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Changes On Branch snapshot-get
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Changes In Branch snapshot-get Excluding Merge-Ins

This is equivalent to a diff from 901d0b8f to 843c15a5

2015-12-11
12:44
Add the experimental snapshot interface. Because it is experimental, it is subject to change or removal at a later date. (check-in: 9b124a5a user: drh tags: trunk)
03:27
Mention that the snapshot interfaces are only available if SQLite is compiled with SQLITE_ENABLE_SNAPSHOT. (Closed-Leaf check-in: 843c15a5 user: drh tags: snapshot-get)
03:20
Disable the snapshot test scripts if not compiled with SQLITE_ENABLE_SNAPSHOT. (check-in: 5fd008f0 user: drh tags: snapshot-get)
2015-12-09
16:26
Simplification of the DROP TRIGGER logic using sqlite3NestedParse() instead of hand-coded VDBE code. This is a manual cherry-pick of the key change from check-in [c80bbf14b365d]. (check-in: 8021b4c8 user: drh tags: trunk)
16:04
Merge unrelated fixes from trunk. (check-in: 362615b4 user: drh tags: snapshot-get)
08:13
Merge latest trunk with this branch. (check-in: dc236f11 user: dan tags: onepass-delete-or)
2015-12-08
16:58
Changes to avoid undefined behavior in memset() and memcpy() and in the comparisons of pointers from different allocations. All problems are found by analysis tools - none have been seen in the wild. (check-in: 901d0b8f user: drh tags: trunk)
16:08
Avoid doing comparisons with pointers that might have been previously been passed to realloc() and/or free(). (check-in: f20396ad user: drh tags: trunk)

Changes to src/main.c.

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    (void)SQLITE_MISUSE_BKPT;
    return -1;
  }
#endif
  pBt = sqlite3DbNameToBtree(db, zDbName);
  return pBt ? sqlite3BtreeIsReadonly(pBt) : -1;
}


























































































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    (void)SQLITE_MISUSE_BKPT;
    return -1;
  }
#endif
  pBt = sqlite3DbNameToBtree(db, zDbName);
  return pBt ? sqlite3BtreeIsReadonly(pBt) : -1;
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Obtain a snapshot handle for the snapshot of database zDb currently 
** being read by handle db.
*/
int sqlite3_snapshot_get(
  sqlite3 *db, 
  const char *zDb,
  sqlite3_snapshot **ppSnapshot
){
  int rc = SQLITE_ERROR;
#ifndef SQLITE_OMIT_WAL
  int iDb;

#ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
#endif
  sqlite3_mutex_enter(db->mutex);

  iDb = sqlite3FindDbName(db, zDb);
  if( iDb==0 || iDb>1 ){
    Btree *pBt = db->aDb[iDb].pBt;
    if( 0==sqlite3BtreeIsInTrans(pBt) ){
      rc = sqlite3BtreeBeginTrans(pBt, 0);
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerSnapshotGet(sqlite3BtreePager(pBt), ppSnapshot);
      }
    }
  }

  sqlite3_mutex_leave(db->mutex);
#endif   /* SQLITE_OMIT_WAL */
  return rc;
}

/*
** Open a read-transaction on the snapshot idendified by pSnapshot.
*/
int sqlite3_snapshot_open(
  sqlite3 *db, 
  const char *zDb, 
  sqlite3_snapshot *pSnapshot
){
  int rc = SQLITE_ERROR;
#ifndef SQLITE_OMIT_WAL

#ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) ){
    return SQLITE_MISUSE_BKPT;
  }
#endif
  sqlite3_mutex_enter(db->mutex);
  if( db->autoCommit==0 ){
    int iDb;
    iDb = sqlite3FindDbName(db, zDb);
    if( iDb==0 || iDb>1 ){
      Btree *pBt = db->aDb[iDb].pBt;
      if( 0==sqlite3BtreeIsInReadTrans(pBt) ){
        rc = sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), pSnapshot);
        if( rc==SQLITE_OK ){
          rc = sqlite3BtreeBeginTrans(pBt, 0);
          sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), 0);
        }
      }
    }
  }

  sqlite3_mutex_leave(db->mutex);
#endif   /* SQLITE_OMIT_WAL */
  return rc;
}

/*
** Free a snapshot handle obtained from sqlite3_snapshot_get().
*/
void sqlite3_snapshot_free(sqlite3_snapshot *pSnapshot){
  sqlite3_free(pSnapshot);
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

Changes to src/pager.c.

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      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}





























#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** A read-lock must be held on the pager when this function is called. If
** the pager is in WAL mode and the WAL file currently contains one or more
** frames, return the size in bytes of the page images stored within the







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      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** If this is a WAL database, obtain a snapshot handle for the snapshot
** currently open. Otherwise, return an error.
*/
int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot){
  int rc = SQLITE_ERROR;
  if( pPager->pWal ){
    rc = sqlite3WalSnapshotGet(pPager->pWal, ppSnapshot);
  }
  return rc;
}

/*
** If this is a WAL database, store a pointer to pSnapshot. Next time a
** read transaction is opened, attempt to read from the snapshot it 
** identifies. If this is not a WAL database, return an error.
*/
int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot){
  int rc = SQLITE_OK;
  if( pPager->pWal ){
    sqlite3WalSnapshotOpen(pPager->pWal, pSnapshot);
  }else{
    rc = SQLITE_ERROR;
  }
  return rc;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */
#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** A read-lock must be held on the pager when this function is called. If
** the pager is in WAL mode and the WAL file currently contains one or more
** frames, return the size in bytes of the page images stored within the

Changes to src/pager.h.

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#ifndef SQLITE_OMIT_WAL
  int sqlite3PagerCheckpoint(Pager *pPager, int, int*, int*);
  int sqlite3PagerWalSupported(Pager *pPager);
  int sqlite3PagerWalCallback(Pager *pPager);
  int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
  int sqlite3PagerCloseWal(Pager *pPager);




#endif

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */







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#ifndef SQLITE_OMIT_WAL
  int sqlite3PagerCheckpoint(Pager *pPager, int, int*, int*);
  int sqlite3PagerWalSupported(Pager *pPager);
  int sqlite3PagerWalCallback(Pager *pPager);
  int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
  int sqlite3PagerCloseWal(Pager *pPager);
# ifdef SQLITE_ENABLE_SNAPSHOT
  int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot);
  int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot);
# endif
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */

Changes to src/sqlite.h.in.

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** ^The sqlite3_value_dup(V) interface returns NULL if V is NULL or if a
** memory allocation fails.
**
** ^The sqlite3_value_free(V) interface frees an [sqlite3_value] object
** previously obtained from [sqlite3_value_dup()].  ^If V is a NULL pointer
** then sqlite3_value_free(V) is a harmless no-op.
*/
SQLITE_EXPERIMENTAL sqlite3_value *sqlite3_value_dup(const sqlite3_value*);
SQLITE_EXPERIMENTAL void sqlite3_value_free(sqlite3_value*);

/*
** CAPI3REF: Obtain Aggregate Function Context
** METHOD: sqlite3_context
**
** Implementations of aggregate SQL functions use this
** routine to allocate memory for storing their state.







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** ^The sqlite3_value_dup(V) interface returns NULL if V is NULL or if a
** memory allocation fails.
**
** ^The sqlite3_value_free(V) interface frees an [sqlite3_value] object
** previously obtained from [sqlite3_value_dup()].  ^If V is a NULL pointer
** then sqlite3_value_free(V) is a harmless no-op.
*/
sqlite3_value *sqlite3_value_dup(const sqlite3_value*);
void sqlite3_value_free(sqlite3_value*);

/*
** CAPI3REF: Obtain Aggregate Function Context
** METHOD: sqlite3_context
**
** Implementations of aggregate SQL functions use this
** routine to allocate memory for storing their state.
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** symbol [SQLITE_ENABLE_STMT_SCANSTATUS] defined.
*/
void sqlite3_stmt_scanstatus_reset(sqlite3_stmt*);

/*
** CAPI3REF: Flush caches to disk mid-transaction
**
** If a write-transaction is open when this function is called, any dirty

** pages in the pager-cache that are not currently in use are written out 
** to disk. A dirty page may be in use if a database cursor created by an
** active SQL statement is reading from it, or if it is page 1 of a database
** file (page 1 is always "in use"). Dirty pages are flushed for all
** databases - "main", "temp" and any attached databases.

