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8093 lines (7521 loc) · 268 KB
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/*
** 2004 April 6
**
** 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 a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"
/*
** The header string that appears at the beginning of every
** SQLite database.
*/
static const char zMagicHeader[] = SQLITE_FILE_HEADER;
/*
** Set this global variable to 1 to enable tracing using the TRACE
** macro.
*/
#if 0
int sqlite3BtreeTrace=1; /* True to enable tracing */
# define TRACE(X) if(sqlite3BtreeTrace){printf X;fflush(stdout);}
#else
# define TRACE(X)
#endif
/*
** Extract a 2-byte big-endian integer from an array of unsigned bytes.
** But if the value is zero, make it 65536.
**
** This routine is used to extract the "offset to cell content area" value
** from the header of a btree page. If the page size is 65536 and the page
** is empty, the offset should be 65536, but the 2-byte value stores zero.
** This routine makes the necessary adjustment to 65536.
*/
#define get2byteNotZero(X) (((((int)get2byte(X))-1)&0xffff)+1)
#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** A list of BtShared objects that are eligible for participation
** in shared cache. This variable has file scope during normal builds,
** but the test harness needs to access it so we make it global for
** test builds.
**
** Access to this variable is protected by SQLITE_MUTEX_STATIC_MASTER.
*/
#ifdef SQLITE_TEST
BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#else
static BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#endif
#endif /* SQLITE_OMIT_SHARED_CACHE */
#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Enable or disable the shared pager and schema features.
**
** This routine has no effect on existing database connections.
** The shared cache setting effects only future calls to
** sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().
*/
int sqlite3_enable_shared_cache(int enable){
sqlite3GlobalConfig.sharedCacheEnabled = enable;
return SQLITE_OK;
}
#endif
#ifdef SQLITE_OMIT_SHARED_CACHE
/*
** The functions querySharedCacheTableLock(), setSharedCacheTableLock(),
** and clearAllSharedCacheTableLocks()
** manipulate entries in the BtShared.pLock linked list used to store
** shared-cache table level locks. If the library is compiled with the
** shared-cache feature disabled, then there is only ever one user
** of each BtShared structure and so this locking is not necessary.
** So define the lock related functions as no-ops.
*/
#define querySharedCacheTableLock(a,b,c) SQLITE_OK
#define setSharedCacheTableLock(a,b,c) SQLITE_OK
#define clearAllSharedCacheTableLocks(a)
#define downgradeAllSharedCacheTableLocks(a)
#define hasSharedCacheTableLock(a,b,c,d) 1
#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;
for(p=sqliteHashFirst(&pSchema->idxHash); p; p=sqliteHashNext(p)){
Index *pIdx = (Index *)sqliteHashData(p);
if( pIdx->tnum==(int)iRoot ){
iTab = pIdx->pTable->tnum;
}
}
}else{
iTab = iRoot;
}
/* Search for the required lock. Either a write-lock on root-page iTab, a
** write-lock on the schema table, or (if the client is reading) a
** read-lock on iTab will suffice. Return 1 if any of these are found. */
for(pLock=pBtree->pBt->pLock; pLock; pLock=pLock->pNext){
if( pLock->pBtree==pBtree
&& (pLock->iTable==iTab || (pLock->eLock==WRITE_LOCK && pLock->iTable==1))
&& pLock->eLock>=eLockType
){
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
&& p->pBtree!=pBtree
&& 0==(p->pBtree->db->flags & SQLITE_ReadUncommitted)
){
return 1;
}
}
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;
assert( sqlite3BtreeHoldsMutex(p) );
assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
assert( p->db!=0 );
assert( !(p->db->flags&SQLITE_ReadUncommitted)||eLock==WRITE_LOCK||iTab==1 );
/* 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.
*/
if( pBt->pWriter!=p && pBt->isExclusive ){
sqlite3ConnectionBlocked(p->db, pBt->pWriter->db);
return SQLITE_LOCKED_SHAREDCACHE;
}
for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
/* The condition (pIter->eLock!=eLock) in the following if(...)
