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sqlcipher/src/rowset.c

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/*
** 2008 December 3
**
** 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 module implements an object we call a "RowSet".
**
** The RowSet object is a collection of rowids. Rowids
** are inserted into the RowSet in an arbitrary order. Inserts
** can be intermixed with tests to see if a given rowid has been
** previously inserted into the RowSet.
**
** After all inserts are finished, it is possible to extract the
** elements of the RowSet in sorted order. Once this extraction
** process has started, no new elements may be inserted.
**
** Hence, the primitive operations for a RowSet are:
**
** CREATE
** INSERT
** TEST
** SMALLEST
** DESTROY
**
** The CREATE and DESTROY primitives are the constructor and destructor,
** obviously. The INSERT primitive adds a new element to the RowSet.
** TEST checks to see if an element is already in the RowSet. SMALLEST
** extracts the least value from the RowSet.
**
** The INSERT primitive might allocate additional memory. Memory is
** allocated in chunks so most INSERTs do no allocation. There is an
** upper bound on the size of allocated memory. No memory is freed
** until DESTROY.
**
** The TEST primitive includes a "batch" number. The TEST primitive
** will only see elements that were inserted before the last change
** in the batch number. In other words, if an INSERT occurs between
** two TESTs where the TESTs have the same batch nubmer, then the
** value added by the INSERT will not be visible to the second TEST.
** The initial batch number is zero, so if the very first TEST contains
** a non-zero batch number, it will see all prior INSERTs.
**
** No INSERTs may occurs after a SMALLEST. An assertion will fail if
** that is attempted.
**
** The cost of an INSERT is roughly constant. (Sometimes new memory
** has to be allocated on an INSERT.) The cost of a TEST with a new
** batch number is O(NlogN) where N is the number of elements in the RowSet.
** The cost of a TEST using the same batch number is O(logN). The cost
** of the first SMALLEST is O(NlogN). Second and subsequent SMALLEST
** primitives are constant time. The cost of DESTROY is O(N).
**
** TEST and SMALLEST may not be used by the same RowSet. This used to
** be possible, but the feature was not used, so it was removed in order
** to simplify the code.
*/
#include "sqliteInt.h"
/*
** Target size for allocation chunks.
*/
#define ROWSET_ALLOCATION_SIZE 1024
/*
** The number of rowset entries per allocation chunk.
*/
#define ROWSET_ENTRY_PER_CHUNK \
((ROWSET_ALLOCATION_SIZE-8)/sizeof(struct RowSetEntry))
/*
** Each entry in a RowSet is an instance of the following object.
**
** This same object is reused to store a linked list of trees of RowSetEntry
** objects. In that alternative use, pRight points to the next entry
** in the list, pLeft points to the tree, and v is unused. The
** RowSet.pForest value points to the head of this forest list.
*/
struct RowSetEntry {
i64 v; /* ROWID value for this entry */
struct RowSetEntry *pRight; /* Right subtree (larger entries) or list */
struct RowSetEntry *pLeft; /* Left subtree (smaller entries) */
};
/*
** RowSetEntry objects are allocated in large chunks (instances of the
** following structure) to reduce memory allocation overhead. The
** chunks are kept on a linked list so that they can be deallocated
** when the RowSet is destroyed.
*/
struct RowSetChunk {
struct RowSetChunk *pNextChunk; /* Next chunk on list of them all */
struct RowSetEntry aEntry[ROWSET_ENTRY_PER_CHUNK]; /* Allocated entries */
};
/*
** A RowSet in an instance of the following structure.
**
** A typedef of this structure if found in sqliteInt.h.
*/
struct RowSet {
struct RowSetChunk *pChunk; /* List of all chunk allocations */
sqlite3 *db; /* The database connection */
struct RowSetEntry *pEntry; /* List of entries using pRight */
struct RowSetEntry *pLast; /* Last entry on the pEntry list */
struct RowSetEntry *pFresh; /* Source of new entry objects */
struct RowSetEntry *pForest; /* List of binary trees of entries */
u16 nFresh; /* Number of objects on pFresh */
u16 rsFlags; /* Various flags */
int iBatch; /* Current insert batch */
};
