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Comment:Comment cleanup in btree.c.
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SHA1:32966ba4796e70d0afcff6abdda9bdcba08b098a
User & Date: drh 2009-10-16 15:05:19
Context
2009-10-16
16:21
Merge the sqlite3_reoptimize() changes into the trunk. check-in: 50136840 user: drh tags: trunk
15:05
Comment cleanup in btree.c. check-in: 32966ba4 user: drh tags: trunk
14:55
Experimental fix for [f777251dc7]. This may be changed yet. check-in: 174477bc user: dan tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/btree.c.

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  #define hasReadConflicts(a, b) 0
#endif

#ifndef SQLITE_OMIT_SHARED_CACHE

#ifdef SQLITE_DEBUG
/*
** This function is only used as part of an assert() statement. It checks

** that connection p holds the required locks to read or write to the 
** b-tree with root page iRoot. If so, true is returned. Otherwise, false. 


** For example, when writing to a table b-tree with root-page iRoot via 
** Btree connection pBtree:
**
**    assert( hasSharedCacheTableLock(pBtree, iRoot, 0, WRITE_LOCK) );
**
** When writing to an index b-tree that resides in a sharable database, the 
** caller should have first obtained a lock specifying the root page of
** the corresponding table b-tree. This makes things a bit more complicated,
** as this module treats each b-tree as a separate structure. To determine
** the table b-tree corresponding to the index b-tree being written, this
** function has to search through the database schema.
**
** Instead of a lock on the b-tree rooted at page iRoot, the caller may
** hold a write-lock on the schema table (root page 1). This is also
** acceptable.
*/
static int hasSharedCacheTableLock(
  Btree *pBtree,         /* Handle that must hold lock */
  Pgno iRoot,            /* Root page of b-tree */
  int isIndex,           /* True if iRoot is the root of an index b-tree */
  int eLockType          /* Required lock type (READ_LOCK or WRITE_LOCK) */
){
  Schema *pSchema = (Schema *)pBtree->pBt->pSchema;
  Pgno iTab = 0;
  BtLock *pLock;

  /* If this b-tree database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** In these cases return true immediately.  If the client is reading 
  ** or writing an index b-tree, but the schema is not loaded, then return
  ** true also. In this case the lock is required, but it is too difficult
  ** to check if the client actually holds it. This doesn't happen very
  ** often.  */
  if( (pBtree->sharable==0)
   || (eLockType==READ_LOCK && (pBtree->db->flags & SQLITE_ReadUncommitted))
   || (isIndex && (!pSchema || (pSchema->flags&DB_SchemaLoaded)==0 ))
  ){
    return 1;
  }










  /* Figure out the root-page that the lock should be held on. For table
  ** b-trees, this is just the root page of the b-tree being read or
  ** written. For index b-trees, it is the root page of the associated
  ** table.  */
  if( isIndex ){
    HashElem *p;
................................................................................
      return 1;
    }
  }

  /* Failed to find the required lock. */
  return 0;
}



/*
** This function is also used as part of assert() statements only. It 
** returns true if there exist one or more cursors open on the table 
** with root page iRoot that do not belong to either connection pBtree 








** or some other connection that has the read-uncommitted flag set.

**
** For example, before writing to page iRoot:

**
**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree *pBtree, Pgno iRoot){
  BtCursor *p;
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    if( p->pgnoRoot==iRoot 
................................................................................
    }
  }
  return 0;
}
#endif    /* #ifdef SQLITE_DEBUG */

/*
** Query to see if btree handle p may obtain a lock of type eLock 
** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
** SQLITE_OK if the lock may be obtained (by calling
** setSharedCacheTableLock()), or SQLITE_LOCKED if not.
*/
static int querySharedCacheTableLock(Btree *p, Pgno iTab, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pIter;
................................................................................
  /* If requesting a write-lock, then the Btree must have an open write
  ** transaction on this file. And, obviously, for this to be so there 
  ** must be an open write transaction on the file itself.
  */
  assert( eLock==READ_LOCK || (p==pBt->pWriter && p->inTrans==TRANS_WRITE) );
  assert( eLock==READ_LOCK || pBt->inTransaction==TRANS_WRITE );
  
