}
  }
}

#endif /* SQLITE_OMIT_SHARED_CACHE */


#ifdef SQLITE_ENABLE_CONCURRENT
/*
** The following structure - BtreePtrmap - stores the in-memory pointer map
** used for newly allocated pages in CONCURRENT transactions. Such pages are
** always allocated in a contiguous block (from the end of the file) starting
** with page BtreePtrmap.iFirst.
*/
typedef struct RollbackEntry RollbackEntry;
................................................................................
  int *aSvpt;                     /* First aRollback[] entry for savepoint i */

  int nRollback;                  /* Used size of aRollback[] array */
  int nRollbackAlloc;             /* Allocated size of aRollback[] array */
  RollbackEntry *aRollback;       /* Array of rollback entries */
};


/*
** If page number pgno is greater than or equal to BtreePtrmap.iFirst, 
** store an entry for it in the pointer-map structure.
*/
static int btreePtrmapStore(
  BtShared *pBt,
  Pgno pgno,
  u8 eType, 
................................................................................
    pMap->aPtr[iEntry].parent = parent;
    pMap->aPtr[iEntry].eType = eType;
  }

  return SQLITE_OK;
}


/*
** Open savepoint iSavepoint, if it is not already open.
*/
static int btreePtrmapBegin(BtShared *pBt, int nSvpt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap && nSvpt<pMap->nSvpt ){
    int i;
    if( nSvpt>=pMap->nSvptAlloc ){
................................................................................
    }
    pMap->nSvpt = nSvpt;
  }

  return SQLITE_OK;
}


/*
** Rollback (if op==SAVEPOINT_ROLLBACK) or release (if op==SAVEPOINT_RELEASE)
** savepoint iSvpt.
*/
static void btreePtrmapEnd(BtShared *pBt, int op, int iSvpt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap ){
    assert( op==SAVEPOINT_ROLLBACK || op==SAVEPOINT_RELEASE );
................................................................................
      }
      pMap->nSvpt = iSvpt + (op==SAVEPOINT_ROLLBACK);
      pMap->nRollback = pMap->aSvpt[iSvpt];
    }
  }
}


/*
** This function is called after an CONCURRENT transaction is opened on the
** database. It allocates the BtreePtrmap structure used to track pointers
** to allocated pages and zeroes the nFree/iTrunk fields in the database 
** header on page 1.
*/
static int btreePtrmapAllocate(BtShared *pBt){
  int rc = SQLITE_OK;
................................................................................
      pMap->iFirst = pBt->nPage + 1;
      pBt->pMap = pMap;
    }
  }
  return rc;
}


/*
** Free any BtreePtrmap structure allocated by an earlier call to
** btreePtrmapAllocate().
*/
static void btreePtrmapDelete(BtShared *pBt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap ){
    sqlite3_free(pMap->aRollback);
    sqlite3_free(pMap->aPtr);
    sqlite3_free(pMap->aSvpt);
    sqlite3_free(pMap);
    pBt->pMap = 0;
  }
}
#else
# define btreePtrmapAllocate(x) SQLITE_OK
# define btreePtrmapDelete(x) 
# define btreePtrmapBegin(x,y)  SQLITE_OK
# define btreePtrmapEnd(x,y,z) 
#endif

static void releasePage(MemPage *pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
................................................................................

  if( *pRC ) return;

  assert( sqlite3_mutex_held(pBt->mutex) );
  /* The master-journal page number is never added to a pointer-map page */
  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );

#ifdef SQLITE_ENABLE_CONCURRENT
  if( pBt->pMap ){
    *pRC = btreePtrmapStore(pBt, key, eType, parent);
    return;
  }
#endif

  assert( pBt->autoVacuum );
................................................................................
        }
      }
    }
  }


trans_begun:
#ifdef SQLITE_ENABLE_CONCURRENT
  if( bConcurrent && rc==SQLITE_OK && sqlite3PagerIsWal(pBt->pPager) ){
    rc = sqlite3PagerBeginConcurrent(pBt->pPager);
    if( rc==SQLITE_OK && wrflag ){
      rc = btreePtrmapAllocate(pBt);
    }
  }
#endif
................................................................................
  return rc;
}

#else /* ifndef SQLITE_OMIT_AUTOVACUUM */
# define setChildPtrmaps(x) SQLITE_OK
#endif

#ifdef SQLITE_ENABLE_CONCURRENT
/*
** This function is called as part of merging an CONCURRENT transaction with
** the snapshot at the head of the wal file. It relocates all pages in the
** range iFirst..iLast, inclusive. It is assumed that the BtreePtrmap 
** structure at BtShared.pMap contains the location of the pointers to each
** page in the range.
**
................................................................................
        releasePage(pPg);
      }
    }
  }
  return rc;
}


