src/rowset.c

   1 /*
   2 ** 2008 December 3
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 **
  13 ** This module implements an object we call a "RowSet".
  14 **
  15 ** The RowSet object is a collection of rowids.  Rowids
  16 ** are inserted into the RowSet in an arbitrary order.  Inserts
  17 ** can be intermixed with tests to see if a given rowid has been
  18 ** previously inserted into the RowSet.
  19 **
  20 ** After all inserts are finished, it is possible to extract the
  21 ** elements of the RowSet in sorted order.  Once this extraction
  22 ** process has started, no new elements may be inserted.
  23 **
  24 ** Hence, the primitive operations for a RowSet are:
  25 **
  26 **    CREATE
  27 **    INSERT
  28 **    TEST
  29 **    SMALLEST
  30 **    DESTROY
  31 **
  32 ** The CREATE and DESTROY primitives are the constructor and destructor,
  33 ** obviously.  The INSERT primitive adds a new element to the RowSet.
  34 ** TEST checks to see if an element is already in the RowSet.  SMALLEST
  35 ** extracts the least value from the RowSet.
  36 **
  37 ** The INSERT primitive might allocate additional memory.  Memory is
  38 ** allocated in chunks so most INSERTs do no allocation.  There is an
  39 ** upper bound on the size of allocated memory.  No memory is freed
  40 ** until DESTROY.
  41 **
  42 ** The TEST primitive includes a "batch" number.  The TEST primitive
  43 ** will only see elements that were inserted before the last change
  44 ** in the batch number.  In other words, if an INSERT occurs between
  45 ** two TESTs where the TESTs have the same batch nubmer, then the
  46 ** value added by the INSERT will not be visible to the second TEST.
  47 ** The initial batch number is zero, so if the very first TEST contains
  48 ** a non-zero batch number, it will see all prior INSERTs.
  49 **
  50 ** No INSERTs may occurs after a SMALLEST.  An assertion will fail if
  51 ** that is attempted.
  52 **
  53 ** The cost of an INSERT is roughly constant.  (Sometimes new memory
  54 ** has to be allocated on an INSERT.)  The cost of a TEST with a new
  55 ** batch number is O(NlogN) where N is the number of elements in the RowSet.
  56 ** The cost of a TEST using the same batch number is O(logN).  The cost
  57 ** of the first SMALLEST is O(NlogN).  Second and subsequent SMALLEST
  58 ** primitives are constant time.  The cost of DESTROY is O(N).
  59 **
  60 ** TEST and SMALLEST may not be used by the same RowSet.  This used to
  61 ** be possible, but the feature was not used, so it was removed in order
  62 ** to simplify the code.
  63 */
  64 #include "sqliteInt.h"
  65
  66
  67 /*
  68 ** Target size for allocation chunks.
  69 */
  70 #define ROWSET_ALLOCATION_SIZE 1024
  71
  72 /*
  73 ** The number of rowset entries per allocation chunk.
  74 */
  75 #define ROWSET_ENTRY_PER_CHUNK  \
  76                        ((ROWSET_ALLOCATION_SIZE-8)/sizeof(struct RowSetEntry))
  77
  78 /*
  79 ** Each entry in a RowSet is an instance of the following object.
  80 **
  81 ** This same object is reused to store a linked list of trees of RowSetEntry
  82 ** objects.  In that alternative use, pRight points to the next entry
  83 ** in the list, pLeft points to the tree, and v is unused.  The
  84 ** RowSet.pForest value points to the head of this forest list.
  85 */
  86 struct RowSetEntry {
  87   i64 v;                        /* ROWID value for this entry */
  88   struct RowSetEntry *pRight;   /* Right subtree (larger entries) or list */
  89   struct RowSetEntry *pLeft;    /* Left subtree (smaller entries) */
  90 };
  91
  92 /*
  93 ** RowSetEntry objects are allocated in large chunks (instances of the
  94 ** following structure) to reduce memory allocation overhead.  The
  95 ** chunks are kept on a linked list so that they can be deallocated
  96 ** when the RowSet is destroyed.
  97 */
  98 struct RowSetChunk {
  99   struct RowSetChunk *pNextChunk;        /* Next chunk on list of them all */
 100   struct RowSetEntry aEntry[ROWSET_ENTRY_PER_CHUNK]; /* Allocated entries */
 101 };
 102
 103 /*
 104 ** A RowSet in an instance of the following structure.
