_v2|PASSIVE] checkpoint.
** Use the [sqlite3_wal_checkpoint_v2()] interface to get a FULL
** or RESET or TRUNCATE checkpoint.
**
** ^The [wal_checkpoint pragma] can be used to invoke this interface
** from SQL.  ^The [sqlite3_wal_autocheckpoint()] interface and the
** [wal_autocheckpoint pragma] can be used to cause this interface to be
** run whenever the WAL reaches a certain size threshold.
**
** See also: [sqlite3_wal_checkpoint_v2()]
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);

/*
** CAPI3REF: Checkpoint a database
**
** ^(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 [SQLITE_CHECKPOINT_PASSIVE|checkpoint mode]:)^
**
** <dl>
** <dt>SQLITE_CHECKPOINT_PASSIVE<dd>
**   ^Checkpoint 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. ^This mode is the same as calling 
**   [sqlite3_wal_checkpoint()]. ^The [sqlite3_busy_handler|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.
**
** <dt>SQLITE_CHECKPOINT_FULL<dd>
**   ^This mode blocks (it invokes the
**   [sqlite3_busy_handler|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.
**
** <dt>SQLITE_CHECKPOINT_RESTART<dd>
**   ^This mode works the same way as SQLITE_CHECKPOINT_FULL with the addition
**   that after checkpointing the log file it blocks (calls the 
**   [sqlite3_busy_handler|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.
**
** <dt>SQLITE_CHECKPOINT_TRUNCATE<dd>
**   ^This 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.
** </dl>
**
** ^If pnLog is not NULL, then *pnLog is set to the total number of frames in
** the log file before returning 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 (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.
**
** ^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.
**
** ^The [PRAGMA wal_checkpoint] command can be used to invoke this interface
** from SQL.
*/
int sqlite3_wal_checkpoint_v2(
  sqlite3 *db,                    /* Database handle */
  const char *zDb,                /* Name of attached database (or NULL) */
  int eMode,                      /* SQLITE_CHECKPOINT_* value */
  int *pnLog,                     /* OUT: Size of WAL log in frames */
  int *pnCkpt                     /* OUT: Total number of frames checkpointed */
);

/*
** CAPI3REF: Checkpoint Mode Values
** KEYWORDS: {checkpoint mode}
**

** These constants define all valid values for the "checkpoint mode" passed
** as the third parameter to the [sqlite3_wal_checkpoint_v2()] interface.
** See the [sqlite3_wal_checkpoint_v2()] documentation for details on the


** meaning of each of these checkpoint modes.
*/
#define SQLITE_CHECKPOINT_PASSIVE  0  /* Do as much as possible without blocking */
#define SQLITE_CHECKPOINT_FULL     1  /* Wait for writers to finish, then checkpoint */
#define SQLITE_CHECKPOINT_RESTART  2  /* Like FULL but afterwards block for readers */
#define SQLITE_CHECKPOINT_TRUNCATE 3  /* Like RESTART but also truncate the WAL file */

/*
** CAPI3REF: Virtual Table Interface Configuration
**
** This function may be called by either the [xConnect] or [xCreate] method
** of a [virtual table] implementation to configure
** various facets of the virtual table interface.