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Overview
Comment:Further simplifications and improved commentting on the rowset.c module, including several optimization comments.
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SHA1:9f15a520deb9f1d4ecaa3bfff82bd57ef122aadb
User & Date: drh 2016-04-28 22:29:31
Context
2016-04-29
02:55
Some optimization comments added to vdbe.c. No functional changes to code. check-in: e7c22e3b user: drh tags: trunk
2016-04-28
22:29
Further simplifications and improved commentting on the rowset.c module, including several optimization comments. check-in: 9f15a520 user: drh tags: trunk
20:11
Comment changes only: Add several optimization marks in rowset.c. Add a header comment that explains what the various special comments mean. check-in: 8cdbe89a user: drh tags: trunk
Changes
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Changes to src/rowset.c.

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** 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).
**
** There is an added cost of O(N) when switching between TEST and
** SMALLEST primitives.

*/
#include "sqliteInt.h"


/*
** Target size for allocation chunks.
*/
................................................................................
    pList = p->pRight;
    p->pLeft = pLeft;
    p->pRight = rowSetNDeepTree(&pList, iDepth);
  }
  return p;
}

/*
** Take all the entries on p->pEntry and on the trees in p->pForest and
** sort them all together into one big ordered list on p->pEntry.
**
** This routine should only be called once in the life of a RowSet.
*/
static void rowSetToList(RowSet *p){

  /* This routine is called only once */
  assert( p!=0 && (p->rsFlags & ROWSET_NEXT)==0 );

  if( (p->rsFlags & ROWSET_SORTED)==0 ){
    p->pEntry = rowSetEntrySort(p->pEntry);
  }

  /* While this module could theoretically support it, sqlite3RowSetNext()
  ** is never called after sqlite3RowSetText() for the same RowSet.  So
  ** there is never a forest to deal with.  Should this change, simply
  ** remove the assert() and the #if 0. */
  assert( p->pForest==0 );
#if 0
  while( p->pForest ){
    struct RowSetEntry *pTree = p->pForest->pLeft;
    if( pTree ){
      struct RowSetEntry *pHead, *pTail;
      rowSetTreeToList(pTree, &pHead, &pTail);
      p->pEntry = rowSetEntryMerge(p->pEntry, pHead);
    }
    p->pForest = p->pForest->pRight;
  }
#endif
  p->rsFlags |= ROWSET_NEXT;  /* Verify this routine is never called again */
}

/*
** 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.  





*/
int sqlite3RowSetNext(RowSet *p, i64 *pRowid){
  assert( p!=0 );


  /* Merge the forest into a single sorted list on first call */
  if( (p->rsFlags & ROWSET_NEXT)==0 ) rowSetToList(p);






  /* Return the next entry on the list */
  if( p->pEntry ){
    *pRowid = p->pEntry->v;
    p->pEntry = p->pEntry->pRight;
    if( p->pEntry==0 ){

      sqlite3RowSetClear(p);
    }
    return 1;
  }else{
    return 0;
  }
}
................................................................................
*/
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 

  */
  if( iBatch!=pRowSet->iBatch ){
    p = pRowSet->pEntry;
    if( p ){
      struct RowSetEntry **ppPrevTree = &pRowSet->pForest;
      if( (pRowSet->rsFlags & ROWSET_SORTED)==0 ){

        p = rowSetEntrySort(p);
      }
      for(pTree = pRowSet->pForest; pTree; pTree=pTree->pRight){
        ppPrevTree = &pTree->pRight;
        if( pTree->pLeft==0 ){
          pTree->pLeft = rowSetListToTree(p);
          break;







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** 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.
*/
................................................................................
    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;
  }
}
................................................................................
*/
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;