** statement is a simplification of:
**
** (eLock==WRITE_LOCK || pIter->eLock==WRITE_LOCK)
**
** since we know that if eLock==WRITE_LOCK, then no other connection
** may hold a WRITE_LOCK on any table in this file (since there can
** only be a single writer).
*/
assert( pIter->eLock==READ_LOCK || pIter->eLock==WRITE_LOCK );
assert( eLock==READ_LOCK || pIter->pBtree==p || pIter->eLock==READ_LOCK);
if( pIter->pBtree!=p && pIter->iTable==iTab && pIter->eLock!=eLock ){
sqlite3ConnectionBlocked(p->db, pIter->pBtree->db);
if( eLock==WRITE_LOCK ){
assert( p==pBt->pWriter );
pBt->isPending = 1;
}
return SQLITE_LOCKED_SHAREDCACHE;
}
}
return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */
#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** 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){
BtShared *pBt = p->pBt;
BtLock *pLock = 0;
BtLock *pIter;
assert( sqlite3BtreeHoldsMutex(p) );
assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
assert( p->db!=0 );
/* A connection with the read-uncommitted flag set will never try to
** obtain a read-lock using this function. The only read-lock obtained
** by a connection in read-uncommitted mode is on the sqlite_master
** table, and that lock is obtained in BtreeBeginTrans(). */
assert( 0==(p->db->flags&SQLITE_ReadUncommitted) || eLock==WRITE_LOCK );
/* This function should only be called on a sharable b-tree after it
** has been determined that no other b-tree holds a conflicting lock. */
assert( p->sharable );
assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );
/* First search the list for an existing lock on this table. */
for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
if( pIter->iTable==iTable && pIter->pBtree==p ){
pLock = pIter;
break;
}
}
/* If the above search did not find a BtLock struct associating Btree p
** with table iTable, allocate one and link it into the list.
*/
if( !pLock ){
pLock = (BtLock *)sqlite3MallocZero(sizeof(BtLock));
if( !pLock ){
return SQLITE_NOMEM;
}
pLock->iTable = iTable;
pLock->pBtree = p;
pLock->pNext = pBt->pLock;
pBt->pLock = pLock;
}
/* Set the BtLock.eLock variable to the maximum of the current lock
** and the requested lock. This means if a write-lock was already held
** and a read-lock requested, we don't incorrectly downgrade the lock.
*/
assert( WRITE_LOCK>READ_LOCK );
if( eLock>pLock->eLock ){
pLock->eLock = 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( sqlite3BtreeHoldsMutex(p) );
assert( p->sharable || 0==*ppIter );
assert( p->inTrans>0 );
while( *ppIter ){
BtLock *pLock = *ppIter;
assert( pBt->isExclusive==0 || pBt->pWriter==pLock->pBtree );
assert( pLock->pBtree->inTrans>=pLock->eLock );
if( pLock->pBtree==p ){
*ppIter = pLock->pNext;
assert( pLock->iTable!=1 || pLock==&p->lock );
if( pLock->iTable!=1 ){
sqlite3_free(pLock);
}
}else{
ppIter = &pLock->pNext;
}
}
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;
pBt->isPending = 0;
for(pLock=pBt->pLock; pLock; pLock=pLock->pNext){
assert( pLock->eLock==READ_LOCK || pLock->pBtree==p );
pLock->eLock = READ_LOCK;
}
}
}
#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
/*
** Invalidate the overflow page-list cache for cursor pCur, if any.
*/
static void invalidateOverflowCache(BtCursor *pCur){
assert( cursorHoldsMutex(pCur) );
sqlite3_free(pCur->aOverflow);
pCur->aOverflow = 0;
}
/*
** Invalidate the overflow page-list cache for all cursors opened
** on the shared btree structure pBt.
*/
static void invalidateAllOverflowCache(BtShared *pBt){
BtCursor *p;
assert( sqlite3_mutex_held(pBt->mutex) );
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;
BtShared *pBt = pBtree->pBt;
assert( sqlite3BtreeHoldsMutex(pBtree) );