**
** If this function needs to obtain extra database locks before dirty pages 
** can be flushed to disk, it does so. If said locks cannot be obtained 
** immediately and there is a busy-handler callback configured, it is invoked
** in the usual manner. If the required lock still cannot be obtained, then
** the database is skipped and an attempt made to flush any dirty pages
** belonging to the next (if any) database. If any databases are skipped
** because locks cannot be obtained, but no other error occurs, this
** function returns SQLITE_BUSY.
**
** If any other error occurs while flushing dirty pages to disk (for
** example an IO error or out-of-memory condition), then processing is
** abandoned and an SQLite error code returned to the caller immediately.
**
** Otherwise, if no error occurs, SQLITE_OK is returned.
**
** This function does not set the database handle error code or message
** returned by the sqlite3_errcode() and sqlite3_errmsg() functions.
*/
int sqlite3_db_cacheflush(sqlite3*);





























































































/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */







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** symbol [SQLITE_ENABLE_STMT_SCANSTATUS] defined.
*/
void sqlite3_stmt_scanstatus_reset(sqlite3_stmt*);

/*
** CAPI3REF: Flush caches to disk mid-transaction
**
** ^If a write-transaction is open on [database connection] D when the
** [sqlite3_db_cacheflush(D)] interface invoked, any dirty
** pages in the pager-cache that are not currently in use are written out 
** to disk. A dirty page may be in use if a database cursor created by an
** active SQL statement is reading from it, or if it is page 1 of a database
** file (page 1 is always "in use").  ^The [sqlite3_db_cacheflush(D)]
** interface flushes caches for all schemas - "main", "temp", and
** any [attached] databases.
**
** ^If this function needs to obtain extra database locks before dirty pages 
** can be flushed to disk, it does so. ^If those locks cannot be obtained 
** immediately and there is a busy-handler callback configured, it is invoked
** in the usual manner. ^If the required lock still cannot be obtained, then
** the database is skipped and an attempt made to flush any dirty pages
** belonging to the next (if any) database. ^If any databases are skipped
** because locks cannot be obtained, but no other error occurs, this
** function returns SQLITE_BUSY.
**
** ^If any other error occurs while flushing dirty pages to disk (for
** example an IO error or out-of-memory condition), then processing is
** abandoned and an SQLite [error code] is returned to the caller immediately.
**
** ^Otherwise, if no error occurs, [sqlite3_db_cacheflush()] returns SQLITE_OK.
**
** ^This function does not set the database handle error code or message
** returned by the [sqlite3_errcode()] and [sqlite3_errmsg()] functions.
*/
int sqlite3_db_cacheflush(sqlite3*);

/*
** CAPI3REF: Database Snapshot
** KEYWORDS: {snapshot}
** EXPERIMENTAL
**
** An instance of the snapshot object records the state of a [WAL mode]
** database for some specific point in history.
**
** In [WAL mode], multiple [database connections] that are open on the
** same database file can each be reading a different historical version
** of the database file.  When a [database connection] begins a read
** transaction, that connection sees an unchanging copy of the database
** as it existed for the point in time when the transaction first started.
** Subsequent changes to the database from other connections are not seen
** by the reader until a new read transaction is started.
**
** The sqlite3_snapshot object records state information about an historical
** version of the database file so that it is possible to later open a new read
** transaction that sees that historical version of the database rather than
** the most recent version.
**
** The constructor for this object is [sqlite3_snapshot_get()].  The
** [sqlite3_snapshot_open()] method causes a fresh read transaction to refer
** to an historical snapshot (if possible).  The destructor for 
** sqlite3_snapshot objects is [sqlite3_snapshot_free()].
*/
typedef struct sqlite3_snapshot sqlite3_snapshot;

/*
** CAPI3REF: Record A Database Snapshot
** EXPERIMENTAL
**
** ^The [sqlite3_snapshot_get(D,S,P)] interface attempts to make a
** new [sqlite3_snapshot] object that records the current state of
** schema S in database connection D.  ^On success, the
** [sqlite3_snapshot_get(D,S,P)] interface writes a pointer to the newly
** created [sqlite3_snapshot] object into *P and returns SQLITE_OK.
** ^If schema S of [database connection] D is not a [WAL mode] database
** that is in a read transaction, then [sqlite3_snapshot_get(D,S,P)]
** leaves the *P value unchanged and returns an appropriate [error code].
**
** The [sqlite3_snapshot] object returned from a successful call to
** [sqlite3_snapshot_get()] must be freed using [sqlite3_snapshot_free()]
** to avoid a memory leak.
**
** The [sqlite3_snapshot_get()] interface is only available when the
** SQLITE_ENABLE_SNAPSHOT compile-time option is used.
*/
SQLITE_EXPERIMENTAL int sqlite3_snapshot_get(
  sqlite3 *db,
  const char *zSchema,
  sqlite3_snapshot **ppSnapshot
);

/*
** CAPI3REF: Start a read transaction on an historical snapshot
** EXPERIMENTAL
**
** ^The [sqlite3_snapshot_open(D,S,P)] interface attempts to move the
** read transaction that is currently open on schema S of
** [database connection] D so that it refers to historical [snapshot] P.
** ^The [sqlite3_snapshot_open()] interface returns SQLITE_OK on success
** or an appropriate [error code] if it fails.
**
** ^In order to succeed, a call to [sqlite3_snapshot_open(D,S,P)] must be
** the first operation, apart from other sqlite3_snapshot_open() calls,
** following the [BEGIN] that starts a new read transaction.
** ^A [snapshot] will fail to open if it has been overwritten by a 
** [checkpoint].  
**
** The [sqlite3_snapshot_open()] interface is only available when the
** SQLITE_ENABLE_SNAPSHOT compile-time option is used.
*/
SQLITE_EXPERIMENTAL int sqlite3_snapshot_open(
  sqlite3 *db,
  const char *zSchema,
  sqlite3_snapshot *pSnapshot
);

/*
** CAPI3REF: Destroy a snapshot
** EXPERIMENTAL
**
** ^The [sqlite3_snapshot_free(P)] interface destroys [sqlite3_snapshot] P.
** The application must eventually free every [sqlite3_snapshot] object
** using this routine to avoid a memory leak.
**
** The [sqlite3_snapshot_free()] interface is only available when the
** SQLITE_ENABLE_SNAPSHOT compile-time option is used.
*/
SQLITE_EXPERIMENTAL void sqlite3_snapshot_free(sqlite3_snapshot*);

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif /* _SQLITE3_H_ */

Changes to src/test1.c.