/*
** The b-tree handle passed as the only argument is about to commit an
** CONCURRENT transaction. At this point it is guaranteed that this is 
** possible - the wal WRITER lock is held and it is known that there are 
** no conflicts with committed transactions.
*/
static int btreeFixUnlocked(Btree *p){
  BtShared *pBt = p->pBt;
................................................................................
    sqlite3PagerSetDbsize(pPager, nFin);
  }

  return rc;
}
#else
# define btreeFixUnlocked(X)  SQLITE_OK
#endif /* ENABLE_CONCURRENT */

/*
** This routine does the first phase of a two-phase commit.  This routine
** causes a rollback journal to be created (if it does not already exist)
** and populated with enough information so that if a power loss occurs
** the database can be restored to its original state by playing back
** the journal.  Then the contents of the journal are flushed out to

    }
  }
}

#endif /* SQLITE_OMIT_SHARED_CACHE */


#ifndef SQLITE_OMIT_CONCURRENT
/*
** The following structure - BtreePtrmap - stores the in-memory pointer map
** used for newly allocated pages in CONCURRENT transactions. Such pages are
** always allocated in a contiguous block (from the end of the file) starting
** with page BtreePtrmap.iFirst.
*/
typedef struct RollbackEntry RollbackEntry;
................................................................................
  int *aSvpt;                     /* First aRollback[] entry for savepoint i */

  int nRollback;                  /* Used size of aRollback[] array */
  int nRollbackAlloc;             /* Allocated size of aRollback[] array */
  RollbackEntry *aRollback;       /* Array of rollback entries */
};

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** If page number pgno is greater than or equal to BtreePtrmap.iFirst, 
** store an entry for it in the pointer-map structure.
*/
static int btreePtrmapStore(
  BtShared *pBt,
  Pgno pgno,
  u8 eType, 
................................................................................
    pMap->aPtr[iEntry].parent = parent;
    pMap->aPtr[iEntry].eType = eType;
  }

  return SQLITE_OK;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Open savepoint iSavepoint, if it is not already open.
*/
static int btreePtrmapBegin(BtShared *pBt, int nSvpt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap && nSvpt<pMap->nSvpt ){
    int i;
    if( nSvpt>=pMap->nSvptAlloc ){
................................................................................
    }
    pMap->nSvpt = nSvpt;
  }

  return SQLITE_OK;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Rollback (if op==SAVEPOINT_ROLLBACK) or release (if op==SAVEPOINT_RELEASE)
** savepoint iSvpt.
*/
static void btreePtrmapEnd(BtShared *pBt, int op, int iSvpt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap ){
    assert( op==SAVEPOINT_ROLLBACK || op==SAVEPOINT_RELEASE );
................................................................................
      }
      pMap->nSvpt = iSvpt + (op==SAVEPOINT_ROLLBACK);
      pMap->nRollback = pMap->aSvpt[iSvpt];
    }
  }
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** This function is called after an CONCURRENT transaction is opened on the
** database. It allocates the BtreePtrmap structure used to track pointers
** to allocated pages and zeroes the nFree/iTrunk fields in the database 
** header on page 1.
*/
static int btreePtrmapAllocate(BtShared *pBt){
  int rc = SQLITE_OK;
................................................................................
      pMap->iFirst = pBt->nPage + 1;
      pBt->pMap = pMap;
    }
  }
  return rc;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Free any BtreePtrmap structure allocated by an earlier call to
** btreePtrmapAllocate().
*/
static void btreePtrmapDelete(BtShared *pBt){
  BtreePtrmap *pMap = pBt->pMap;
  if( pMap ){
    sqlite3_free(pMap->aRollback);
    sqlite3_free(pMap->aPtr);
    sqlite3_free(pMap->aSvpt);
    sqlite3_free(pMap);
    pBt->pMap = 0;
  }
}
#else  /* SQLITE_OMIT_CONCURRENT */
# define btreePtrmapAllocate(x) SQLITE_OK
# define btreePtrmapDelete(x) 
# define btreePtrmapBegin(x,y)  SQLITE_OK
# define btreePtrmapEnd(x,y,z) 
#endif /* SQLITE_OMIT_CONCURRENT */

static void releasePage(MemPage *pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
................................................................................

  if( *pRC ) return;

  assert( sqlite3_mutex_held(pBt->mutex) );
  /* The master-journal page number is never added to a pointer-map page */
  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );

#ifndef SQLITE_OMIT_CONCURRENT
  if( pBt->pMap ){
    *pRC = btreePtrmapStore(pBt, key, eType, parent);
    return;
  }
#endif

  assert( pBt->autoVacuum );
................................................................................
        }
      }
    }
  }


trans_begun:
#ifndef SQLITE_OMIT_CONCURRENT
  if( bConcurrent && rc==SQLITE_OK && sqlite3PagerIsWal(pBt->pPager) ){
    rc = sqlite3PagerBeginConcurrent(pBt->pPager);
    if( rc==SQLITE_OK && wrflag ){
      rc = btreePtrmapAllocate(pBt);
    }
  }
#endif
................................................................................
  return rc;
}