for(p=pBt->pCursor; p; p=p->pNext){
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
** bug caused by the interaction of two useful IO optimizations surrounding
** free-list leaf pages:
**
** 1) When all data is deleted from a page and the page becomes
** a free-list leaf page, the page is not written to the database
** (as free-list leaf pages contain no meaningful data). Sometimes
** such a page is not even journalled (as it will not be modified,
** why bother journalling it?).
**
** 2) When a free-list leaf page is reused, its content is not read
** from the database or written to the journal file (why should it
** be, if it is not at all meaningful?).
**
** By themselves, these optimizations work fine and provide a handy
** performance boost to bulk delete or insert operations. However, if
** a page is moved to the free-list and then reused within the same
** transaction, a problem comes up. If the page is not journalled when
** it is moved to the free-list and it is also not journalled when it
** 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 ){
assert( pgno<=pBt->nPage );
pBt->pHasContent = sqlite3BitvecCreate(pBt->nPage);
if( !pBt->pHasContent ){
rc = SQLITE_NOMEM;
}
}
if( rc==SQLITE_OK && pgno<=sqlite3BitvecSize(pBt->pHasContent) ){
rc = sqlite3BitvecSet(pBt->pHasContent, pgno);
}
return rc;
}
/*
** Query the BtShared.pHasContent vector.
**
** This function is called when a free-list leaf page is removed from the
** free-list for reuse. It returns false if it is safe to retrieve the
** page from the pager layer with the 'no-content' flag set. True otherwise.
*/
static int btreeGetHasContent(BtShared *pBt, Pgno pgno){
Bitvec *p = pBt->pHasContent;
return (p && (pgno>sqlite3BitvecSize(p) || sqlite3BitvecTest(p, pgno)));
}
/*
** Clear (destroy) the BtShared.pHasContent bitvec. This should be
** invoked at the conclusion of each write-transaction.
*/
static void btreeClearHasContent(BtShared *pBt){
sqlite3BitvecDestroy(pBt->pHasContent);
pBt->pHasContent = 0;
}
/*
** Save the current cursor position in the variables BtCursor.nKey
** and BtCursor.pKey. The cursor's state is set to CURSOR_REQUIRESEEK.
**
** The caller must ensure that the cursor is valid (has eState==CURSOR_VALID)
** prior to calling this routine.
*/
static int saveCursorPosition(BtCursor *pCur){
int rc;
assert( CURSOR_VALID==pCur->eState );
assert( 0==pCur->pKey );
assert( cursorHoldsMutex(pCur) );
rc = sqlite3BtreeKeySize(pCur, &pCur->nKey);
assert( rc==SQLITE_OK ); /* KeySize() cannot fail */
/* If this is an intKey table, then the above call to BtreeKeySize()
** stores the integer key in pCur->nKey. In this case this value is
** all that is required. Otherwise, if pCur is not open on an intKey
** table, then malloc space for and store the pCur->nKey bytes of key
** data.
*/
if( 0==pCur->apPage[0]->intKey ){
void *pKey = sqlite3Malloc( (int)pCur->nKey );
if( pKey ){
rc = sqlite3BtreeKey(pCur, 0, (int)pCur->nKey, pKey);
if( rc==SQLITE_OK ){
pCur->pKey = pKey;
}else{
sqlite3_free(pKey);
}
}else{
rc = SQLITE_NOMEM;
}
}
assert( !pCur->apPage[0]->intKey || !pCur->pKey );
if( rc==SQLITE_OK ){
int i;
for(i=0; i<=pCur->iPage; i++){
releasePage(pCur->apPage[i]);
pCur->apPage[i] = 0;
}
pCur->iPage = -1;
pCur->eState = CURSOR_REQUIRESEEK;
}
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( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) &&
p->eState==CURSOR_VALID ){
int rc = saveCursorPosition(p);
if( SQLITE_OK!=rc ){
return rc;
}
}
}
return SQLITE_OK;