 105 **
 106 ** A typedef of this structure if found in sqliteInt.h.
 107 */
 108 struct RowSet {
 109   struct RowSetChunk *pChunk;    /* List of all chunk allocations */
 110   sqlite3 *db;                   /* The database connection */
 111   struct RowSetEntry *pEntry;    /* List of entries using pRight */
 112   struct RowSetEntry *pLast;     /* Last entry on the pEntry list */
 113   struct RowSetEntry *pFresh;    /* Source of new entry objects */
 114   struct RowSetEntry *pForest;   /* List of binary trees of entries */
 115   u16 nFresh;                    /* Number of objects on pFresh */
 116   u16 rsFlags;                   /* Various flags */
 117   int iBatch;                    /* Current insert batch */
 118 };
 119
 120 /*
 121 ** Allowed values for RowSet.rsFlags
 122 */
 123 #define ROWSET_SORTED  0x01   /* True if RowSet.pEntry is sorted */
 124 #define ROWSET_NEXT    0x02   /* True if sqlite3RowSetNext() has been called */
 125
 126 /*
 127 ** Turn bulk memory into a RowSet object.  N bytes of memory
 128 ** are available at pSpace.  The db pointer is used as a memory context
 129 ** for any subsequent allocations that need to occur.
 130 ** Return a pointer to the new RowSet object.
 131 **
 132 ** It must be the case that N is sufficient to make a Rowset.  If not
 133 ** an assertion fault occurs.
 134 **
 135 ** If N is larger than the minimum, use the surplus as an initial
 136 ** allocation of entries available to be filled.
 137 */
 138 RowSet *sqlite3RowSetInit(sqlite3 *db, void *pSpace, unsigned int N){
 139   RowSet *p;
 140   assert( N >= ROUND8(sizeof(*p)) );
 141   p = pSpace;
 142   p->pChunk = 0;
 143   p->db = db;
 144   p->pEntry = 0;
 145   p->pLast = 0;
 146   p->pForest = 0;
 147   p->pFresh = (struct RowSetEntry*)(ROUND8(sizeof(*p)) + (char*)p);
 148   p->nFresh = (u16)((N - ROUND8(sizeof(*p)))/sizeof(struct RowSetEntry));
 149   p->rsFlags = ROWSET_SORTED;
 150   p->iBatch = 0;
 151   return p;
 152 }
 153
 154 /*
 155 ** Deallocate all chunks from a RowSet.  This frees all memory that
 156 ** the RowSet has allocated over its lifetime.  This routine is
 157 ** the destructor for the RowSet.
 158 */
 159 void sqlite3RowSetClear(RowSet *p){
 160   struct RowSetChunk *pChunk, *pNextChunk;
 161   for(pChunk=p->pChunk; pChunk; pChunk = pNextChunk){
 162     pNextChunk = pChunk->pNextChunk;
 163     sqlite3DbFree(p->db, pChunk);
 164   }
 165   p->pChunk = 0;
 166   p->nFresh = 0;
 167   p->pEntry = 0;
 168   p->pLast = 0;
 169   p->pForest = 0;
 170   p->rsFlags = ROWSET_SORTED;
 171 }
 172
 173 /*
 174 ** Allocate a new RowSetEntry object that is associated with the
 175 ** given RowSet.  Return a pointer to the new and completely uninitialized
 176 ** objected.
 177 **
 178 ** In an OOM situation, the RowSet.db->mallocFailed flag is set and this
 179 ** routine returns NULL.
 180 */
 181 static struct RowSetEntry *rowSetEntryAlloc(RowSet *p){
 182   assert( p!=0 );
 183   if( p->nFresh==0 ){  /*OPTIMIZATION-IF-FALSE*/
 184     /* We could allocate a fresh RowSetEntry each time one is needed, but it
 185     ** is more efficient to pull a preallocated entry from the pool */
 186     struct RowSetChunk *pNew;
 187     pNew = sqlite3DbMallocRawNN(p->db, sizeof(*pNew));
 188     if( pNew==0 ){
 189       return 0;
 190     }
 191     pNew->pNextChunk = p->pChunk;
 192     p->pChunk = pNew;
 193     p->pFresh = pNew->aEntry;
 194     p->nFresh = ROWSET_ENTRY_PER_CHUNK;
 195   }
 196   p->nFresh--;
 197   return p->pFresh++;
 198 }
 199
 200 /*
 201 ** Insert a new value into a RowSet.