#else /* ifndef SQLITE_OMIT_AUTOVACUUM */
# define setChildPtrmaps(x) SQLITE_OK
#endif

#ifndef SQLITE_OMIT_CONCURRENT
/*
** This function is called as part of merging an CONCURRENT transaction with
** the snapshot at the head of the wal file. It relocates all pages in the
** range iFirst..iLast, inclusive. It is assumed that the BtreePtrmap 
** structure at BtShared.pMap contains the location of the pointers to each
** page in the range.
**
................................................................................
        releasePage(pPg);
      }
    }
  }
  return rc;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** The b-tree handle passed as the only argument is about to commit an
** CONCURRENT transaction. At this point it is guaranteed that this is 
** possible - the wal WRITER lock is held and it is known that there are 
** no conflicts with committed transactions.
*/
static int btreeFixUnlocked(Btree *p){
  BtShared *pBt = p->pBt;
................................................................................
    sqlite3PagerSetDbsize(pPager, nFin);
  }

  return rc;
}
#else
# define btreeFixUnlocked(X)  SQLITE_OK
#endif /* SQLITE_OMIT_CONCURRENT */

/*
** This routine does the first phase of a two-phase commit.  This routine
** causes a rollback journal to be created (if it does not already exist)
** and populated with enough information so that if a power loss occurs
** the database can be restored to its original state by playing back
** the journal.  Then the contents of the journal are flushed out to

#ifndef SQLITE_OMIT_SHARED_CACHE
  int nRef;             /* Number of references to this structure */
  BtShared *pNext;      /* Next on a list of sharable BtShared structs */
  BtLock *pLock;        /* List of locks held on this shared-btree struct */
  Btree *pWriter;       /* Btree with currently open write transaction */
#endif
  u8 *pTmpSpace;        /* Temp space sufficient to hold a single cell */
#ifdef SQLITE_ENABLE_CONCURRENT
  BtreePtrmap *pMap;
#endif
};

/*
** Allowed values for BtShared.btsFlags
*/
................................................................................
/*
** The ISAUTOVACUUM macro is used within balance_nonroot() to determine
** if the database supports auto-vacuum or not. Because it is used
** within an expression that is an argument to another macro 
** (sqliteMallocRaw), it is not possible to use conditional compilation.
** So, this macro is defined instead.
*/
#ifndef SQLITE_OMIT_AUTOVACUUM
#define ISAUTOVACUUM (pBt->autoVacuum)
#else
#define ISAUTOVACUUM 0
#endif

#ifdef SQLITE_ENABLE_CONCURRENT
# define ISCONCURRENT (pBt->pMap!=0)
#else
# define ISCONCURRENT 0
#endif

#define REQUIRE_PTRMAP (ISAUTOVACUUM || ISCONCURRENT)

/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.

#ifndef SQLITE_OMIT_SHARED_CACHE
  int nRef;             /* Number of references to this structure */
  BtShared *pNext;      /* Next on a list of sharable BtShared structs */
  BtLock *pLock;        /* List of locks held on this shared-btree struct */
  Btree *pWriter;       /* Btree with currently open write transaction */
#endif
  u8 *pTmpSpace;        /* Temp space sufficient to hold a single cell */
#ifndef SQLITE_OMIT_CONCURRENT
  BtreePtrmap *pMap;
#endif
};

/*
** Allowed values for BtShared.btsFlags
*/
................................................................................
/*
** The ISAUTOVACUUM macro is used within balance_nonroot() to determine
** if the database supports auto-vacuum or not. Because it is used
** within an expression that is an argument to another macro 
** (sqliteMallocRaw), it is not possible to use conditional compilation.
** So, this macro is defined instead.
*/
#ifdef SQLITE_OMIT_AUTOVACUUM
#define ISAUTOVACUUM 0
#else
#define ISAUTOVACUUM (pBt->autoVacuum)
#endif

#ifdef SQLITE_OMIT_CONCURRENT
# define ISCONCURRENT 0
#else
# define ISCONCURRENT (pBt->pMap!=0)
#endif

#define REQUIRE_PTRMAP (ISAUTOVACUUM || ISCONCURRENT)

/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.