  /* This is a no-op if the shared-cache is not enabled */
  if( !p->sharable ){
    return SQLITE_OK;
  }

  /* If some other connection is holding an exclusive lock, the
  ** requested lock may not be obtained.
  */
................................................................................
/*
** Add a lock on the table with root-page iTable to the shared-btree used
** by Btree handle p. Parameter eLock must be either READ_LOCK or 
** WRITE_LOCK.
**
** This function assumes the following:
**
**   (a) The specified b-tree connection handle is connected to a sharable
**       b-tree database (one with the BtShared.sharable) flag set, and
**
**   (b) No other b-tree connection handle holds a lock that conflicts
**       with the requested lock (i.e. querySharedCacheTableLock() has
**       already been called and returned SQLITE_OK).
**
** SQLITE_OK is returned if the lock is added successfully. SQLITE_NOMEM 
** is returned if a malloc attempt fails.
*/
static int setSharedCacheTableLock(Btree *p, Pgno iTable, u8 eLock){
................................................................................
  return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Release all the table locks (locks obtained via calls to
** the setSharedCacheTableLock() procedure) held by Btree handle p.
**
** This function assumes that handle p has an open read or write 
** transaction. If it does not, then the BtShared.isPending variable
** may be incorrectly cleared.
*/
static void clearAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  BtLock **ppIter = &pBt->pLock;

................................................................................

  assert( pBt->isPending==0 || pBt->pWriter );
  if( pBt->pWriter==p ){
    pBt->pWriter = 0;
    pBt->isExclusive = 0;
    pBt->isPending = 0;
  }else if( pBt->nTransaction==2 ){
    /* This function is called when connection p is concluding its 
    ** transaction. If there currently exists a writer, and p is not
    ** that writer, then the number of locks held by connections other
    ** than the writer must be about to drop to zero. In this case
    ** set the isPending flag to 0.
    **
    ** If there is not currently a writer, then BtShared.isPending must
    ** be zero already. So this next line is harmless in that case.
    */
    pBt->isPending = 0;
  }
}

/*
** This function changes all write-locks held by connection p to read-locks.
*/
static void downgradeAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  if( pBt->pWriter==p ){
    BtLock *pLock;
    pBt->pWriter = 0;
    pBt->isExclusive = 0;
................................................................................
}

#endif /* SQLITE_OMIT_SHARED_CACHE */

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

/*


** Verify that the cursor holds a mutex on the BtShared
*/
#ifndef NDEBUG

static int cursorHoldsMutex(BtCursor *p){
  return sqlite3_mutex_held(p->pBt->mutex);
}
#endif


#ifndef SQLITE_OMIT_INCRBLOB
................................................................................
  for(p=pBt->pCursor; p; p=p->pNext){
    invalidateOverflowCache(p);
  }
}

/*
** This function is called before modifying the contents of a table
** b-tree to invalidate any incrblob cursors that are open on the
** row or one of the rows being modified.
**
** If argument isClearTable is true, then the entire contents of the
** table is about to be deleted. In this case invalidate all incrblob
** cursors open on any row within the table with root-page pgnoRoot.
**
** Otherwise, if argument isClearTable is false, then the row with
** rowid iRow is being replaced or deleted. In this case invalidate
** only those incrblob cursors open on this specific row.
*/
static void invalidateIncrblobCursors(
  Btree *pBtree,          /* The database file to check */
  i64 iRow,               /* The rowid that might be changing */
  int isClearTable        /* True if all rows are being deleted */
){
  BtCursor *p;
................................................................................
    if( p->isIncrblobHandle && (isClearTable || p->info.nKey==iRow) ){
      p->eState = CURSOR_INVALID;
    }
  }
}