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    return TCL_ERROR;
  }
  pVfs->xCurrentTimeInt64(pVfs, &t);
  Tcl_SetObjResult(interp, Tcl_NewWideIntObj(t));
  return TCL_OK;
}

























































































/*
** Usage:  sqlite3_next_stmt  DB  STMT
**
** Return the next statment in sequence after STMT.
*/
static int test_next_stmt(
  void * clientData,







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2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
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2329
2330
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2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
    return TCL_ERROR;
  }
  pVfs->xCurrentTimeInt64(pVfs, &t);
  Tcl_SetObjResult(interp, Tcl_NewWideIntObj(t));
  return TCL_OK;
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Usage: sqlite3_snapshot_get DB DBNAME
*/
static int test_snapshot_get(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  sqlite3 *db;
  char *zName;
  sqlite3_snapshot *pSnapshot = 0;

  if( objc!=3 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  zName = Tcl_GetString(objv[2]);

  rc = sqlite3_snapshot_get(db, zName, &pSnapshot);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }else{
    char zBuf[100];
    if( sqlite3TestMakePointerStr(interp, zBuf, pSnapshot) ) return TCL_ERROR;
    Tcl_SetObjResult(interp, Tcl_NewStringObj(zBuf, -1));
  }
  return TCL_OK;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Usage: sqlite3_snapshot_open DB DBNAME SNAPSHOT
*/
static int test_snapshot_open(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc;
  sqlite3 *db;
  char *zName;
  sqlite3_snapshot *pSnapshot;

  if( objc!=4 ){
    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME SNAPSHOT");
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
  zName = Tcl_GetString(objv[2]);
  pSnapshot = (sqlite3_snapshot*)sqlite3TestTextToPtr(Tcl_GetString(objv[3]));

  rc = sqlite3_snapshot_open(db, zName, pSnapshot);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }
  return TCL_OK;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

#ifdef SQLITE_ENABLE_SNAPSHOT
/*
** Usage: sqlite3_snapshot_free SNAPSHOT
*/
static int test_snapshot_free(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  sqlite3_snapshot *pSnapshot;
  if( objc!=2 ){
    Tcl_WrongNumArgs(interp, 1, objv, "SNAPSHOT");
    return TCL_ERROR;
  }
  pSnapshot = (sqlite3_snapshot*)sqlite3TestTextToPtr(Tcl_GetString(objv[1]));
  sqlite3_snapshot_free(pSnapshot);
  return TCL_OK;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

/*
** Usage:  sqlite3_next_stmt  DB  STMT
**
** Return the next statment in sequence after STMT.
*/
static int test_next_stmt(
  void * clientData,
7079
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7084
7085





7086
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7092
     { "sqlite3_stmt_scanstatus",       test_stmt_scanstatus,   0 },
     { "sqlite3_stmt_scanstatus_reset", test_stmt_scanstatus_reset,   0 },
#endif
#ifdef SQLITE_ENABLE_SQLLOG
     { "sqlite3_config_sqllog",         test_config_sqllog,   0 },
#endif
     { "vfs_current_time_int64",           vfsCurrentTimeInt64,   0 },





  };
  static int bitmask_size = sizeof(Bitmask)*8;
  static int longdouble_size = sizeof(LONGDOUBLE_TYPE);
  int i;
  extern int sqlite3_sync_count, sqlite3_fullsync_count;
  extern int sqlite3_opentemp_count;
  extern int sqlite3_like_count;







>
>
>
>
>







7167
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     { "sqlite3_stmt_scanstatus",       test_stmt_scanstatus,   0 },
     { "sqlite3_stmt_scanstatus_reset", test_stmt_scanstatus_reset,   0 },
#endif
#ifdef SQLITE_ENABLE_SQLLOG
     { "sqlite3_config_sqllog",         test_config_sqllog,   0 },
#endif
     { "vfs_current_time_int64",           vfsCurrentTimeInt64,   0 },
#ifdef SQLITE_ENABLE_SNAPSHOT
     { "sqlite3_snapshot_get", test_snapshot_get, 0 },
     { "sqlite3_snapshot_open", test_snapshot_open, 0 },
     { "sqlite3_snapshot_free", test_snapshot_free, 0 },
#endif
  };
  static int bitmask_size = sizeof(Bitmask)*8;
  static int longdouble_size = sizeof(LONGDOUBLE_TYPE);
  int i;
  extern int sqlite3_sync_count, sqlite3_fullsync_count;
  extern int sqlite3_opentemp_count;
  extern int sqlite3_like_count;

Changes to src/test_config.c.

138
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140
141
142
143
144






145
146
147
148
149
150
151
#endif

#ifdef SQLITE_ENABLE_MEMSYS5
  Tcl_SetVar2(interp, "sqlite_options", "mem5", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "mem5", "0", TCL_GLOBAL_ONLY);
#endif







#ifdef SQLITE_MUTEX_OMIT
  Tcl_SetVar2(interp, "sqlite_options", "mutex", "0", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "mutex", "1", TCL_GLOBAL_ONLY);
#endif








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>
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>
>
>







138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
#endif

#ifdef SQLITE_ENABLE_MEMSYS5
  Tcl_SetVar2(interp, "sqlite_options", "mem5", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "mem5", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_ENABLE_SNAPSHOT
  Tcl_SetVar2(interp, "sqlite_options", "snapshot", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "snapshot", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_MUTEX_OMIT
  Tcl_SetVar2(interp, "sqlite_options", "mutex", "0", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "mutex", "1", TCL_GLOBAL_ONLY);
#endif

Changes to src/wal.c.

268
269
270
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272
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274
275

276
277
278
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280
281
282
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284
285
286
287
288
289
290
291
292
293
294
295



296
297
298
299
300
301
302
** returns SQLITE_CANTOPEN.
*/
#define WAL_MAX_VERSION      3007000
#define WALINDEX_MAX_VERSION 3007000

/*
** Indices of various locking bytes.   WAL_NREADER is the number
** of available reader locks and should be at least 3.

*/
#define WAL_WRITE_LOCK         0
#define WAL_ALL_BUT_WRITE      1
#define WAL_CKPT_LOCK          1
#define WAL_RECOVER_LOCK       2
#define WAL_READ_LOCK(I)       (3+(I))
#define WAL_NREADER            (SQLITE_SHM_NLOCK-3)


/* Object declarations */
typedef struct WalIndexHdr WalIndexHdr;
typedef struct WalIterator WalIterator;
typedef struct WalCkptInfo WalCkptInfo;


/*
** The following object holds a copy of the wal-index header content.
**
** The actual header in the wal-index consists of two copies of this
** object.



**
** The szPage value can be any power of 2 between 512 and 32768, inclusive.
** Or it can be 1 to represent a 65536-byte page.  The latter case was
** added in 3.7.1 when support for 64K pages was added.  
*/
struct WalIndexHdr {
  u32 iVersion;                   /* Wal-index version */







|
>



















|
>
>
>







268
269
270
271
272
273
274
275
276
277
278
279
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286
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289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
** returns SQLITE_CANTOPEN.
*/
#define WAL_MAX_VERSION      3007000
#define WALINDEX_MAX_VERSION 3007000

/*
** Indices of various locking bytes.   WAL_NREADER is the number
** of available reader locks and should be at least 3.  The default
** is SQLITE_SHM_NLOCK==8 and  WAL_NREADER==5.
*/
#define WAL_WRITE_LOCK         0
#define WAL_ALL_BUT_WRITE      1
#define WAL_CKPT_LOCK          1
#define WAL_RECOVER_LOCK       2
#define WAL_READ_LOCK(I)       (3+(I))
#define WAL_NREADER            (SQLITE_SHM_NLOCK-3)


/* Object declarations */
typedef struct WalIndexHdr WalIndexHdr;
typedef struct WalIterator WalIterator;
typedef struct WalCkptInfo WalCkptInfo;


/*
** The following object holds a copy of the wal-index header content.
**
** The actual header in the wal-index consists of two copies of this
** object followed by one instance of the WalCkptInfo object.
** For all versions of SQLite through 3.10.0 and probably beyond,
** the locking bytes (WalCkptInfo.aLock) start at offset 120 and
** the total header size is 136 bytes.
**
** The szPage value can be any power of 2 between 512 and 32768, inclusive.
** Or it can be 1 to represent a 65536-byte page.  The latter case was
** added in 3.7.1 when support for 64K pages was added.  
*/
struct WalIndexHdr {
  u32 iVersion;                   /* Wal-index version */
320
321
322
323
324
325
326










327
328
329
330
331
332
333
** nBackfill is the number of frames in the WAL that have been written
** back into the database. (We call the act of moving content from WAL to
** database "backfilling".)  The nBackfill number is never greater than
** WalIndexHdr.mxFrame.  nBackfill can only be increased by threads
** holding the WAL_CKPT_LOCK lock (which includes a recovery thread).
** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from
** mxFrame back to zero when the WAL is reset.