  Pgno dbFileSize;            /* Number of pages in the database file */
  Pgno dbHintSize;            /* Value passed to FCNTL_SIZE_HINT call */
  int errCode;                /* One of several kinds of errors */
  int nRec;                   /* Pages journalled since last j-header written */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  u32 nSubRec;                /* Number of records written to sub-journal */
  Bitvec *pInJournal;         /* One bit for each page in the database file */
#ifdef SQLITE_ENABLE_CONCURRENT
  Bitvec *pAllRead;           /* Pages read within current CONCURRENT trans. */
#endif
  sqlite3_file *fd;           /* File descriptor for database */
  sqlite3_file *jfd;          /* File descriptor for main journal */
  sqlite3_file *sjfd;         /* File descriptor for sub-journal */
  i64 journalOff;             /* Current write offset in the journal file */
  i64 journalHdr;             /* Byte offset to previous journal header */
................................................................................

    case PAGER_WRITER_LOCKED:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
#ifdef SQLITE_ENABLE_CONCURRENT
      assert( pPager->dbSize==pPager->dbOrigSize || pPager->pAllRead );
#endif
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      assert( pPager->setMaster==0 );
      break;

................................................................................
      testcase( rc==SQLITE_NOMEM );
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

#ifdef SQLITE_ENABLE_CONCURRENT
/*
** If they are not already, begin recording all pages read from the pager layer
** by the b-tree layer This is used by concurrent transactions. Return
** SQLITE_OK if successful, or an SQLite error code (SQLITE_NOMEM) if an error
** occurs.
*/
int sqlite3PagerBeginConcurrent(Pager *pPager){
................................................................................
    if( pPager->pAllRead==0 ){
      rc = SQLITE_NOMEM;
    }
  }
  return rc;
}


/*
** Stop recording all pages read from the pager layer by the b-tree layer
** and discard any current records.
*/
void sqlite3PagerEndConcurrent(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pAllRead);
  pPager->pAllRead = 0;
}


/*
** Return true if the database is in wal mode. False otherwise.
*/
int sqlite3PagerIsWal(Pager *pPager){
  return pPager->pWal!=0;
}
#endif

/*
** Free the Pager.pInJournal and Pager.pAllRead bitvec objects.
*/
static void pagerFreeBitvecs(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
................................................................................
  **   + Discard the cached page (if refcount==0), or
  **   + Reload page content from the database (if refcount>0).
  */
  pPager->dbSize = pPager->dbOrigSize;
  rc = sqlite3WalUndo(pPager->pWal, pagerUndoCallback, (void *)pPager);
  pList = sqlite3PcacheDirtyList(pPager->pPCache);


  /* If this is an CONCURRENT transaction, then page 1 must be reread from 
  ** the db file, even if it is not dirty. This is because the b-tree layer 
  ** may have already zeroed the nFree and iTrunk header fields.  */
#ifdef SQLITE_ENABLE_CONCURRENT
  if( rc==SQLITE_OK && (pList==0 || pList->pgno!=1) && pPager->pAllRead ){
    rc = pagerUndoCallback((void*)pPager, 1);
  }
#endif

  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;
................................................................................
      || (pPg->flags & PGHDR_NEED_SYNC)!=0)
  ){
    return SQLITE_OK;
  }

  pPg->pDirty = 0;
  if( pagerUseWal(pPager) ){

    /* If the transaction is a "BEGIN CONCURRENT" transaction, the page 
    ** cannot be flushed to disk. Return early in this case. */
#ifdef SQLITE_ENABLE_CONCURRENT
    if( pPager->pAllRead ) return SQLITE_OK;
#endif

    /* Write a single frame for this page to the log. */
    rc = subjournalPageIfRequired(pPg); 
    if( rc==SQLITE_OK ){
      rc = pagerWalFrames(pPager, pPg, 0, 0);
................................................................................
  assert( noContent==0 || bMmapOk==0 );

  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  pPager->hasBeenUsed = 1;


  /* If this is an CONCURRENT transaction and the page being read was
  ** present in the database file when the transaction was opened,
  ** mark it as read in the pAllRead vector.  */
#ifdef SQLITE_ENABLE_CONCURRENT
  if( pPager->pAllRead && pgno<=pPager->dbOrigSize ){
    rc = sqlite3BitvecSet(pPager->pAllRead, pgno);
    if( rc!=SQLITE_OK ) goto pager_acquire_err;
  }
#endif

  /* If the pager is in the error state, return an error immediately. 
................................................................................
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
#if defined(SQLITE_ENABLE_CONCURRENT) || !defined(NDEBUG)
int sqlite3PagerIswriteable(DbPage *pPg){
  return pPg->flags & PGHDR_WRITEABLE;
}
#endif

/*
** A call to this routine tells the pager that it is not necessary to
................................................................................
       || pPager->eState==PAGER_WRITER_DBMOD 
       || pPager->eState==PAGER_WRITER_LOCKED 
  );
  assert( assert_pager_state(pPager) );
  if( 0==pagerUseWal(pPager) ){
    rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
  }
#ifdef SQLITE_ENABLE_CONCURRENT
  else{
    if( pPager->pAllRead ){
      /* This is an CONCURRENT transaction. Attempt to lock the wal database
      ** here. If SQLITE_BUSY (but not SQLITE_BUSY_SNAPSHOT) is returned,
      ** invoke the busy-handler and try again for as long as it returns
      ** non-zero.  */
      do {
        rc = sqlite3WalLockForCommit(pPager->pWal, pPage1, pPager->pAllRead);
      }while( rc==SQLITE_BUSY 
           && pPager->xBusyHandler(pPager->pBusyHandlerArg) 
      );
    }
  }
#endif
  return rc;
}