}
/*
** Clear the current cursor position.
*/
void sqlite3BtreeClearCursor(BtCursor *pCur){
assert( cursorHoldsMutex(pCur) );
sqlite3_free(pCur->pKey);
pCur->pKey = 0;
pCur->eState = CURSOR_INVALID;
}
/*
** In this version of BtreeMoveto, pKey is a packed index record
** such as is generated by the OP_MakeRecord opcode. Unpack the
** record and then call BtreeMovetoUnpacked() to do the work.
*/
static int btreeMoveto(
BtCursor *pCur, /* Cursor open on the btree to be searched */
const void *pKey, /* Packed key if the btree is an index */
i64 nKey, /* Integer key for tables. Size of pKey for indices */
int bias, /* Bias search to the high end */
int *pRes /* Write search results here */
){
int rc; /* Status code */
UnpackedRecord *pIdxKey; /* Unpacked index key */
char aSpace[150]; /* Temp space for pIdxKey - to avoid a malloc */
if( pKey ){
assert( nKey==(i64)(int)nKey );
pIdxKey = sqlite3VdbeRecordUnpack(pCur->pKeyInfo, (int)nKey, pKey,
aSpace, sizeof(aSpace));
if( pIdxKey==0 ) return SQLITE_NOMEM;
}else{
pIdxKey = 0;
}
rc = sqlite3BtreeMovetoUnpacked(pCur, pIdxKey, nKey, bias, pRes);
if( pKey ){
sqlite3VdbeDeleteUnpackedRecord(pIdxKey);
}
return rc;
}
/*
** Restore the cursor to the position it was in (or as close to as possible)
** when saveCursorPosition() was called. Note that this call deletes the
** saved position info stored by saveCursorPosition(), so there can be
** at most one effective restoreCursorPosition() call after each
** saveCursorPosition().
*/
static int btreeRestoreCursorPosition(BtCursor *pCur){
int rc;
assert( cursorHoldsMutex(pCur) );
assert( pCur->eState>=CURSOR_REQUIRESEEK );
if( pCur->eState==CURSOR_FAULT ){
return pCur->skipNext;
}
pCur->eState = CURSOR_INVALID;
rc = btreeMoveto(pCur, pCur->pKey, pCur->nKey, 0, &pCur->skipNext);
if( rc==SQLITE_OK ){
sqlite3_free(pCur->pKey);
pCur->pKey = 0;
assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_INVALID );
}
return rc;
}
#define restoreCursorPosition(p) \
(p->eState>=CURSOR_REQUIRESEEK ? \
btreeRestoreCursorPosition(p) : \
SQLITE_OK)
/*
** Determine whether or not a cursor has moved from the position it
** was last placed at. Cursors can move when the row they are pointing
** at is deleted out from under them.
**
** This routine returns an error code if something goes wrong. The
** integer *pHasMoved is set to one if the cursor has moved and 0 if not.
*/
int sqlite3BtreeCursorHasMoved(BtCursor *pCur, int *pHasMoved){
int rc;
rc = restoreCursorPosition(pCur);
if( rc ){
*pHasMoved = 1;
return rc;
}
if( pCur->eState!=CURSOR_VALID || pCur->skipNext!=0 ){
*pHasMoved = 1;
}else{
*pHasMoved = 0;
}
return SQLITE_OK;
}
#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page
** number for the pointer-map page that contains the entry for the
** input page number.
**
** Return 0 (not a valid page) for pgno==1 since there is
** no pointer map associated with page 1. The integrity_check logic
** requires that ptrmapPageno(*,1)!=1.
*/
static Pgno ptrmapPageno(BtShared *pBt, Pgno pgno){
int nPagesPerMapPage;
Pgno iPtrMap, ret;
assert( sqlite3_mutex_held(pBt->mutex) );
if( pgno<2 ) return 0;
nPagesPerMapPage = (pBt->usableSize/5)+1;
iPtrMap = (pgno-2)/nPagesPerMapPage;
ret = (iPtrMap*nPagesPerMapPage) + 2;
if( ret==PENDING_BYTE_PAGE(pBt) ){
ret++;
}
return ret;