/*
** Allowed values for RowSet.rsFlags
*/
#define ROWSET_SORTED 0x01 /* True if RowSet.pEntry is sorted */
#define ROWSET_NEXT 0x02 /* True if sqlite3RowSetNext() has been called */
/*
** Allocate a RowSet object. Return NULL if a memory allocation
** error occurs.
*/
RowSet *sqlite3RowSetInit(sqlite3 *db){
RowSet *p = sqlite3DbMallocRawNN(db, sizeof(*p));
if( p ){
int N = sqlite3DbMallocSize(db, p);
p->pChunk = 0;
p->db = db;
p->pEntry = 0;
p->pLast = 0;
p->pForest = 0;
p->pFresh = (struct RowSetEntry*)(ROUND8(sizeof(*p)) + (char*)p);
p->nFresh = (u16)((N - ROUND8(sizeof(*p)))/sizeof(struct RowSetEntry));
p->rsFlags = ROWSET_SORTED;
p->iBatch = 0;
}
return p;
}
/*
** Deallocate all chunks from a RowSet. This frees all memory that
** the RowSet has allocated over its lifetime. This routine is
** the destructor for the RowSet.
*/
void sqlite3RowSetClear(void *pArg){
RowSet *p = (RowSet*)pArg;
struct RowSetChunk *pChunk, *pNextChunk;
for(pChunk=p->pChunk; pChunk; pChunk = pNextChunk){
pNextChunk = pChunk->pNextChunk;
sqlite3DbFree(p->db, pChunk);
}
p->pChunk = 0;
p->nFresh = 0;
p->pEntry = 0;
p->pLast = 0;
p->pForest = 0;
p->rsFlags = ROWSET_SORTED;
}
/*
** Deallocate all chunks from a RowSet. This frees all memory that
** the RowSet has allocated over its lifetime. This routine is
** the destructor for the RowSet.
*/
void sqlite3RowSetDelete(void *pArg){
sqlite3RowSetClear(pArg);
sqlite3DbFree(((RowSet*)pArg)->db, pArg);
}
/*
** Allocate a new RowSetEntry object that is associated with the
** given RowSet. Return a pointer to the new and completely uninitialized
** objected.
**
** In an OOM situation, the RowSet.db->mallocFailed flag is set and this
** routine returns NULL.
*/
static struct RowSetEntry *rowSetEntryAlloc(RowSet *p){
assert( p!=0 );
if( p->nFresh==0 ){ /*OPTIMIZATION-IF-FALSE*/
/* We could allocate a fresh RowSetEntry each time one is needed, but it
** is more efficient to pull a preallocated entry from the pool */
struct RowSetChunk *pNew;
pNew = sqlite3DbMallocRawNN(p->db, sizeof(*pNew));
if( pNew==0 ){
return 0;
}
pNew->pNextChunk = p->pChunk;
p->pChunk = pNew;
p->pFresh = pNew->aEntry;
p->nFresh = ROWSET_ENTRY_PER_CHUNK;
}
p->nFresh--;
return p->pFresh++;
}
/*
** Insert a new value into a RowSet.
**
** The mallocFailed flag of the database connection is set if a
** memory allocation fails.
*/
void sqlite3RowSetInsert(RowSet *p, i64 rowid){
struct RowSetEntry *pEntry; /* The new entry */
struct RowSetEntry *pLast; /* The last prior entry */
/* This routine is never called after sqlite3RowSetNext() */
assert( p!=0 && (p->rsFlags & ROWSET_NEXT)==0 );
pEntry = rowSetEntryAlloc(p);
if( pEntry==0 ) return;
pEntry->v = rowid;
pEntry->pRight = 0;
pLast = p->pLast;
if( pLast ){
if( rowid<=pLast->v ){ /*OPTIMIZATION-IF-FALSE*/
/* Avoid unnecessary sorts by preserving the ROWSET_SORTED flags
** where possible */
p->rsFlags &= ~ROWSET_SORTED;
}
pLast->pRight = pEntry;
}else{
p->pEntry = pEntry;
}
p->pLast = pEntry;
}
/*
** Merge two lists of RowSetEntry objects. Remove duplicates.
**
** The input lists are connected via pRight pointers and are
** assumed to each already be in sorted order.
*/
static struct RowSetEntry *rowSetEntryMerge(
struct RowSetEntry *pA, /* First sorted list to be merged */
struct RowSetEntry *pB /* Second sorted list to be merged */
){
struct RowSetEntry head;
struct RowSetEntry *pTail;
pTail = &head;
assert( pA!=0 && pB!=0 );
for(;;){
assert( pA->pRight==0 || pA->v<=pA->pRight->v );
assert( pB->pRight==0 || pB->v<=pB->pRight->v );
if( pA->v<=pB->v ){
if( pA->v<pB->v ) pTail = pTail->pRight = pA;
pA = pA->pRight;
if( pA==0 ){
pTail->pRight = pB;
break;
}
}else{
pTail = pTail->pRight = pB;
pB = pB->pRight;
if( pB==0 ){
pTail->pRight = pA;
break;
}
}
}
return head.pRight;
}
/*
** Sort all elements on the list of RowSetEntry objects into order of
** increasing v.
*/
static struct RowSetEntry *rowSetEntrySort(struct RowSetEntry *pIn){
unsigned int i;
struct RowSetEntry *pNext, *aBucket[40];
memset(aBucket, 0, sizeof(aBucket));
while( pIn ){
pNext = pIn->pRight;
pIn->pRight = 0;
for(i=0; aBucket[i]; i++){
pIn = rowSetEntryMerge(aBucket[i], pIn);
aBucket[i] = 0;
}
aBucket[i] = pIn;
pIn = pNext;
}
pIn = aBucket[0];
for(i=1; i<sizeof(aBucket)/sizeof(aBucket[0]); i++){
if( aBucket[i]==0 ) continue;
pIn = pIn ? rowSetEntryMerge(pIn, aBucket[i]) : aBucket[i];
}
return pIn;
}
/*
** The input, pIn, is a binary tree (or subtree) of RowSetEntry objects.
** Convert this tree into a linked list connected by the pRight pointers
** and return pointers to the first and last elements of the new list.
*/
static void rowSetTreeToList(
struct RowSetEntry *pIn, /* Root of the input tree */
struct RowSetEntry **ppFirst, /* Write head of the output list here */
struct RowSetEntry **ppLast /* Write tail of the output list here */
){
assert( pIn!=0 );
if( pIn->pLeft ){
struct RowSetEntry *p;
rowSetTreeToList(pIn->pLeft, ppFirst, &p);
p->pRight = pIn;
}else{
*ppFirst = pIn;
}
if( pIn->pRight ){
rowSetTreeToList(pIn->pRight, &pIn->pRight, ppLast);
}else{
*ppLast = pIn;
}
assert( (*ppLast)->pRight==0 );
}
/*
** Convert a sorted list of elements (connected by pRight) into a binary
** tree with depth of iDepth. A depth of 1 means the tree contains a single
** node taken from the head of *ppList. A depth of 2 means a tree with
** three nodes. And so forth.
**
** Use as many entries from the input list as required and update the
** *ppList to point to the unused elements of the list. If the input
** list contains too few elements, then construct an incomplete tree
** and leave *ppList set to NULL.
**
** Return a pointer to the root of the constructed binary tree.
*/
static struct RowSetEntry *rowSetNDeepTree(
struct RowSetEntry **ppList,
int iDepth
){
struct RowSetEntry *p; /* Root of the new tree */
struct RowSetEntry *pLeft; /* Left subtree */
if( *ppList==0 ){ /*OPTIMIZATION-IF-TRUE*/
/* Prevent unnecessary deep recursion when we run out of entries */
return 0;
}
if( iDepth>1 ){ /*OPTIMIZATION-IF-TRUE*/
/* This branch causes a *balanced* tree to be generated. A valid tree
** is still generated without this branch, but the tree is wildly
** unbalanced and inefficient. */
pLeft = rowSetNDeepTree(ppList, iDepth-1);
p = *ppList;
if( p==0 ){ /*OPTIMIZATION-IF-FALSE*/
/* It is safe to always return here, but the resulting tree
** would be unbalanced */
return pLeft;
}
p->pLeft = pLeft;
*ppList = p->pRight;
p->pRight = rowSetNDeepTree(ppList, iDepth-1);
}else{
p = *ppList;
*ppList = p->pRight;
p->pLeft = p->pRight = 0;
}
return p;
}
/*
** Convert a sorted list of elements into a binary tree. Make the tree
** as deep as it needs to be in order to contain the entire list.
*/
static struct RowSetEntry *rowSetListToTree(struct RowSetEntry *pList){
int iDepth; /* Depth of the tree so far */
struct RowSetEntry *p; /* Current tree root */
struct RowSetEntry *pLeft; /* Left subtree */
assert( pList!=0 );
p = pList;
pList = p->pRight;
p->pLeft = p->pRight = 0;
for(iDepth=1; pList; iDepth++){
pLeft = p;
p = pList;
pList = p->pRight;
p->pLeft = pLeft;
p->pRight = rowSetNDeepTree(&pList, iDepth);
}
return p;
}
/*
** Extract the smallest element from the RowSet.
** Write the element into *pRowid. Return 1 on success. Return
** 0 if the RowSet is already empty.
**
** After this routine has been called, the sqlite3RowSetInsert()
** routine may not be called again.
**
** This routine may not be called after sqlite3RowSetTest() has
** been used. Older versions of RowSet allowed that, but as the
** capability was not used by the code generator, it was removed
** for code economy.
*/
int sqlite3RowSetNext(RowSet *p, i64 *pRowid){
assert( p!=0 );
assert( p->pForest==0 ); /* Cannot be used with sqlite3RowSetText() */
/* Merge the forest into a single sorted list on first call */
if( (p->rsFlags & ROWSET_NEXT)==0 ){ /*OPTIMIZATION-IF-FALSE*/
if( (p->rsFlags & ROWSET_SORTED)==0 ){ /*OPTIMIZATION-IF-FALSE*/
p->pEntry = rowSetEntrySort(p->pEntry);
}
p->rsFlags |= ROWSET_SORTED|ROWSET_NEXT;
}
/* Return the next entry on the list */
if( p->pEntry ){
*pRowid = p->pEntry->v;
p->pEntry = p->pEntry->pRight;
if( p->pEntry==0 ){ /*OPTIMIZATION-IF-TRUE*/
/* Free memory immediately, rather than waiting on sqlite3_finalize() */
sqlite3RowSetClear(p);
}
return 1;
}else{
return 0;
}
}
/*
** Check to see if element iRowid was inserted into the rowset as
** part of any insert batch prior to iBatch. Return 1 or 0.
**
** If this is the first test of a new batch and if there exist entries
** on pRowSet->pEntry, then sort those entries into the forest at
** pRowSet->pForest so that they can be tested.
*/
int sqlite3RowSetTest(RowSet *pRowSet, int iBatch, sqlite3_int64 iRowid){
struct RowSetEntry *p, *pTree;
/* This routine is never called after sqlite3RowSetNext() */
assert( pRowSet!=0 && (pRowSet->rsFlags & ROWSET_NEXT)==0 );
/* Sort entries into the forest on the first test of a new batch.
** To save unnecessary work, only do this when the batch number changes.
*/
if( iBatch!=pRowSet->iBatch ){ /*OPTIMIZATION-IF-FALSE*/
p = pRowSet->pEntry;
if( p ){
struct RowSetEntry **ppPrevTree = &pRowSet->pForest;
if( (pRowSet->rsFlags & ROWSET_SORTED)==0 ){ /*OPTIMIZATION-IF-FALSE*/
/* Only sort the current set of entiries if they need it */
p = rowSetEntrySort(p);
}
for(pTree = pRowSet->pForest; pTree; pTree=pTree->pRight){
ppPrevTree = &pTree->pRight;
if( pTree->pLeft==0 ){
pTree->pLeft = rowSetListToTree(p);
break;
}else{
struct RowSetEntry *pAux, *pTail;
rowSetTreeToList(pTree->pLeft, &pAux, &pTail);
pTree->pLeft = 0;
p = rowSetEntryMerge(pAux, p);
}
}
if( pTree==0 ){
*ppPrevTree = pTree = rowSetEntryAlloc(pRowSet);
if( pTree ){
pTree->v = 0;
pTree->pRight = 0;
pTree->pLeft = rowSetListToTree(p);
}
}
pRowSet->pEntry = 0;
pRowSet->pLast = 0;
pRowSet->rsFlags |= ROWSET_SORTED;
}
pRowSet->iBatch = iBatch;
}
/* Test to see if the iRowid value appears anywhere in the forest.
** Return 1 if it does and 0 if not.
*/
for(pTree = pRowSet->pForest; pTree; pTree=pTree->pRight){
p = pTree->pLeft;
while( p ){
if( p->v<iRowid ){
p = p->pRight;
}else if( p->v>iRowid ){
p = p->pLeft;
}else{
return 1;
}
}
}
return 0;
}
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