#ifdef SQLITE_ENABLE_CONCURRENT
/*
** This function is called as part of committing an CONCURRENT transaction.
** At this point the wal WRITER lock is held, and all pages in the cache 
** except for page 1 are compatible with the snapshot at the head of the
** wal file. 
**
** This function updates the in-memory data structures and reloads the
................................................................................
  if( rc==SQLITE_OK ){
    rc = readDbPage(pPage1, iFrame);
  }

  return rc;
}


/*
** Set the in-memory cache of the database file size to nSz pages.
*/
void sqlite3PagerSetDbsize(Pager *pPager, Pgno nSz){
  pPager->dbSize = nSz;
}


/*
** If this is a WAL mode connection and the WRITER lock is currently held,
** relinquish it.
*/
void sqlite3PagerDropExclusiveLock(Pager *pPager){
  if( pagerUseWal(pPager) ){
    sqlite3WalEndWriteTransaction(pPager->pWal);
  }
}
#endif   /* ifdef SQLITE_ENABLE_CONCURRENT */


/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
** journal file. zMaster may be NULL, which is interpreted as no master
** journal (a single database transaction).

  Pgno dbFileSize;            /* Number of pages in the database file */
  Pgno dbHintSize;            /* Value passed to FCNTL_SIZE_HINT call */
  int errCode;                /* One of several kinds of errors */
  int nRec;                   /* Pages journalled since last j-header written */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  u32 nSubRec;                /* Number of records written to sub-journal */
  Bitvec *pInJournal;         /* One bit for each page in the database file */
#ifndef SQLITE_OMIT_CONCURRENT
  Bitvec *pAllRead;           /* Pages read within current CONCURRENT trans. */
#endif
  sqlite3_file *fd;           /* File descriptor for database */
  sqlite3_file *jfd;          /* File descriptor for main journal */
  sqlite3_file *sjfd;         /* File descriptor for sub-journal */
  i64 journalOff;             /* Current write offset in the journal file */
  i64 journalHdr;             /* Byte offset to previous journal header */
................................................................................

    case PAGER_WRITER_LOCKED:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
#ifndef SQLITE_OMIT_CONCURRENT
      assert( pPager->dbSize==pPager->dbOrigSize || pPager->pAllRead );
#endif
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      assert( pPager->setMaster==0 );
      break;

................................................................................
      testcase( rc==SQLITE_NOMEM );
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

#ifndef SQLITE_OMIT_CONCURRENT
/*
** If they are not already, begin recording all pages read from the pager layer
** by the b-tree layer This is used by concurrent transactions. Return
** SQLITE_OK if successful, or an SQLite error code (SQLITE_NOMEM) if an error
** occurs.
*/
int sqlite3PagerBeginConcurrent(Pager *pPager){
................................................................................
    if( pPager->pAllRead==0 ){
      rc = SQLITE_NOMEM;
    }
  }
  return rc;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Stop recording all pages read from the pager layer by the b-tree layer
** and discard any current records.
*/
void sqlite3PagerEndConcurrent(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pAllRead);
  pPager->pAllRead = 0;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Return true if the database is in wal mode. False otherwise.
*/
int sqlite3PagerIsWal(Pager *pPager){
  return pPager->pWal!=0;
}
#endif /* SQLITE_OMIT_CONCURRENT */

/*
** Free the Pager.pInJournal and Pager.pAllRead bitvec objects.
*/
static void pagerFreeBitvecs(Pager *pPager){
  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
................................................................................
  **   + Discard the cached page (if refcount==0), or
  **   + Reload page content from the database (if refcount>0).
  */
  pPager->dbSize = pPager->dbOrigSize;
  rc = sqlite3WalUndo(pPager->pWal, pagerUndoCallback, (void *)pPager);
  pList = sqlite3PcacheDirtyList(pPager->pPCache);

#ifndef SQLITE_OMIT_CONCURRENT
  /* If this is an CONCURRENT transaction, then page 1 must be reread from 
  ** the db file, even if it is not dirty. This is because the b-tree layer 
  ** may have already zeroed the nFree and iTrunk header fields.  */

  if( rc==SQLITE_OK && (pList==0 || pList->pgno!=1) && pPager->pAllRead ){
    rc = pagerUndoCallback((void*)pPager, 1);
  }
#endif