**
** There is one entry in aReadMark[] for each reader lock.  If a reader
** holds read-lock K, then the value in aReadMark[K] is no greater than
** the mxFrame for that reader.  The value READMARK_NOT_USED (0xffffffff)
** for any aReadMark[] means that entry is unused.  aReadMark[0] is 
** a special case; its value is never used and it exists as a place-holder
** to avoid having to offset aReadMark[] indexs by one.  Readers holding







>
>
>
>
>
>
>
>
>
>







324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
** nBackfill is the number of frames in the WAL that have been written
** back into the database. (We call the act of moving content from WAL to
** database "backfilling".)  The nBackfill number is never greater than
** WalIndexHdr.mxFrame.  nBackfill can only be increased by threads
** holding the WAL_CKPT_LOCK lock (which includes a recovery thread).
** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from
** mxFrame back to zero when the WAL is reset.
**
** nBackfillAttempted is the largest value of nBackfill that a checkpoint
** has attempted to achieve.  Normally nBackfill==nBackfillAtempted, however
** the nBackfillAttempted is set before any backfilling is done and the
** nBackfill is only set after all backfilling completes.  So if a checkpoint
** crashes, nBackfillAttempted might be larger than nBackfill.  The
** WalIndexHdr.mxFrame must never be less than nBackfillAttempted.
**
** The aLock[] field is a set of bytes used for locking.  These bytes should
** never be read or written.
**
** There is one entry in aReadMark[] for each reader lock.  If a reader
** holds read-lock K, then the value in aReadMark[K] is no greater than
** the mxFrame for that reader.  The value READMARK_NOT_USED (0xffffffff)
** for any aReadMark[] means that entry is unused.  aReadMark[0] is 
** a special case; its value is never used and it exists as a place-holder
** to avoid having to offset aReadMark[] indexs by one.  Readers holding
360
361
362
363
364
365
366



367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
**
** We assume that 32-bit loads are atomic and so no locks are needed in
** order to read from any aReadMark[] entries.
*/
struct WalCkptInfo {
  u32 nBackfill;                  /* Number of WAL frames backfilled into DB */
  u32 aReadMark[WAL_NREADER];     /* Reader marks */



};
#define READMARK_NOT_USED  0xffffffff


/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems
** only support mandatory file-locks, we do not read or write data
** from the region of the file on which locks are applied.
*/
#define WALINDEX_LOCK_OFFSET   (sizeof(WalIndexHdr)*2 + sizeof(WalCkptInfo))
#define WALINDEX_LOCK_RESERVED 16
#define WALINDEX_HDR_SIZE      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)

/* Size of header before each frame in wal */
#define WAL_FRAME_HDRSIZE 24

/* Size of write ahead log header, including checksum. */
/* #define WAL_HDRSIZE 24 */
#define WAL_HDRSIZE 32







>
>
>









<
|
|







374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392

393
394
395
396
397
398
399
400
401
**
** We assume that 32-bit loads are atomic and so no locks are needed in
** order to read from any aReadMark[] entries.
*/
struct WalCkptInfo {
  u32 nBackfill;                  /* Number of WAL frames backfilled into DB */
  u32 aReadMark[WAL_NREADER];     /* Reader marks */
  u8 aLock[SQLITE_SHM_NLOCK];     /* Reserved space for locks */
  u32 nBackfillAttempted;         /* WAL frames perhaps written, or maybe not */
  u32 notUsed0;                   /* Available for future enhancements */
};
#define READMARK_NOT_USED  0xffffffff


/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems
** only support mandatory file-locks, we do not read or write data
** from the region of the file on which locks are applied.
*/

#define WALINDEX_LOCK_OFFSET (sizeof(WalIndexHdr)*2+offsetof(WalCkptInfo,aLock))
#define WALINDEX_HDR_SIZE    (sizeof(WalIndexHdr)*2+sizeof(WalCkptInfo))

/* Size of header before each frame in wal */
#define WAL_FRAME_HDRSIZE 24

/* Size of write ahead log header, including checksum. */
/* #define WAL_HDRSIZE 24 */
#define WAL_HDRSIZE 32
430
431
432
433
434
435
436



437
438
439
440
441
442
443
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  u32 minFrame;              /* Ignore wal frames before this one */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif



};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     







>
>
>







446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  u32 minFrame;              /* Ignore wal frames before this one */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
#ifdef SQLITE_ENABLE_SNAPSHOT
  WalIndexHdr *pSnapshot;    /* Start transaction here if not NULL */
#endif
};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     
1194
1195
1196
1197
1198
1199
1200

1201
1202
1203
1204
1205
1206
1207

    /* Reset the checkpoint-header. This is safe because this thread is 
    ** currently holding locks that exclude all other readers, writers and
    ** checkpointers.
    */
    pInfo = walCkptInfo(pWal);
    pInfo->nBackfill = 0;

    pInfo->aReadMark[0] = 0;
    for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
    if( pWal->hdr.mxFrame ) pInfo->aReadMark[1] = pWal->hdr.mxFrame;

    /* If more than one frame was recovered from the log file, report an
    ** event via sqlite3_log(). This is to help with identifying performance
    ** problems caused by applications routinely shutting down without







>







1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227

    /* Reset the checkpoint-header. This is safe because this thread is 
    ** currently holding locks that exclude all other readers, writers and
    ** checkpointers.
    */
    pInfo = walCkptInfo(pWal);
    pInfo->nBackfill = 0;
    pInfo->nBackfillAttempted = pWal->hdr.mxFrame;
    pInfo->aReadMark[0] = 0;
    for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
    if( pWal->hdr.mxFrame ) pInfo->aReadMark[1] = pWal->hdr.mxFrame;

    /* If more than one frame was recovered from the log file, report an
    ** event via sqlite3_log(). This is to help with identifying performance
    ** problems caused by applications routinely shutting down without
1265
1266
1267
1268
1269
1270
1271


1272


1273
1274
1275
1276
1277
1278
1279

  assert( zWalName && zWalName[0] );
  assert( pDbFd );

  /* In the amalgamation, the os_unix.c and os_win.c source files come before
  ** this source file.  Verify that the #defines of the locking byte offsets
  ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.