#else

  #define invalidateOverflowCache(x)
  #define invalidateAllOverflowCache(x)
  #define invalidateIncrblobCursors(x,y,z)
#endif

/*
** Set bit pgno of the BtShared.pHasContent bitvec. This is called 
** when a page that previously contained data becomes a free-list leaf 
** page.
**
** The BtShared.pHasContent bitvec exists to work around an obscure
................................................................................
** is extracted from the free-list and reused, then the original data
** may be lost. In the event of a rollback, it may not be possible
** to restore the database to its original configuration.
**
** The solution is the BtShared.pHasContent bitvec. Whenever a page is 
** moved to become a free-list leaf page, the corresponding bit is
** set in the bitvec. Whenever a leaf page is extracted from the free-list,
** optimization 2 above is ommitted if the corresponding bit is already
** set in BtShared.pHasContent. The contents of the bitvec are cleared
** at the end of every transaction.
*/
static int btreeSetHasContent(BtShared *pBt, Pgno pgno){
  int rc = SQLITE_OK;
  if( !pBt->pHasContent ){
    int nPage = 100;
................................................................................
  }

  invalidateOverflowCache(pCur);
  return rc;
}

/*
** Save the positions of all cursors except pExcept open on the table 
** with root-page iRoot. Usually, this is called just before cursor
** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
*/
static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
  BtCursor *p;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pExcept==0 || pExcept->pBt==pBt );
  for(p=pBt->pCursor; p; p=p->pNext){
................................................................................
  if( nSize<4 ){
    nSize = 4;
  }

  assert( nSize==debuginfo.nSize );
  return (u16)nSize;
}
#ifndef NDEBUG




static u16 cellSize(MemPage *pPage, int iCell){
  return cellSizePtr(pPage, findCell(pPage, iCell));
}
#endif

#ifndef SQLITE_OMIT_AUTOVACUUM
/*







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  #define hasReadConflicts(a, b) 0
#endif

#ifndef SQLITE_OMIT_SHARED_CACHE

#ifdef SQLITE_DEBUG
/*
**** This function is only used as part of an assert() statement. ***
**
** Check to see if pBtree holds the required locks to read or write to the 

** table with root page iRoot.   Return 1 if it does and 0 if not.
**
** For example, when writing to a table with root-page iRoot via 
** Btree connection pBtree:
**
**    assert( hasSharedCacheTableLock(pBtree, iRoot, 0, WRITE_LOCK) );
**
** When writing to an index that resides in a sharable database, the 
** caller should have first obtained a lock specifying the root page of
** the corresponding table. This makes things a bit more complicated,
** as this module treats each table as a separate structure. To determine
** the table corresponding to the index being written, this
** function has to search through the database schema.
**
** Instead of a lock on the table/index rooted at page iRoot, the caller may
** hold a write-lock on the schema table (root page 1). This is also
** acceptable.
*/
static int hasSharedCacheTableLock(
  Btree *pBtree,         /* Handle that must hold lock */
  Pgno iRoot,            /* Root page of b-tree */
  int isIndex,           /* True if iRoot is the root of an index b-tree */
  int eLockType          /* Required lock type (READ_LOCK or WRITE_LOCK) */
){
  Schema *pSchema = (Schema *)pBtree->pBt->pSchema;
  Pgno iTab = 0;
  BtLock *pLock;

  /* If this database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** Return true immediately.
  */



  if( (pBtree->sharable==0)
   || (eLockType==READ_LOCK && (pBtree->db->flags & SQLITE_ReadUncommitted))

  ){
    return 1;
  }

  /* If the client is reading  or writing an index and the schema is
  ** not loaded, then it is too difficult to actually check to see if
  ** the correct locks are held.  So do not bother - just return true.
  ** This case does not come up very often anyhow.
  */
  if( isIndex && (!pSchema || (pSchema->flags&DB_SchemaLoaded)==0) ){
    return 1;
  }