  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;
................................................................................
      || (pPg->flags & PGHDR_NEED_SYNC)!=0)
  ){
    return SQLITE_OK;
  }

  pPg->pDirty = 0;
  if( pagerUseWal(pPager) ){
#ifndef SQLITE_OMIT_CONCURRENT
    /* If the transaction is a "BEGIN CONCURRENT" transaction, the page 
    ** cannot be flushed to disk. Return early in this case. */

    if( pPager->pAllRead ) return SQLITE_OK;
#endif

    /* Write a single frame for this page to the log. */
    rc = subjournalPageIfRequired(pPg); 
    if( rc==SQLITE_OK ){
      rc = pagerWalFrames(pPager, pPg, 0, 0);
................................................................................
  assert( noContent==0 || bMmapOk==0 );

  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  pPager->hasBeenUsed = 1;

#ifndef SQLITE_OMIT_CONCURRENT
  /* If this is an CONCURRENT transaction and the page being read was
  ** present in the database file when the transaction was opened,
  ** mark it as read in the pAllRead vector.  */

  if( pPager->pAllRead && pgno<=pPager->dbOrigSize ){
    rc = sqlite3BitvecSet(pPager->pAllRead, pgno);
    if( rc!=SQLITE_OK ) goto pager_acquire_err;
  }
#endif

  /* If the pager is in the error state, return an error immediately. 
................................................................................
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
#if !defined(SQLITE_OMIT_CONCURRENT) || !defined(NDEBUG)
int sqlite3PagerIswriteable(DbPage *pPg){
  return pPg->flags & PGHDR_WRITEABLE;
}
#endif

/*
** A call to this routine tells the pager that it is not necessary to
................................................................................
       || pPager->eState==PAGER_WRITER_DBMOD 
       || pPager->eState==PAGER_WRITER_LOCKED 
  );
  assert( assert_pager_state(pPager) );
  if( 0==pagerUseWal(pPager) ){
    rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
  }
#ifndef SQLITE_OMIT_CONCURRENT
  else{
    if( pPager->pAllRead ){
      /* This is an CONCURRENT transaction. Attempt to lock the wal database
      ** here. If SQLITE_BUSY (but not SQLITE_BUSY_SNAPSHOT) is returned,
      ** invoke the busy-handler and try again for as long as it returns
      ** non-zero.  */
      do {
        rc = sqlite3WalLockForCommit(pPager->pWal, pPage1, pPager->pAllRead);
      }while( rc==SQLITE_BUSY 
           && pPager->xBusyHandler(pPager->pBusyHandlerArg) 
      );
    }
  }
#endif /* SQLITE_OMIT_CONCURRENT */
  return rc;
}

#ifndef SQLITE_OMIT_CONCURRENT
/*
** This function is called as part of committing an CONCURRENT transaction.
** At this point the wal WRITER lock is held, and all pages in the cache 
** except for page 1 are compatible with the snapshot at the head of the
** wal file. 
**
** This function updates the in-memory data structures and reloads the
................................................................................
  if( rc==SQLITE_OK ){
    rc = readDbPage(pPage1, iFrame);
  }

  return rc;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** Set the in-memory cache of the database file size to nSz pages.
*/
void sqlite3PagerSetDbsize(Pager *pPager, Pgno nSz){
  pPager->dbSize = nSz;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** If this is a WAL mode connection and the WRITER lock is currently held,
** relinquish it.
*/
void sqlite3PagerDropExclusiveLock(Pager *pPager){
  if( pagerUseWal(pPager) ){
    sqlite3WalEndWriteTransaction(pPager->pWal);
  }
}
#endif  /* SQLITE_OMIT_CONCURRENT */


/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
** journal file. zMaster may be NULL, which is interpreted as no master
** journal (a single database transaction).

int sqlite3SectorSize(sqlite3_file *);

/* Functions used to truncate the database file. */
void sqlite3PagerTruncateImage(Pager*,Pgno);

void sqlite3PagerRekey(DbPage*, Pgno, u16);

#ifdef SQLITE_ENABLE_CONCURRENT
void sqlite3PagerEndConcurrent(Pager*);
int sqlite3PagerBeginConcurrent(Pager*);
void sqlite3PagerDropExclusiveLock(Pager*);
int sqlite3PagerUpgradeSnapshot(Pager *pPager, DbPage*);
void sqlite3PagerSetDbsize(Pager *pPager, Pgno);
int sqlite3PagerIsWal(Pager*);
#else

int sqlite3SectorSize(sqlite3_file *);

/* Functions used to truncate the database file. */
void sqlite3PagerTruncateImage(Pager*,Pgno);

void sqlite3PagerRekey(DbPage*, Pgno, u16);

#ifndef SQLITE_OMIT_CONCURRENT
void sqlite3PagerEndConcurrent(Pager*);
int sqlite3PagerBeginConcurrent(Pager*);
void sqlite3PagerDropExclusiveLock(Pager*);
int sqlite3PagerUpgradeSnapshot(Pager *pPager, DbPage*);
void sqlite3PagerSetDbsize(Pager *pPager, Pgno);
int sqlite3PagerIsWal(Pager*);
#else