 202 **
 203 ** The mallocFailed flag of the database connection is set if a
 204 ** memory allocation fails.
 205 */
 206 void sqlite3RowSetInsert(RowSet *p, i64 rowid){
 207   struct RowSetEntry *pEntry;  /* The new entry */
 208   struct RowSetEntry *pLast;   /* The last prior entry */
 209
 210   /* This routine is never called after sqlite3RowSetNext() */
 211   assert( p!=0 && (p->rsFlags & ROWSET_NEXT)==0 );
 212
 213   pEntry = rowSetEntryAlloc(p);
 214   if( pEntry==0 ) return;
 215   pEntry->v = rowid;
 216   pEntry->pRight = 0;
 217   pLast = p->pLast;
 218   if( pLast ){
 219     if( rowid<=pLast->v ){  /*OPTIMIZATION-IF-FALSE*/
 220       /* Avoid unnecessary sorts by preserving the ROWSET_SORTED flags
 221       ** where possible */
 222       p->rsFlags &= ~ROWSET_SORTED;
 223     }
 224     pLast->pRight = pEntry;
 225   }else{
 226     p->pEntry = pEntry;
 227   }
 228   p->pLast = pEntry;
 229 }
 230
 231 /*
 232 ** Merge two lists of RowSetEntry objects.  Remove duplicates.
 233 **
 234 ** The input lists are connected via pRight pointers and are
 235 ** assumed to each already be in sorted order.
 236 */
 237 static struct RowSetEntry *rowSetEntryMerge(
 238   struct RowSetEntry *pA,    /* First sorted list to be merged */
 239   struct RowSetEntry *pB     /* Second sorted list to be merged */
 240 ){
 241   struct RowSetEntry head;
 242   struct RowSetEntry *pTail;
 243
 244   pTail = &head;
 245   assert( pA!=0 && pB!=0 );
 246   for(;;){
 247     assert( pA->pRight==0 || pA->v<=pA->pRight->v );
 248     assert( pB->pRight==0 || pB->v<=pB->pRight->v );
 249     if( pA->v<=pB->v ){
 250       if( pA->v<pB->v ) pTail = pTail->pRight = pA;
 251       pA = pA->pRight;
 252       if( pA==0 ){
 253         pTail->pRight = pB;
 254         break;
 255       }
 256     }else{
 257       pTail = pTail->pRight = pB;
 258       pB = pB->pRight;
 259       if( pB==0 ){
 260         pTail->pRight = pA;
 261         break;
 262       }
 263     }
 264   }
 265   return head.pRight;
 266 }
 267
 268 /*
 269 ** Sort all elements on the list of RowSetEntry objects into order of
 270 ** increasing v.
 271 */
 272 static struct RowSetEntry *rowSetEntrySort(struct RowSetEntry *pIn){
 273   unsigned int i;
 274   struct RowSetEntry *pNext, *aBucket[40];
 275
 276   memset(aBucket, 0, sizeof(aBucket));
 277   while( pIn ){
 278     pNext = pIn->pRight;
 279     pIn->pRight = 0;
 280     for(i=0; aBucket[i]; i++){
 281       pIn = rowSetEntryMerge(aBucket[i], pIn);
 282       aBucket[i] = 0;
 283     }
 284     aBucket[i] = pIn;
 285     pIn = pNext;
 286   }
 287   pIn = aBucket[0];
 288   for(i=1; i<sizeof(aBucket)/sizeof(aBucket[0]); i++){
 289     if( aBucket[i]==0 ) continue;
 290     pIn = pIn ? rowSetEntryMerge(pIn, aBucket[i]) : aBucket[i];
 291   }
 292   return pIn;
 293 }
 294
 295
 296 /*
 297 ** The input, pIn, is a binary tree (or subtree) of RowSetEntry objects.
 298 ** Convert this tree into a linked list connected by the pRight pointers
 299 ** and return pointers to the first and last elements of the new list.
