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Further simplifications and improved commentting on the rowset.c module,

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including several optimization comments.

FossilOrigin-Name: 9f15a520deb9f1d4ecaa3bfff82bd57ef122aadb
This commit is contained in:
drh
2016-04-28 22:29:31 +00:00
parent 396794f0ee
commit aa50271a24
3 changed files with 30 additions and 49 deletions
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65
src/rowset.c
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@@ -57,8 +57,9 @@
** 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.
** 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"
@@ -388,59 +389,37 @@ static struct RowSetEntry *rowSetListToTree(struct RowSetEntry *pList){
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.
** 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 ) rowSetToList(p);
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 ){
if( p->pEntry==0 ){ /*OPTIMIZATION-IF-TRUE*/
/* Free memory immediately, rather than waiting on sqlite3_finalize() */
sqlite3RowSetClear(p);
}
return 1;
@@ -463,13 +442,15 @@ int sqlite3RowSetTest(RowSet *pRowSet, int iBatch, sqlite3_int64 iRowid){
/* 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
/* 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 ){
if( iBatch!=pRowSet->iBatch ){ /*OPTIMIZATION-IF-FALSE*/
p = pRowSet->pEntry;
if( p ){
struct RowSetEntry **ppPrevTree = &pRowSet->pForest;
if( (pRowSet->rsFlags & ROWSET_SORTED)==0 ){
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){