#ifdef SQLITE_OMIT_TRUNCATE_OPTIMIZATION
  Tcl_SetVar2(interp, "sqlite_options", "truncate_opt", "0", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "truncate_opt", "1", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_ENABLE_CONCURRENT
  Tcl_SetVar2(interp, "sqlite_options", "concurrent", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "concurrent", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_OMIT_UTF16
  Tcl_SetVar2(interp, "sqlite_options", "utf16", "0", TCL_GLOBAL_ONLY);

#ifdef SQLITE_OMIT_TRUNCATE_OPTIMIZATION
  Tcl_SetVar2(interp, "sqlite_options", "truncate_opt", "0", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "truncate_opt", "1", TCL_GLOBAL_ONLY);
#endif

#ifndef SQLITE_OMIT_CONCURRENT
  Tcl_SetVar2(interp, "sqlite_options", "concurrent", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "concurrent", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_OMIT_UTF16
  Tcl_SetVar2(interp, "sqlite_options", "utf16", "0", TCL_GLOBAL_ONLY);

  assert( DbMaskTest(p->btreeMask, pOp->p1) );
  assert( p->readOnly==0 );
  pDb = &db->aDb[pOp->p1];
  assert( pDb->pBt!=0 );
  assert( sqlite3SchemaMutexHeld(db, pOp->p1, 0) );
  pIn3 = &aMem[pOp->p3];
  sqlite3VdbeMemIntegerify(pIn3);
#ifdef SQLITE_ENABLE_CONCURRENT
  if( db->bConcurrent 
   && (pOp->p2==BTREE_USER_VERSION || pOp->p2==BTREE_APPLICATION_ID)
  ){
    rc = SQLITE_ERROR;
    sqlite3VdbeError(p, "cannot modify %s within CONCURRENT transaction",
        pOp->p2==BTREE_USER_VERSION ? "user_version" : "application_id"
    );
................................................................................
** P2 contains the root-page of the table to lock.
**
** P4 contains a pointer to the name of the table being locked. This is only
** used to generate an error message if the lock cannot be obtained.
*/
case OP_TableLock: {
  u8 isWriteLock = (u8)pOp->p3;
#ifdef SQLITE_ENABLE_CONCURRENT
  if( isWriteLock && db->bConcurrent && pOp->p2==1 ){
    rc = SQLITE_ERROR;
    sqlite3VdbeError(p, 
        "cannot modify database schema within CONCURRENT transaction");
    break;
  }
#endif

  assert( DbMaskTest(p->btreeMask, pOp->p1) );
  assert( p->readOnly==0 );
  pDb = &db->aDb[pOp->p1];
  assert( pDb->pBt!=0 );
  assert( sqlite3SchemaMutexHeld(db, pOp->p1, 0) );
  pIn3 = &aMem[pOp->p3];
  sqlite3VdbeMemIntegerify(pIn3);
#ifndef SQLITE_OMIT_CONCURRENT
  if( db->bConcurrent 
   && (pOp->p2==BTREE_USER_VERSION || pOp->p2==BTREE_APPLICATION_ID)
  ){
    rc = SQLITE_ERROR;
    sqlite3VdbeError(p, "cannot modify %s within CONCURRENT transaction",
        pOp->p2==BTREE_USER_VERSION ? "user_version" : "application_id"
    );
................................................................................
** P2 contains the root-page of the table to lock.
**
** P4 contains a pointer to the name of the table being locked. This is only
** used to generate an error message if the lock cannot be obtained.
*/
case OP_TableLock: {
  u8 isWriteLock = (u8)pOp->p3;
#ifndef SQLITE_OMIT_CONCURRENT
  if( isWriteLock && db->bConcurrent && pOp->p2==1 ){
    rc = SQLITE_ERROR;
    sqlite3VdbeError(p, 
        "cannot modify database schema within CONCURRENT transaction");
    break;
  }
#endif

    if( sqlite3BtreeIsInTrans(pBt) ){
      needXcommit = 1;
      if( i!=1 ) nTrans++;
      rc = sqlite3BtreeExclusiveLock(pBt);
    }
  }

#ifdef SQLITE_ENABLE_CONCURRENT
  if( db->bConcurrent && (rc & 0xFF)==SQLITE_BUSY ){
    /* An SQLITE_BUSY or SQLITE_BUSY_SNAPSHOT was encountered while 
    ** attempting to take the WRITER lock on a wal file. Release the
    ** WRITER locks on all wal files and return early.  */
    for(i=0; i<db->nDb; i++){
      Btree *pBt = db->aDb[i].pBt;
      if( sqlite3BtreeIsInTrans(pBt) ){

    if( sqlite3BtreeIsInTrans(pBt) ){
      needXcommit = 1;
      if( i!=1 ) nTrans++;
      rc = sqlite3BtreeExclusiveLock(pBt);
    }
  }