  /* Figure out the root-page that the lock should be held on. For table
  ** b-trees, this is just the root page of the b-tree being read or
  ** written. For index b-trees, it is the root page of the associated
  ** table.  */
  if( isIndex ){
    HashElem *p;
................................................................................
      return 1;
    }
  }

  /* Failed to find the required lock. */
  return 0;
}
#endif /* SQLITE_DEBUG */

#ifdef SQLITE_DEBUG
/*
**** This function may be used as part of assert() statements only. ****


**
** Return true if it would be illegal for pBtree to write into the
** table or index rooted at iRoot because other shared connections are
** simultaneously reading that same table or index.
**
** It is illegal for pBtree to write if some other Btree object that
** shares the same BtShared object is currently reading or writing
** the iRoot table.  Except, if the other Btree object has the
** read-uncommitted flag set, then it is OK for the other object to
** have a read cursor.
**
** For example, before writing to any part of the table or index
** rooted at page iRoot, one should call:
**
**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree *pBtree, Pgno iRoot){
  BtCursor *p;
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    if( p->pgnoRoot==iRoot 
................................................................................
    }
  }
  return 0;
}
#endif    /* #ifdef SQLITE_DEBUG */

/*
** Query to see if Btree handle p may obtain a lock of type eLock 
** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
** SQLITE_OK if the lock may be obtained (by calling
** setSharedCacheTableLock()), or SQLITE_LOCKED if not.
*/
static int querySharedCacheTableLock(Btree *p, Pgno iTab, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pIter;
................................................................................
  /* If requesting a write-lock, then the Btree must have an open write
  ** transaction on this file. And, obviously, for this to be so there 
  ** must be an open write transaction on the file itself.
  */
  assert( eLock==READ_LOCK || (p==pBt->pWriter && p->inTrans==TRANS_WRITE) );
  assert( eLock==READ_LOCK || pBt->inTransaction==TRANS_WRITE );
  
  /* This routine is a no-op if the shared-cache is not enabled */
  if( !p->sharable ){
    return SQLITE_OK;
  }

  /* If some other connection is holding an exclusive lock, the
  ** requested lock may not be obtained.
  */
................................................................................
/*
** Add a lock on the table with root-page iTable to the shared-btree used
** by Btree handle p. Parameter eLock must be either READ_LOCK or 
** WRITE_LOCK.
**
** This function assumes the following:
**
**   (a) The specified Btree object p is connected to a sharable
**       database (one with the BtShared.sharable flag set), and
**
**   (b) No other Btree objects hold a lock that conflicts
**       with the requested lock (i.e. querySharedCacheTableLock() has
**       already been called and returned SQLITE_OK).
**
** SQLITE_OK is returned if the lock is added successfully. SQLITE_NOMEM 
** is returned if a malloc attempt fails.
*/
static int setSharedCacheTableLock(Btree *p, Pgno iTable, u8 eLock){
................................................................................
  return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Release all the table locks (locks obtained via calls to
** the setSharedCacheTableLock() procedure) held by Btree object p.
**
** This function assumes that Btree p has an open read or write 
** transaction. If it does not, then the BtShared.isPending variable
** may be incorrectly cleared.
*/
static void clearAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  BtLock **ppIter = &pBt->pLock;

................................................................................

  assert( pBt->isPending==0 || pBt->pWriter );
  if( pBt->pWriter==p ){
    pBt->pWriter = 0;
    pBt->isExclusive = 0;
    pBt->isPending = 0;
  }else if( pBt->nTransaction==2 ){
    /* This function is called when Btree p is concluding its 
    ** transaction. If there currently exists a writer, and p is not
    ** that writer, then the number of locks held by connections other
    ** than the writer must be about to drop to zero. In this case
    ** set the isPending flag to 0.
    **
    ** If there is not currently a writer, then BtShared.isPending must
    ** be zero already. So this next line is harmless in that case.
    */
    pBt->isPending = 0;
  }
}