  */


#ifdef WIN_SHM_BASE
  assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
#ifdef UNIX_SHM_BASE
  assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif








>
>

>
>







1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303

  assert( zWalName && zWalName[0] );
  assert( pDbFd );

  /* In the amalgamation, the os_unix.c and os_win.c source files come before
  ** this source file.  Verify that the #defines of the locking byte offsets
  ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.
  ** For that matter, if the lock offset ever changes from its initial design
  ** value of 120, we need to know that so there is an assert() to check it.
  */
  assert( 120==WALINDEX_LOCK_OFFSET );
  assert( 136==WALINDEX_HDR_SIZE );
#ifdef WIN_SHM_BASE
  assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
#ifdef UNIX_SHM_BASE
  assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif

1651
1652
1653
1654
1655
1656
1657

1658
1659
1660
1661
1662
1663
1664
  u32 *aSalt = pWal->hdr.aSalt;   /* Big-endian salt values */
  pWal->nCkpt++;
  pWal->hdr.mxFrame = 0;
  sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
  memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
  walIndexWriteHdr(pWal);
  pInfo->nBackfill = 0;

  pInfo->aReadMark[1] = 0;
  for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
  assert( pInfo->aReadMark[0]==0 );
}

/*
** Copy as much content as we can from the WAL back into the database file







>







1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
  u32 *aSalt = pWal->hdr.aSalt;   /* Big-endian salt values */
  pWal->nCkpt++;
  pWal->hdr.mxFrame = 0;
  sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
  memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
  walIndexWriteHdr(pWal);
  pInfo->nBackfill = 0;
  pInfo->nBackfillAttempted = 0;
  pInfo->aReadMark[1] = 0;
  for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
  assert( pInfo->aReadMark[0]==0 );
}

/*
** Copy as much content as we can from the WAL back into the database file
1759
1760
1761
1762
1763
1764
1765


1766
1767
1768
1769
1770
1771
1772
    }

    if( pInfo->nBackfill<mxSafeFrame
     && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK
    ){
      i64 nSize;                    /* Current size of database file */
      u32 nBackfill = pInfo->nBackfill;



      /* Sync the WAL to disk */
      if( sync_flags ){
        rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
      }

      /* If the database may grow as a result of this checkpoint, hint







>
>







1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
    }

    if( pInfo->nBackfill<mxSafeFrame
     && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK
    ){
      i64 nSize;                    /* Current size of database file */
      u32 nBackfill = pInfo->nBackfill;

      pInfo->nBackfillAttempted = mxSafeFrame;

      /* Sync the WAL to disk */
      if( sync_flags ){
        rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
      }

      /* If the database may grow as a result of this checkpoint, hint
2143
2144
2145
2146
2147
2148
2149

2150
2151
2152
2153
2154
2155
2156
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
  volatile WalCkptInfo *pInfo;    /* Checkpoint information in wal-index */
  u32 mxReadMark;                 /* Largest aReadMark[] value */
  int mxI;                        /* Index of largest aReadMark[] value */
  int i;                          /* Loop counter */
  int rc = SQLITE_OK;             /* Return code  */


  assert( pWal->readLock<0 );     /* Not currently locked */

  /* Take steps to avoid spinning forever if there is a protocol error.
  **
  ** Circumstances that cause a RETRY should only last for the briefest
  ** instances of time.  No I/O or other system calls are done while the







>







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2182
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2184
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
  volatile WalCkptInfo *pInfo;    /* Checkpoint information in wal-index */
  u32 mxReadMark;                 /* Largest aReadMark[] value */
  int mxI;                        /* Index of largest aReadMark[] value */
  int i;                          /* Loop counter */
  int rc = SQLITE_OK;             /* Return code  */
  u32 mxFrame;                    /* Wal frame to lock to */

  assert( pWal->readLock<0 );     /* Not currently locked */

  /* Take steps to avoid spinning forever if there is a protocol error.
  **
  ** Circumstances that cause a RETRY should only last for the briefest
  ** instances of time.  No I/O or other system calls are done while the
2206
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2209
2210
2211
2212
2213





2214
2215
2216
2217
2218
2219
2220
    }
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){





    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    walShmBarrier(pWal);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){







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2234
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2252
2253
    }
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame 
#ifdef SQLITE_ENABLE_SNAPSHOT
   && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0
     || 0==memcmp(&pWal->hdr, pWal->pSnapshot, sizeof(WalIndexHdr)))
#endif
  ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    walShmBarrier(pWal);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
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2251
2252
2253
2254
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2301
2302
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  /* If we get this far, it means that the reader will want to use
  ** the WAL to get at content from recent commits.  The job now is
  ** to select one of the aReadMark[] entries that is closest to
  ** but not exceeding pWal->hdr.mxFrame and lock that entry.
  */
  mxReadMark = 0;
  mxI = 0;






  for(i=1; i<WAL_NREADER; i++){
    u32 thisMark = pInfo->aReadMark[i];
    if( mxReadMark<=thisMark && thisMark<=pWal->hdr.mxFrame ){
      assert( thisMark!=READMARK_NOT_USED );
      mxReadMark = thisMark;
      mxI = i;
    }
  }
  /* There was once an "if" here. The extra "{" is to preserve indentation. */
  {
    if( (pWal->readOnly & WAL_SHM_RDONLY)==0
     && (mxReadMark<pWal->hdr.mxFrame || mxI==0)
    ){
      for(i=1; i<WAL_NREADER; i++){
        rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame;
          mxI = i;
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
          break;
        }else if( rc!=SQLITE_BUSY ){
          return rc;
        }
      }
    }
    if( mxI==0 ){
      assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
      return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTLOCK;
    }

    rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
    if( rc ){
      return rc==SQLITE_BUSY ? WAL_RETRY : rc;
    }
    /* Now that the read-lock has been obtained, check that neither the
    ** value in the aReadMark[] array or the contents of the wal-index
    ** header have changed.
    **
    ** It is necessary to check that the wal-index header did not change
    ** between the time it was read and when the shared-lock was obtained
    ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
    ** that the log file may have been wrapped by a writer, or that frames
    ** that occur later in the log than pWal->hdr.mxFrame may have been
    ** copied into the database by a checkpointer. If either of these things
    ** happened, then reading the database with the current value of
    ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
    ** instead.
    **
    ** Before checking that the live wal-index header has not changed
    ** since it was read, set Wal.minFrame to the first frame in the wal
    ** file that has not yet been checkpointed. This client will not need
    ** to read any frames earlier than minFrame from the wal file - they
    ** can be safely read directly from the database file.
    **
    ** Because a ShmBarrier() call is made between taking the copy of 
    ** nBackfill and checking that the wal-header in shared-memory still
    ** matches the one cached in pWal->hdr, it is guaranteed that the 
    ** checkpointer that set nBackfill was not working with a wal-index
    ** header newer than that cached in pWal->hdr. If it were, that could
    ** cause a problem. The checkpointer could omit to checkpoint
    ** a version of page X that lies before pWal->minFrame (call that version
    ** A) on the basis that there is a newer version (version B) of the same
    ** page later in the wal file. But if version B happens to like past
    ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
    ** that it can read version A from the database file. However, since
    ** we can guarantee that the checkpointer that set nBackfill could not
    ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
    */
    pWal->minFrame = pInfo->nBackfill+1;
    walShmBarrier(pWal);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
      pWal->readLock = (i16)mxI;
    }
  }
  return rc;
}

/*
** Begin a read transaction on the database.
**







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2277
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2366
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2372
  /* If we get this far, it means that the reader will want to use
  ** the WAL to get at content from recent commits.  The job now is
  ** to select one of the aReadMark[] entries that is closest to
  ** but not exceeding pWal->hdr.mxFrame and lock that entry.
  */
  mxReadMark = 0;
  mxI = 0;
  mxFrame = pWal->hdr.mxFrame;
#ifdef SQLITE_ENABLE_SNAPSHOT
  if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){
    mxFrame = pWal->pSnapshot->mxFrame;
  }
#endif
  for(i=1; i<WAL_NREADER; i++){
    u32 thisMark = pInfo->aReadMark[i];
    if( mxReadMark<=thisMark && thisMark<=mxFrame ){
      assert( thisMark!=READMARK_NOT_USED );
      mxReadMark = thisMark;
      mxI = i;
    }
  }


  if( (pWal->readOnly & WAL_SHM_RDONLY)==0
   && (mxReadMark<mxFrame || mxI==0)
  ){
    for(i=1; i<WAL_NREADER; i++){
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        mxReadMark = pInfo->aReadMark[i] = mxFrame;
        mxI = i;
        walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
        break;
      }else if( rc!=SQLITE_BUSY ){
        return rc;
      }
    }
  }
  if( mxI==0 ){
    assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
    return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTLOCK;
  }

  rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
  if( rc ){
    return rc==SQLITE_BUSY ? WAL_RETRY : rc;
  }
  /* Now that the read-lock has been obtained, check that neither the
  ** value in the aReadMark[] array or the contents of the wal-index
  ** header have changed.
  **
  ** It is necessary to check that the wal-index header did not change
  ** between the time it was read and when the shared-lock was obtained
  ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
  ** that the log file may have been wrapped by a writer, or that frames
  ** that occur later in the log than pWal->hdr.mxFrame may have been
  ** copied into the database by a checkpointer. If either of these things
  ** happened, then reading the database with the current value of
  ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
  ** instead.
  **
  ** Before checking that the live wal-index header has not changed
  ** since it was read, set Wal.minFrame to the first frame in the wal
  ** file that has not yet been checkpointed. This client will not need
  ** to read any frames earlier than minFrame from the wal file - they
  ** can be safely read directly from the database file.
  **
  ** Because a ShmBarrier() call is made between taking the copy of 
  ** nBackfill and checking that the wal-header in shared-memory still
  ** matches the one cached in pWal->hdr, it is guaranteed that the 
  ** checkpointer that set nBackfill was not working with a wal-index
  ** header newer than that cached in pWal->hdr. If it were, that could
  ** cause a problem. The checkpointer could omit to checkpoint
  ** a version of page X that lies before pWal->minFrame (call that version
  ** A) on the basis that there is a newer version (version B) of the same
  ** page later in the wal file. But if version B happens to like past
  ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
  ** that it can read version A from the database file. However, since
  ** we can guarantee that the checkpointer that set nBackfill could not
  ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
  */
  pWal->minFrame = pInfo->nBackfill+1;
  walShmBarrier(pWal);
  if( pInfo->aReadMark[mxI]!=mxReadMark
   || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
  ){
    walUnlockShared(pWal, WAL_READ_LOCK(mxI));
    return WAL_RETRY;
  }else{
    assert( mxReadMark<=pWal->hdr.mxFrame );
    pWal->readLock = (i16)mxI;

  }
  return rc;
}

/*
** Begin a read transaction on the database.
**
2345
2346
2347
2348
2349
2350
2351








2352
2353
2354
2355
2356
2357
2358



























































2359
2360
2361
2362
2363
2364
2365
** Pager layer will use this to know that is cache is stale and
** needs to be flushed.
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int cnt = 0;                    /* Number of TryBeginRead attempts */









  do{
    rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
  }while( rc==WAL_RETRY );
  testcase( (rc&0xff)==SQLITE_BUSY );
  testcase( (rc&0xff)==SQLITE_IOERR );
  testcase( rc==SQLITE_PROTOCOL );
  testcase( rc==SQLITE_OK );



























































  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/







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2381
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2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
** Pager layer will use this to know that is cache is stale and
** needs to be flushed.
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int cnt = 0;                    /* Number of TryBeginRead attempts */

#ifdef SQLITE_ENABLE_SNAPSHOT
  int bChanged = 0;
  WalIndexHdr *pSnapshot = pWal->pSnapshot;
  if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
    bChanged = 1;
  }
#endif

  do{
    rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
  }while( rc==WAL_RETRY );
  testcase( (rc&0xff)==SQLITE_BUSY );
  testcase( (rc&0xff)==SQLITE_IOERR );
  testcase( rc==SQLITE_PROTOCOL );
  testcase( rc==SQLITE_OK );

#ifdef SQLITE_ENABLE_SNAPSHOT
  if( rc==SQLITE_OK ){
    if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
      /* At this point the client has a lock on an aReadMark[] slot holding
      ** a value equal to or smaller than pSnapshot->mxFrame, but pWal->hdr
      ** is populated with the wal-index header corresponding to the head
      ** of the wal file. Verify that pSnapshot is still valid before
      ** continuing.  Reasons why pSnapshot might no longer be valid:
      **
      **    (1)  The WAL file has been reset since the snapshot was taken.
      **         In this case, the salt will have changed.
      **
      **    (2)  A checkpoint as been attempted that wrote frames past
      **         pSnapshot->mxFrame into the database file.  Note that the
      **         checkpoint need not have completed for this to cause problems.
      */
      volatile WalCkptInfo *pInfo = walCkptInfo(pWal);

      assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 );
      assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame );

      /* It is possible that there is a checkpointer thread running 
      ** concurrent with this code. If this is the case, it may be that the
      ** checkpointer has already determined that it will checkpoint 
      ** snapshot X, where X is later in the wal file than pSnapshot, but 
      ** has not yet set the pInfo->nBackfillAttempted variable to indicate 
      ** its intent. To avoid the race condition this leads to, ensure that
      ** there is no checkpointer process by taking a shared CKPT lock 
      ** before checking pInfo->nBackfillAttempted.  */
      rc = walLockShared(pWal, WAL_CKPT_LOCK);

      if( rc==SQLITE_OK ){
        /* Check that the wal file has not been wrapped. Assuming that it has
        ** not, also check that no checkpointer has attempted to checkpoint any
        ** frames beyond pSnapshot->mxFrame. If either of these conditions are
        ** true, return SQLITE_BUSY_SNAPSHOT. Otherwise, overwrite pWal->hdr
        ** with *pSnapshot and set *pChanged as appropriate for opening the
        ** snapshot.  */
        if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
         && pSnapshot->mxFrame>=pInfo->nBackfillAttempted
        ){
          memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
          *pChanged = bChanged;
        }else{
          rc = SQLITE_BUSY_SNAPSHOT;
        }

        /* Release the shared CKPT lock obtained above. */
        walUnlockShared(pWal, WAL_CKPT_LOCK);
      }


      if( rc!=SQLITE_OK ){
        sqlite3WalEndReadTransaction(pWal);
      }
    }
  }
#endif
  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
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3162
3163
3164
3165
3166
3167





























3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal){
  return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}






























#ifdef SQLITE_ENABLE_ZIPVFS
/*
** If the argument is not NULL, it points to a Wal object that holds a
** read-lock. This function returns the database page-size if it is known,
** or zero if it is not (or if pWal is NULL).
*/
int sqlite3WalFramesize(Wal *pWal){
  assert( pWal==0 || pWal->readLock>=0 );
  return (pWal ? pWal->szPage : 0);
}
#endif

#endif /* #ifndef SQLITE_OMIT_WAL */







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3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
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3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal){
  return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}

#ifdef SQLITE_ENABLE_SNAPSHOT
/* Create a snapshot object.  The content of a snapshot is opaque to
** every other subsystem, so the WAL module can put whatever it needs
** in the object.
*/
int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){
  int rc = SQLITE_OK;
  WalIndexHdr *pRet;

  assert( pWal->readLock>=0 && pWal->writeLock==0 );

  pRet = (WalIndexHdr*)sqlite3_malloc(sizeof(WalIndexHdr));
  if( pRet==0 ){
    rc = SQLITE_NOMEM;
  }else{
    memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr));
    *ppSnapshot = (sqlite3_snapshot*)pRet;
  }

  return rc;
}

/* Try to open on pSnapshot when the next read-transaction starts
*/
void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){
  pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
}
#endif /* SQLITE_ENABLE_SNAPSHOT */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** If the argument is not NULL, it points to a Wal object that holds a
** read-lock. This function returns the database page-size if it is known,
** or zero if it is not (or if pWal is NULL).
*/
int sqlite3WalFramesize(Wal *pWal){
  assert( pWal==0 || pWal->readLock>=0 );
  return (pWal ? pWal->szPage : 0);
}
#endif

#endif /* #ifndef SQLITE_OMIT_WAL */

Changes to src/wal.h.