}
/*
** Write an entry into the pointer map.
**
** This routine updates the pointer map entry for page number 'key'
** so that it maps to type 'eType' and parent page number 'pgno'.
**
** If *pRC is initially non-zero (non-SQLITE_OK) then this routine is
** a no-op. If an error occurs, the appropriate error code is written
** into *pRC.
*/
static void ptrmapPut(BtShared *pBt, Pgno key, u8 eType, Pgno parent, int *pRC){
DbPage *pDbPage; /* The pointer map page */
u8 *pPtrmap; /* The pointer map data */
Pgno iPtrmap; /* The pointer map page number */
int offset; /* Offset in pointer map page */
int rc; /* Return code from subfunctions */
if( *pRC ) return;
assert( sqlite3_mutex_held(pBt->mutex) );
/* The master-journal page number must never be used as a pointer map page */
assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );
assert( pBt->autoVacuum );
if( key==0 ){
*pRC = SQLITE_CORRUPT_BKPT;
return;
}
iPtrmap = PTRMAP_PAGENO(pBt, key);
rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
if( rc!=SQLITE_OK ){
*pRC = rc;
return;
}
offset = PTRMAP_PTROFFSET(iPtrmap, key);
if( offset<0 ){
*pRC = SQLITE_CORRUPT_BKPT;
goto ptrmap_exit;
}
pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);
if( eType!=pPtrmap[offset] || get4byte(&pPtrmap[offset+1])!=parent ){
TRACE(("PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent));
*pRC= rc = sqlite3PagerWrite(pDbPage);
if( rc==SQLITE_OK ){
pPtrmap[offset] = eType;
put4byte(&pPtrmap[offset+1], parent);
}
}
ptrmap_exit:
sqlite3PagerUnref(pDbPage);
}
/*
** Read an entry from the pointer map.
**
** This routine retrieves the pointer map entry for page 'key', writing
** the type and parent page number to *pEType and *pPgno respectively.
** An error code is returned if something goes wrong, otherwise SQLITE_OK.
*/
static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
DbPage *pDbPage; /* The pointer map page */
int iPtrmap; /* Pointer map page index */
u8 *pPtrmap; /* Pointer map page data */
int offset; /* Offset of entry in pointer map */
int rc;
assert( sqlite3_mutex_held(pBt->mutex) );
iPtrmap = PTRMAP_PAGENO(pBt, key);
rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
if( rc!=0 ){
return rc;
}
pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);
offset = PTRMAP_PTROFFSET(iPtrmap, key);
assert( pEType!=0 );
*pEType = pPtrmap[offset];
if( pPgno ) *pPgno = get4byte(&pPtrmap[offset+1]);
sqlite3PagerUnref(pDbPage);
if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT_BKPT;
return SQLITE_OK;
}
#else /* if defined SQLITE_OMIT_AUTOVACUUM */
#define ptrmapPut(w,x,y,z,rc)
#define ptrmapGet(w,x,y,z) SQLITE_OK
#define ptrmapPutOvflPtr(x, y, rc)
#endif
/*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
** This routine works only for pages that do not contain overflow cells.
*/
#define findCell(P,I) \
((P)->aData + ((P)->maskPage & get2byte(&(P)->aData[(P)->cellOffset+2*(I)])))
/*
** This a more complex version of findCell() that works for
** pages that do contain overflow cells.
*/
static u8 *findOverflowCell(MemPage *pPage, int iCell){
int i;
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
for(i=pPage->nOverflow-1; i>=0; i--){
int k;
struct _OvflCell *pOvfl;
pOvfl = &pPage->aOvfl[i];
k = pOvfl->idx;
if( k<=iCell ){
if( k==iCell ){
return pOvfl->pCell;
}
iCell--;
}
}
return findCell(pPage, iCell);