/*
** This function changes all write-locks held by Btree p into read-locks.
*/
static void downgradeAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  if( pBt->pWriter==p ){
    BtLock *pLock;
    pBt->pWriter = 0;
    pBt->isExclusive = 0;
................................................................................
}

#endif /* SQLITE_OMIT_SHARED_CACHE */

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
*/

#ifdef SQLITE_DEBUG
static int cursorHoldsMutex(BtCursor *p){
  return sqlite3_mutex_held(p->pBt->mutex);
}
#endif


#ifndef SQLITE_OMIT_INCRBLOB
................................................................................
  for(p=pBt->pCursor; p; p=p->pNext){
    invalidateOverflowCache(p);
  }
}

/*
** This function is called before modifying the contents of a table
** to invalidate any incrblob cursors that are open on the
** row or one of the rows being modified.
**
** If argument isClearTable is true, then the entire contents of the
** table is about to be deleted. In this case invalidate all incrblob
** cursors open on any row within the table with root-page pgnoRoot.
**
** Otherwise, if argument isClearTable is false, then the row with
** rowid iRow is being replaced or deleted. In this case invalidate
** only those incrblob cursors open on that specific row.
*/
static void invalidateIncrblobCursors(
  Btree *pBtree,          /* The database file to check */
  i64 iRow,               /* The rowid that might be changing */
  int isClearTable        /* True if all rows are being deleted */
){
  BtCursor *p;
................................................................................
    if( p->isIncrblobHandle && (isClearTable || p->info.nKey==iRow) ){
      p->eState = CURSOR_INVALID;
    }
  }
}

#else
  /* Stub functions when INCRBLOB is omitted */
  #define invalidateOverflowCache(x)
  #define invalidateAllOverflowCache(x)
  #define invalidateIncrblobCursors(x,y,z)
#endif /* SQLITE_OMIT_INCRBLOB */

/*
** Set bit pgno of the BtShared.pHasContent bitvec. This is called 
** when a page that previously contained data becomes a free-list leaf 
** page.
**
** The BtShared.pHasContent bitvec exists to work around an obscure
................................................................................
** is extracted from the free-list and reused, then the original data
** may be lost. In the event of a rollback, it may not be possible
** to restore the database to its original configuration.
**
** The solution is the BtShared.pHasContent bitvec. Whenever a page is 
** moved to become a free-list leaf page, the corresponding bit is
** set in the bitvec. Whenever a leaf page is extracted from the free-list,
** optimization 2 above is omitted if the corresponding bit is already
** set in BtShared.pHasContent. The contents of the bitvec are cleared
** at the end of every transaction.
*/
static int btreeSetHasContent(BtShared *pBt, Pgno pgno){
  int rc = SQLITE_OK;
  if( !pBt->pHasContent ){
    int nPage = 100;
................................................................................
  }

  invalidateOverflowCache(pCur);
  return rc;
}

/*
** Save the positions of all cursors (except pExcept) that are open on
** the table  with root-page iRoot. Usually, this is called just before cursor
** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
*/
static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
  BtCursor *p;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pExcept==0 || pExcept->pBt==pBt );
  for(p=pBt->pCursor; p; p=p->pNext){
................................................................................
  if( nSize<4 ){
    nSize = 4;
  }

  assert( nSize==debuginfo.nSize );
  return (u16)nSize;
}


#ifdef SQLITE_DEBUG
/* This variation on cellSizePtr() is used inside of assert() statements
** only. */
static u16 cellSize(MemPage *pPage, int iCell){
  return cellSizePtr(pPage, findCell(pPage, iCell));
}
#endif

#ifndef SQLITE_OMIT_AUTOVACUUM
/*