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Comment changes only: Add several optimization marks in rowset.c. Add

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a header comment that explains what the various special comments mean.

FossilOrigin-Name: 8cdbe89ac6c22d632f677eb293111b3dbae7d6c1
This commit is contained in:
drh
2016-04-28 20:11:12 +00:00
parent 2075fb08e6
commit 396794f0ee
4 changed files with 50 additions and 16 deletions
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21
src/rowset.c
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@@ -179,7 +179,9 @@ void sqlite3RowSetClear(RowSet *p){
*/
static struct RowSetEntry *rowSetEntryAlloc(RowSet *p){
assert( p!=0 );
if( p->nFresh==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 ){
@@ -213,7 +215,9 @@ void sqlite3RowSetInsert(RowSet *p, i64 rowid){
pEntry->pRight = 0;
pLast = p->pLast;
if( pLast ){
if( (p->rsFlags & ROWSET_SORTED)!=0 && rowid<=pLast->v ){
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;
@@ -335,16 +339,19 @@ static struct RowSetEntry *rowSetNDeepTree(
){
struct RowSetEntry *p; /* Root of the new tree */
struct RowSetEntry *pLeft; /* Left subtree */
if( *ppList==0 ){
return 0;
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 it is wildly unbalanced
** and inefficient. */
** is still generated without this branch, but the tree is wildly
** unbalanced and inefficient. */
pLeft = rowSetNDeepTree(ppList, iDepth-1);
p = *ppList;
if( p==0 ){
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;