121
122
123
124
125
126
127





128
129
130
131
132
133
134
int sqlite3WalExclusiveMode(Wal *pWal, int op);

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);






#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif







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121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
int sqlite3WalExclusiveMode(Wal *pWal, int op);

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);

#ifdef SQLITE_ENABLE_SNAPSHOT
int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot);
void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot);
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
int sqlite3WalFramesize(Wal *pWal);
#endif

Added test/snapshot.test.









































































































































































































































































































































































































































































































































































































































































































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# 2015 December 7
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library. The focus
# of this file is the sqlite3_snapshot_xxx() APIs.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
ifcapable !snapshot {finish_test; return}
set testprefix snapshot

#-------------------------------------------------------------------------
# Check some error conditions in snapshot_get(). It is an error if:
#
#  1) snapshot_get() is called on a non-WAL database, or
#  2) there is an open write transaction on the database.
#
do_execsql_test 1.0 {
  CREATE TABLE t1(a, b);
  INSERT INTO t1 VALUES(1, 2);
  INSERT INTO t1 VALUES(3, 4);
}

do_test 1.1.1 {
  execsql { BEGIN; SELECT * FROM t1; }
  list [catch { sqlite3_snapshot_get db main } msg] $msg
} {1 SQLITE_ERROR}
do_execsql_test 1.1.2 COMMIT

do_test 1.2.1 {
  execsql {
    PRAGMA journal_mode = WAL;
    BEGIN;
      INSERT INTO t1 VALUES(5, 6);
      INSERT INTO t1 VALUES(7, 8);
  }
  list [catch { sqlite3_snapshot_get db main } msg] $msg
} {1 SQLITE_ERROR}
do_execsql_test 1.3.2 COMMIT

#-------------------------------------------------------------------------
# Check that a simple case works. Reuse the database created by the
# block of tests above.
#
do_execsql_test 2.1.0 {
  BEGIN;
    SELECT * FROM t1;
} {1 2 3 4 5 6 7 8}

breakpoint
do_test 2.1.1 {
  set snapshot [sqlite3_snapshot_get db main]
  execsql {
    COMMIT;
    INSERT INTO t1 VALUES(9, 10);
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6 7 8 9 10}

do_test 2.1.2 {
  execsql BEGIN
  sqlite3_snapshot_open db main $snapshot
  execsql {
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6 7 8}

do_test 2.1.3 {
  sqlite3_snapshot_free $snapshot
  execsql COMMIT
} {}

do_test 2.2.0 {
  sqlite3 db2 test.db
  execsql {
    BEGIN;
      SELECT * FROM t1;
  } db2
} {1 2 3 4 5 6 7 8 9 10}

do_test 2.2.1 {
  set snapshot [sqlite3_snapshot_get db2 main]
  execsql {
    INSERT INTO t1 VALUES(11, 12);
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6 7 8 9 10 11 12}

do_test 2.2.2 {
  execsql BEGIN
  sqlite3_snapshot_open db main $snapshot
  execsql {
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6 7 8 9 10}

do_test 2.2.3 {
  sqlite3_snapshot_free $snapshot
  execsql COMMIT
  execsql COMMIT db2
  db2 close
} {}

do_test 2.3.1 {
  execsql { DELETE FROM t1 WHERE a>6 }
  set snapshot [sqlite3_snapshot_get db main]
  execsql {
    INSERT INTO t1 VALUES('a', 'b');
    INSERT INTO t1 VALUES('c', 'd');
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6 a b c d}
do_test 2.3.2 {
  execsql BEGIN
  sqlite3_snapshot_open db main $snapshot
  execsql { SELECT * FROM t1 }
} {1 2 3 4 5 6}

do_test 2.3.3 {
  catchsql {
    INSERT INTO t1 VALUES('x','y')
  }
} {1 {database is locked}}
do_test 2.3.4 {
  execsql COMMIT
  sqlite3_snapshot_free $snapshot
} {}

#-------------------------------------------------------------------------
# Check some errors in sqlite3_snapshot_open(). It is an error if:
#
#   1) the db is in auto-commit mode,
#   2) the db has an open (read or write) transaction,
#   3) the db is not a wal database,
#
# Reuse the database created by earlier tests.
#
do_execsql_test 3.0.0 {
  CREATE TABLE t2(x, y);
  INSERT INTO t2 VALUES('a', 'b');
  INSERT INTO t2 VALUES('c', 'd');
  BEGIN;
    SELECT * FROM t2;
} {a b c d}
do_test 3.0.1 {
  set snapshot [sqlite3_snapshot_get db main]
  execsql { COMMIT }
  execsql { INSERT INTO t2 VALUES('e', 'f'); }
} {}

do_test 3.1 {
  list [catch {sqlite3_snapshot_open db main $snapshot } msg] $msg
} {1 SQLITE_ERROR}

do_test 3.2.1 {
  execsql {
    BEGIN;
      SELECT * FROM t2;
  }
} {a b c d e f}
do_test 3.2.2 {
  list [catch {sqlite3_snapshot_open db main $snapshot } msg] $msg
} {1 SQLITE_ERROR}

do_test 3.2.3 {
  execsql {
    COMMIT;
    BEGIN;
      INSERT INTO t2 VALUES('g', 'h');
  }
  list [catch {sqlite3_snapshot_open db main $snapshot } msg] $msg
} {1 SQLITE_ERROR}
do_execsql_test 3.2.4 COMMIT

do_test 3.3.1 {
  execsql { PRAGMA journal_mode = DELETE }
  execsql { BEGIN }
  list [catch {sqlite3_snapshot_open db main $snapshot } msg] $msg
} {1 SQLITE_ERROR}

do_test 3.3.2 {
  sqlite3_snapshot_free $snapshot
  execsql COMMIT
} {}

#-------------------------------------------------------------------------
# Check that SQLITE_BUSY_SNAPSHOT is returned if the specified snapshot
# no longer exists because the wal file has been checkpointed.
#
#   1. Reading a snapshot from the middle of a wal file is not possible
#      after the wal file has been checkpointed.
#
#   2. That a snapshot from the end of a wal file can not be read once
#      the wal file has been wrapped.
#
do_execsql_test 4.1.0 {
  PRAGMA journal_mode = wal;
  CREATE TABLE t3(i, j);
  INSERT INTO t3 VALUES('o', 't');
  INSERT INTO t3 VALUES('t', 'f');
  BEGIN;
    SELECT * FROM t3;
} {wal o t t f}

do_test 4.1.1 {
  set snapshot [sqlite3_snapshot_get db main]
  execsql COMMIT
} {}
do_test 4.1.2 {
  execsql { 
    INSERT INTO t3 VALUES('f', 's'); 
    BEGIN;
  }
  sqlite3_snapshot_open db main $snapshot
  execsql { SELECT * FROM t3 }
} {o t t f}

do_test 4.1.3 {
  execsql { 
    COMMIT;
    PRAGMA wal_checkpoint;
    BEGIN;
  }
  list [catch {sqlite3_snapshot_open db main $snapshot} msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}
do_test 4.1.4 {
  sqlite3_snapshot_free $snapshot
  execsql COMMIT
} {}

do_test 4.2.1 {
  execsql {
    INSERT INTO t3 VALUES('s', 'e');
    INSERT INTO t3 VALUES('n', 't');
    BEGIN;
      SELECT * FROM t3;
  }
} {o t t f f s s e n t}
do_test 4.2.2 {
  set snapshot [sqlite3_snapshot_get db main]
  execsql {
    COMMIT;
    PRAGMA wal_checkpoint;
    BEGIN;
  }
  sqlite3_snapshot_open db main $snapshot
  execsql { SELECT * FROM t3 }
} {o t t f f s s e n t}
do_test 4.2.3 {
  execsql {
    COMMIT;
    INSERT INTO t3 VALUES('e', 't');
    BEGIN;
  }
  list [catch {sqlite3_snapshot_open db main $snapshot} msg] $msg
} {1 SQLITE_BUSY_SNAPSHOT}
do_test 4.2.4 {
  sqlite3_snapshot_free $snapshot
} {}