 300 */
 301 static void rowSetTreeToList(
 302   struct RowSetEntry *pIn,         /* Root of the input tree */
 303   struct RowSetEntry **ppFirst,    /* Write head of the output list here */
 304   struct RowSetEntry **ppLast      /* Write tail of the output list here */
 305 ){
 306   assert( pIn!=0 );
 307   if( pIn->pLeft ){
 308     struct RowSetEntry *p;
 309     rowSetTreeToList(pIn->pLeft, ppFirst, &p);
 310     p->pRight = pIn;
 311   }else{
 312     *ppFirst = pIn;
 313   }
 314   if( pIn->pRight ){
 315     rowSetTreeToList(pIn->pRight, &pIn->pRight, ppLast);
 316   }else{
 317     *ppLast = pIn;
 318   }
 319   assert( (*ppLast)->pRight==0 );
 320 }
 321
 322
 323 /*
 324 ** Convert a sorted list of elements (connected by pRight) into a binary
 325 ** tree with depth of iDepth.  A depth of 1 means the tree contains a single
 326 ** node taken from the head of *ppList.  A depth of 2 means a tree with
 327 ** three nodes.  And so forth.
 328 **
 329 ** Use as many entries from the input list as required and update the
 330 ** *ppList to point to the unused elements of the list.  If the input
 331 ** list contains too few elements, then construct an incomplete tree
 332 ** and leave *ppList set to NULL.
 333 **
 334 ** Return a pointer to the root of the constructed binary tree.
 335 */
 336 static struct RowSetEntry *rowSetNDeepTree(
 337   struct RowSetEntry **ppList,
 338   int iDepth
 339 ){
 340   struct RowSetEntry *p;         /* Root of the new tree */
 341   struct RowSetEntry *pLeft;     /* Left subtree */
 342   if( *ppList==0 ){ /*OPTIMIZATION-IF-TRUE*/
 343     /* Prevent unnecessary deep recursion when we run out of entries */
 344     return 0;
 345   }
 346   if( iDepth>1 ){   /*OPTIMIZATION-IF-TRUE*/
 347     /* This branch causes a *balanced* tree to be generated.  A valid tree
 348     ** is still generated without this branch, but the tree is wildly
 349     ** unbalanced and inefficient. */
 350     pLeft = rowSetNDeepTree(ppList, iDepth-1);
 351     p = *ppList;
 352     if( p==0 ){     /*OPTIMIZATION-IF-FALSE*/
 353       /* It is safe to always return here, but the resulting tree
 354       ** would be unbalanced */
 355       return pLeft;
 356     }
 357     p->pLeft = pLeft;
 358     *ppList = p->pRight;
 359     p->pRight = rowSetNDeepTree(ppList, iDepth-1);
 360   }else{
 361     p = *ppList;
 362     *ppList = p->pRight;
 363     p->pLeft = p->pRight = 0;
 364   }
 365   return p;
 366 }
 367
 368 /*
 369 ** Convert a sorted list of elements into a binary tree. Make the tree
 370 ** as deep as it needs to be in order to contain the entire list.
 371 */
 372 static struct RowSetEntry *rowSetListToTree(struct RowSetEntry *pList){
 373   int iDepth;           /* Depth of the tree so far */
 374   struct RowSetEntry *p;       /* Current tree root */
 375   struct RowSetEntry *pLeft;   /* Left subtree */
 376
 377   assert( pList!=0 );
 378   p = pList;
 379   pList = p->pRight;
 380   p->pLeft = p->pRight = 0;
 381   for(iDepth=1; pList; iDepth++){
 382     pLeft = p;
 383     p = pList;
 384     pList = p->pRight;
 385     p->pLeft = pLeft;
 386     p->pRight = rowSetNDeepTree(&pList, iDepth);
 387   }
 388   return p;
 389 }
 390
 391 /*
 392 ** Extract the smallest element from the RowSet.
 393 ** Write the element into *pRowid.  Return 1 on success.  Return
 394 ** 0 if the RowSet is already empty.
 395 **
 396 ** After this routine has been called, the sqlite3RowSetInsert()
 397 ** routine may not be called again.
 398 **
 399 ** This routine may not be called after sqlite3RowSetTest() has
 400 ** been used.  Older versions of RowSet allowed that, but as the
 401 ** capability was not used by the code generator, it was removed
 402 ** for code economy.