}
/*
** Parse a cell content block and fill in the CellInfo structure. There
** are two versions of this function. btreeParseCell() takes a
** cell index as the second argument and btreeParseCellPtr()
** takes a pointer to the body of the cell as its second argument.
**
** Within this file, the parseCell() macro can be called instead of
** btreeParseCellPtr(). Using some compilers, this will be faster.
*/
static void btreeParseCellPtr(
MemPage *pPage, /* Page containing the cell */
u8 *pCell, /* Pointer to the cell text. */
CellInfo *pInfo /* Fill in this structure */
){
u16 n; /* Number bytes in cell content header */
u32 nPayload; /* Number of bytes of cell payload */
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
pInfo->pCell = pCell;
assert( pPage->leaf==0 || pPage->leaf==1 );
n = pPage->childPtrSize;
assert( n==4-4*pPage->leaf );
if( pPage->intKey ){
if( pPage->hasData ){
n += getVarint32(&pCell[n], nPayload);
}else{
nPayload = 0;
}
n += getVarint(&pCell[n], (u64*)&pInfo->nKey);
pInfo->nData = nPayload;
}else{
pInfo->nData = 0;
n += getVarint32(&pCell[n], nPayload);
pInfo->nKey = nPayload;
}
pInfo->nPayload = nPayload;
pInfo->nHeader = n;
testcase( nPayload==pPage->maxLocal );
testcase( nPayload==pPage->maxLocal+1 );
if( likely(nPayload<=pPage->maxLocal) ){
/* This is the (easy) common case where the entire payload fits
** on the local page. No overflow is required.
*/
int nSize; /* Total size of cell content in bytes */
nSize = nPayload + n;
pInfo->nLocal = (u16)nPayload;
pInfo->iOverflow = 0;
if( (nSize & ~3)==0 ){
nSize = 4; /* Minimum cell size is 4 */
}
pInfo->nSize = (u16)nSize;
}else{
/* If the payload will not fit completely on the local page, we have
** to decide how much to store locally and how much to spill onto
** overflow pages. The strategy is to minimize the amount of unused
** space on overflow pages while keeping the amount of local storage
** in between minLocal and maxLocal.
**
** Warning: changing the way overflow payload is distributed in any
** way will result in an incompatible file format.
*/
int minLocal; /* Minimum amount of payload held locally */
int maxLocal; /* Maximum amount of payload held locally */
int surplus; /* Overflow payload available for local storage */
minLocal = pPage->minLocal;
maxLocal = pPage->maxLocal;
surplus = minLocal + (nPayload - minLocal)%(pPage->pBt->usableSize - 4);
testcase( surplus==maxLocal );
testcase( surplus==maxLocal+1 );
if( surplus <= maxLocal ){
pInfo->nLocal = (u16)surplus;
}else{
pInfo->nLocal = (u16)minLocal;
}
pInfo->iOverflow = (u16)(pInfo->nLocal + n);
pInfo->nSize = pInfo->iOverflow + 4;
}
}
#define parseCell(pPage, iCell, pInfo) \
btreeParseCellPtr((pPage), findCell((pPage), (iCell)), (pInfo))
static void btreeParseCell(
MemPage *pPage, /* Page containing the cell */
int iCell, /* The cell index. First cell is 0 */
CellInfo *pInfo /* Fill in this structure */
){
parseCell(pPage, iCell, pInfo);
}
/*
** Compute the total number of bytes that a Cell needs in the cell
** data area of the btree-page. The return number includes the cell
** data header and the local payload, but not any overflow page or
** the space used by the cell pointer.
*/
static u16 cellSizePtr(MemPage *pPage, u8 *pCell){
u8 *pIter = &pCell[pPage->childPtrSize];
u32 nSize;
#ifdef SQLITE_DEBUG
/* The value returned by this function should always be the same as
** the (CellInfo.nSize) value found by doing a full parse of the
** cell. If SQLITE_DEBUG is defined, an assert() at the bottom of
** this function verifies that this invariant is not violated. */
CellInfo debuginfo;
btreeParseCellPtr(pPage, pCell, &debuginfo);
#endif
if( pPage->intKey ){
u8 *pEnd;
if( pPage->hasData ){
pIter += getVarint32(pIter, nSize);
}else{
nSize = 0;
}
/* pIter now points at the 64-bit integer key value, a variable length
** integer. The following block moves pIter to point at the first byte
** past the end of the key value. */
pEnd = &pIter[9];
while( (*pIter++)&0x80 && pIter<pEnd );
}else{
pIter += getVarint32(pIter, nSize);