#-------------------------------------------------------------------------
# Check that SQLITE_BUSY is returned if a checkpoint is running when
# sqlite3_snapshot_open() is called.
#
reset_db
db close
testvfs tvfs
sqlite3 db test.db -vfs tvfs

do_execsql_test 5.1 {
  PRAGMA journal_mode = wal;
  CREATE TABLE x1(x, xx, xxx);
  INSERT INTO x1 VALUES('z', 'zz', 'zzz');
  BEGIN;
    SELECT * FROM x1;
} {wal z zz zzz}

do_test 5.2 {
  set ::snapshot [sqlite3_snapshot_get db main]
  sqlite3 db2 test.db -vfs tvfs
  execsql {
    INSERT INTO x1 VALUES('a', 'aa', 'aaa');
    COMMIT;
  }
} {}

set t53 0
proc write_callback {args} {
  do_test 5.3.[incr ::t53] {
    execsql BEGIN
    list [catch { sqlite3_snapshot_open db main $::snapshot } msg] $msg
  } {1 SQLITE_BUSY}
  catchsql COMMIT
}

tvfs filter xWrite
tvfs script write_callback
db2 eval { PRAGMA wal_checkpoint }
db close
db2 close
tvfs delete
sqlite3_snapshot_free $snapshot

#-------------------------------------------------------------------------
# Test that sqlite3_snapshot_get() may be called immediately after
# "BEGIN; PRAGMA user_version;". And that sqlite3_snapshot_open() may
# be called after opening the db handle and running the script
# "PRAGMA user_version; BEGIN".
reset_db
do_execsql_test 6.1 {
  PRAGMA journal_mode = wal;
  CREATE TABLE x1(x, xx, xxx);
  INSERT INTO x1 VALUES('z', 'zz', 'zzz');
  BEGIN;
    PRAGMA user_version;
} {wal 0}
do_test 6.2 {
  set ::snapshot [sqlite3_snapshot_get db main]
  execsql {
    INSERT INTO x1 VALUES('a', 'aa', 'aaa');
    COMMIT;
  }
} {}
do_test 6.3 {
  sqlite3 db2 test.db 
  db2 eval "PRAGMA user_version ; BEGIN"
  sqlite3_snapshot_open db2 main $::snapshot
  db2 eval { SELECT * FROM x1 }
} {z zz zzz}
sqlite3_snapshot_free $snapshot

finish_test

Added test/snapshot_fault.test.









































































































































































































































































































































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# 2015 December 10
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library. The focus
# of this file is the sqlite3_snapshot_xxx() APIs.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
ifcapable !snapshot {finish_test; return}
set testprefix snapshot_fault

#-------------------------------------------------------------------------
# Check that an sqlite3_snapshot_open() client cannot be tricked into
# reading a corrupt snapshot even if a second client fails while 
# checkpointing the db.
#
do_faultsim_test 1.0 -prep {
  faultsim_delete_and_reopen
  sqlite3 db2 test.db
  db2 eval { 
    CREATE TABLE t1(a, b UNIQUE, c UNIQUE);
    INSERT INTO t1 VALUES(1, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(2, randomblob(500), randomblob(500));
    PRAGMA journal_mode = wal;
    INSERT INTO t1 VALUES(3, randomblob(500), randomblob(500));
    BEGIN;
      SELECT a FROM t1;
  }
  set ::snapshot [sqlite3_snapshot_get db2 main] 
  db2 eval COMMIT
  db2 eval {
    UPDATE t1 SET b=randomblob(501), c=randomblob(501) WHERE a=1;
    INSERT INTO t1 VALUES(4, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(5, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(6, randomblob(500), randomblob(500));
  }
} -body {
  db eval { PRAGMA wal_checkpoint }
} -test {
  db2 eval BEGIN
  if {[catch { sqlite3_snapshot_open db2 main $::snapshot } msg]} {
    if {$msg != "SQLITE_BUSY_SNAPSHOT" && $msg != "SQLITE_BUSY"} {
      error "error is $msg" 
    }
  } else {
    set res [db2 eval { 
      SELECT a FROM t1;
      PRAGMA integrity_check;
    }]
    if {$res != "1 2 3 ok"} { error "res is $res" }
  }

  sqlite3_snapshot_free $::snapshot
}

#-------------------------------------------------------------------------
# This test is similar to the previous one. Except, after the 
# "PRAGMA wal_checkpoint" command fails the db is closed and reopened
# so as to require wal file recovery. It should not be possible to open
# a snapshot that is part of the body of a recovered wal file.
#
do_faultsim_test 2.0 -prep {
  faultsim_delete_and_reopen
  db eval { 
    CREATE TABLE t1(a, b UNIQUE, c UNIQUE);
    INSERT INTO t1 VALUES(1, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(2, randomblob(500), randomblob(500));
    PRAGMA journal_mode = wal;
    INSERT INTO t1 VALUES(3, randomblob(500), randomblob(500));
    BEGIN;
      SELECT a FROM t1;
  }
  set ::snapshot [sqlite3_snapshot_get db main] 
  db eval COMMIT

  db eval {
    UPDATE t1 SET b=randomblob(501), c=randomblob(501) WHERE a=1;
    INSERT INTO t1 VALUES(4, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(5, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(6, randomblob(500), randomblob(500));
  }
} -body {
  db eval { PRAGMA wal_checkpoint }
} -test {

  db_save
  db close
  db_restore_and_reopen
  db eval { SELECT * FROM t1 }
  
  db eval BEGIN
  if {[catch { sqlite3_snapshot_open db main $::snapshot } msg]} {
    if {$msg != "SQLITE_BUSY_SNAPSHOT" && $msg != "SQLITE_BUSY"} {
      error "error is $msg" 
    }
  } else {
    # This branch should actually never be taken. But it was useful in
    # determining whether or not this test was actually working (by 
    # running a modified version of SQLite that allowed snapshots to be
    # opened following a recovery).
    error "TEST HAS FAILED"

    set res [db eval { 
      SELECT a FROM t1;
      PRAGMA integrity_check;
    }]
    if {$res != "1 2 3 ok"} { error "res is $res" }
  }

  sqlite3_snapshot_free $::snapshot
}

#-------------------------------------------------------------------------
# Test the handling of faults that occur within sqlite3_snapshot_open().
#
do_faultsim_test 3.0 -prep {
  faultsim_delete_and_reopen
  db eval { 
    CREATE TABLE t1(a, b UNIQUE, c UNIQUE);
    INSERT INTO t1 VALUES(1, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(2, randomblob(500), randomblob(500));
    PRAGMA journal_mode = wal;
    INSERT INTO t1 VALUES(3, randomblob(500), randomblob(500));
    BEGIN;
      SELECT a FROM t1;
  }
  set ::snapshot [sqlite3_snapshot_get db main] 
  db eval COMMIT
  db eval {
    UPDATE t1 SET b=randomblob(501), c=randomblob(501) WHERE a=1;
    INSERT INTO t1 VALUES(4, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(5, randomblob(500), randomblob(500));
    INSERT INTO t1 VALUES(6, randomblob(500), randomblob(500));
    BEGIN;
  }
} -body {
  if { [catch { sqlite3_snapshot_open db main $::snapshot } msg] } {
    error $msg
  }
} -test {
  faultsim_test_result {0 {}} {1 SQLITE_IOERR} \
                              {1 SQLITE_IOERR_NOMEM} {1 SQLITE_IOERR_READ}
  if {$testrc==0} {
    set res [db eval { 
      SELECT a FROM t1;
      PRAGMA integrity_check;
    }]
    if {$res != "1 2 3 ok"} { error "res is $res" }
  }

  sqlite3_snapshot_free $::snapshot
}



finish_test