 403 */
 404 int sqlite3RowSetNext(RowSet *p, i64 *pRowid){
 405   assert( p!=0 );
 406   assert( p->pForest==0 );  /* Cannot be used with sqlite3RowSetText() */
 407
 408   /* Merge the forest into a single sorted list on first call */
 409   if( (p->rsFlags & ROWSET_NEXT)==0 ){  /*OPTIMIZATION-IF-FALSE*/
 410     if( (p->rsFlags & ROWSET_SORTED)==0 ){  /*OPTIMIZATION-IF-FALSE*/
 411       p->pEntry = rowSetEntrySort(p->pEntry);
 412     }
 413     p->rsFlags |= ROWSET_SORTED|ROWSET_NEXT;
 414   }
 415
 416   /* Return the next entry on the list */
 417   if( p->pEntry ){
 418     *pRowid = p->pEntry->v;
 419     p->pEntry = p->pEntry->pRight;
 420     if( p->pEntry==0 ){ /*OPTIMIZATION-IF-TRUE*/
 421       /* Free memory immediately, rather than waiting on sqlite3_finalize() */
 422       sqlite3RowSetClear(p);
 423     }
 424     return 1;
 425   }else{
 426     return 0;
 427   }
 428 }
 429
 430 /*
 431 ** Check to see if element iRowid was inserted into the rowset as
 432 ** part of any insert batch prior to iBatch.  Return 1 or 0.
 433 **
 434 ** If this is the first test of a new batch and if there exist entries
 435 ** on pRowSet->pEntry, then sort those entries into the forest at
 436 ** pRowSet->pForest so that they can be tested.
 437 */
 438 int sqlite3RowSetTest(RowSet *pRowSet, int iBatch, sqlite3_int64 iRowid){
 439   struct RowSetEntry *p, *pTree;
 440
 441   /* This routine is never called after sqlite3RowSetNext() */
 442   assert( pRowSet!=0 && (pRowSet->rsFlags & ROWSET_NEXT)==0 );
 443
 444   /* Sort entries into the forest on the first test of a new batch.
 445   ** To save unnecessary work, only do this when the batch number changes.
 446   */
 447   if( iBatch!=pRowSet->iBatch ){  /*OPTIMIZATION-IF-FALSE*/
 448     p = pRowSet->pEntry;
 449     if( p ){
 450       struct RowSetEntry **ppPrevTree = &pRowSet->pForest;
 451       if( (pRowSet->rsFlags & ROWSET_SORTED)==0 ){ /*OPTIMIZATION-IF-FALSE*/
 452         /* Only sort the current set of entiries if they need it */
 453         p = rowSetEntrySort(p);
 454       }
 455       for(pTree = pRowSet->pForest; pTree; pTree=pTree->pRight){
 456         ppPrevTree = &pTree->pRight;
 457         if( pTree->pLeft==0 ){
 458           pTree->pLeft = rowSetListToTree(p);
 459           break;
 460         }else{
 461           struct RowSetEntry *pAux, *pTail;
 462           rowSetTreeToList(pTree->pLeft, &pAux, &pTail);
 463           pTree->pLeft = 0;
 464           p = rowSetEntryMerge(pAux, p);
 465         }
 466       }
 467       if( pTree==0 ){
 468         *ppPrevTree = pTree = rowSetEntryAlloc(pRowSet);
 469         if( pTree ){
 470           pTree->v = 0;
 471           pTree->pRight = 0;
 472           pTree->pLeft = rowSetListToTree(p);
 473         }
 474       }
 475       pRowSet->pEntry = 0;
 476       pRowSet->pLast = 0;
 477       pRowSet->rsFlags |= ROWSET_SORTED;
 478     }
 479     pRowSet->iBatch = iBatch;
 480   }
 481
 482   /* Test to see if the iRowid value appears anywhere in the forest.
 483   ** Return 1 if it does and 0 if not.
 484   */
 485   for(pTree = pRowSet->pForest; pTree; pTree=pTree->pRight){
 486     p = pTree->pLeft;
 487     while( p ){
 488       if( p->v<iRowid ){
 489         p = p->pRight;
 490       }else if( p->v>iRowid ){
 491         p = p->pLeft;
 492       }else{
 493         return 1;
 494       }
 495     }
 496   }
 497   return 0;
 498 }