#ifndef SQLITE_OMIT_CONCURRENT
  if( db->bConcurrent && (rc & 0xFF)==SQLITE_BUSY ){
    /* An SQLITE_BUSY or SQLITE_BUSY_SNAPSHOT was encountered while 
    ** attempting to take the WRITER lock on a wal file. Release the
    ** WRITER locks on all wal files and return early.  */
    for(i=0; i<db->nDb; i++){
      Btree *pBt = db->aDb[i].pBt;
      if( sqlite3BtreeIsInTrans(pBt) ){

  testcase( (rc&0xff)==SQLITE_IOERR );
  testcase( rc==SQLITE_PROTOCOL );
  testcase( rc==SQLITE_OK );
  return rc;
}


#ifdef SQLITE_ENABLE_CONCURRENT
/* 
** This function is only ever called when committing a "BEGIN CONCURRENT"
** transaction. It may be assumed that no frames have been written to
** the wal file. The second parameter is a pointer to the in-memory 
** representation of page 1 of the database (which may or may not be
** dirty). The third is a bitvec with a bit set for each page in the
** database file that was read by the current concurrent transaction.
................................................................................
      }
    }
  }

  return rc;
}


/*
** This function is called as part of committing an CONCURRENT transaction.
** It is assumed that sqlite3WalLockForCommit() has already been successfully
** called and so (a) the WRITER lock is held and (b) it is known that the
** wal-index-header stored in shared memory is not corrupt.
**
** Before returning, this function upgrades the client so that it is 
** operating on the database snapshot currently at the head of the wal file
................................................................................
  ** any reads performed between now and committing the transaction will
  ** read from the old snapshot - not the one just upgraded to.  */
  if( pWal->readLock==0 && pWal->hdr.mxFrame!=walCkptInfo(pWal)->nBackfill ){
    rc = walUpgradeReadlock(pWal);
  }
  return rc;
}
#endif   /* SQLITE_ENABLE_CONCURRENT */

/*
** End a write transaction.  The commit has already been done.  This
** routine merely releases the lock.
*/
int sqlite3WalEndWriteTransaction(Wal *pWal){
  if( pWal->writeLock ){

  testcase( (rc&0xff)==SQLITE_IOERR );
  testcase( rc==SQLITE_PROTOCOL );
  testcase( rc==SQLITE_OK );
  return rc;
}


#ifndef SQLITE_OMIT_CONCURRENT
/* 
** This function is only ever called when committing a "BEGIN CONCURRENT"
** transaction. It may be assumed that no frames have been written to
** the wal file. The second parameter is a pointer to the in-memory 
** representation of page 1 of the database (which may or may not be
** dirty). The third is a bitvec with a bit set for each page in the
** database file that was read by the current concurrent transaction.
................................................................................
      }
    }
  }

  return rc;
}

/* !defined(SQLITE_OMIT_CONCURRENT)
**
** This function is called as part of committing an CONCURRENT transaction.
** It is assumed that sqlite3WalLockForCommit() has already been successfully
** called and so (a) the WRITER lock is held and (b) it is known that the
** wal-index-header stored in shared memory is not corrupt.
**
** Before returning, this function upgrades the client so that it is 
** operating on the database snapshot currently at the head of the wal file
................................................................................
  ** any reads performed between now and committing the transaction will
  ** read from the old snapshot - not the one just upgraded to.  */
  if( pWal->readLock==0 && pWal->hdr.mxFrame!=walCkptInfo(pWal)->nBackfill ){
    rc = walUpgradeReadlock(pWal);
  }
  return rc;
}
#endif   /* SQLITE_OMIT_CONCURRENT */

/*
** End a write transaction.  The commit has already been done.  This
** routine merely releases the lock.
*/
int sqlite3WalEndWriteTransaction(Wal *pWal){
  if( pWal->writeLock ){

/* 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_CONCURRENT
/* Tell the wal layer that we want to commit a concurrent transaction */
int sqlite3WalLockForCommit(Wal *pWal, PgHdr *pPg, Bitvec *pRead);

/* Upgrade the state of the client to take into account changes written
** by other connections */
int sqlite3WalUpgradeSnapshot(Wal *pWal);
#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

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */

/* 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);

#ifndef SQLITE_OMIT_CONCURRENT
/* Tell the wal layer that we want to commit a concurrent transaction */
int sqlite3WalLockForCommit(Wal *pWal, PgHdr *pPg, Bitvec *pRead);

/* Upgrade the state of the client to take into account changes written
** by other connections */
int sqlite3WalUpgradeSnapshot(Wal *pWal);
#endif /* SQLITE_OMIT_CONCURRENT */

#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

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */