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-rw-r--r-- | src/rowset.c | 502 |
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diff --git a/src/rowset.c b/src/rowset.c new file mode 100644 index 0000000..5956cb2 --- /dev/null +++ b/src/rowset.c @@ -0,0 +1,502 @@ +/* +** 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 number, 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 +** object. +** +** 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 entries 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; +} |