int itemIndex;
bool continuescan;
int indnatts;
- bool requiredMatchedByPrecheck;
+ bool continuescanPrechecked;
+ bool haveFirstMatch = false;
/*
* We must have the buffer pinned and locked, but the usual macro can't be
Assert(BTScanPosIsPinned(so->currPos));
/*
- * Prechecking the page with scan keys required for direction scan. We
- * check these keys with the last item on the page (according to our scan
- * direction). If these keys are matched, we can skip checking them with
- * every item on the page. Scan keys for our scan direction would
- * necessarily match the previous items. Scan keys required for opposite
- * direction scan are already matched by the _bt_first() call.
+ * Prechecking the value of the continuescan flag for the last item on the
+ * page (for backwards scan it will be the first item on a page). If we
+ * observe it to be true, then it should be true for all other items. This
+ * allows us to do significant optimizations in the _bt_checkkeys()
+ * function for all the items on the page.
*
* With the forward scan, we do this check for the last item on the page
* instead of the high key. It's relatively likely that the most
itup = (IndexTuple) PageGetItem(page, iid);
/*
- * Do the precheck. Note that we pass the pointer to
- * 'requiredMatchedByPrecheck' to 'continuescan' argument. That will
+ * Do the precheck. Note that we pass the pointer to the
+ * 'continuescanPrechecked' to the 'continuescan' argument. That will
* set flag to true if all required keys are satisfied and false
* otherwise.
*/
(void) _bt_checkkeys(scan, itup, indnatts, dir,
- &requiredMatchedByPrecheck, false);
+ &continuescanPrechecked, false, false);
}
else
{
- requiredMatchedByPrecheck = false;
+ continuescanPrechecked = false;
}
if (ScanDirectionIsForward(dir))
Assert(!BTreeTupleIsPivot(itup));
passes_quals = _bt_checkkeys(scan, itup, indnatts, dir,
- &continuescan, requiredMatchedByPrecheck);
+ &continuescan,
+ continuescanPrechecked,
+ haveFirstMatch);
/*
* If the result of prechecking required keys was true, then in
* assert-enabled builds we also recheck that the _bt_checkkeys()
* result is the same.
*/
- Assert(!requiredMatchedByPrecheck ||
+ Assert((!continuescanPrechecked && haveFirstMatch) ||
passes_quals == _bt_checkkeys(scan, itup, indnatts, dir,
- &continuescan, false));
+ &continuescan, false, false));
if (passes_quals)
{
/* tuple passes all scan key conditions */
+ haveFirstMatch = true;
if (!BTreeTupleIsPosting(itup))
{
/* Remember it */
int truncatt;
truncatt = BTreeTupleGetNAtts(itup, scan->indexRelation);
- _bt_checkkeys(scan, itup, truncatt, dir, &continuescan, false);
+ _bt_checkkeys(scan, itup, truncatt, dir, &continuescan, false, false);
}
if (!continuescan)
Assert(!BTreeTupleIsPivot(itup));
passes_quals = _bt_checkkeys(scan, itup, indnatts, dir,
- &continuescan, requiredMatchedByPrecheck);
+ &continuescan,
+ continuescanPrechecked,
+ haveFirstMatch);
/*
* If the result of prechecking required keys was true, then in
* assert-enabled builds we also recheck that the _bt_checkkeys()
* result is the same.
*/
- Assert(!requiredMatchedByPrecheck ||
+ Assert((!continuescanPrechecked && !haveFirstMatch) ||
passes_quals == _bt_checkkeys(scan, itup, indnatts, dir,
- &continuescan, false));
+ &continuescan, false, false));
if (passes_quals && tuple_alive)
{
/* tuple passes all scan key conditions */
+ haveFirstMatch = true;
if (!BTreeTupleIsPosting(itup))
{
/* Remember it */
* tupnatts: number of attributes in tupnatts (high key may be truncated)
* dir: direction we are scanning in
* continuescan: output parameter (will be set correctly in all cases)
- * requiredMatchedByPrecheck: indicates that scan keys required for
- * direction scan are already matched
+ * continuescanPrechecked: indicates that *continuescan flag is known to
+ * be true for the last item on the page
+ * haveFirstMatch: indicates that we already have at least one match
+ * in the current page
*/
bool
_bt_checkkeys(IndexScanDesc scan, IndexTuple tuple, int tupnatts,
ScanDirection dir, bool *continuescan,
- bool requiredMatchedByPrecheck)
+ bool continuescanPrechecked, bool haveFirstMatch)
{
TupleDesc tupdesc;
BTScanOpaque so;
requiredOppositeDir = true;
/*
- * Is the key required for scanning for either forward or backward
- * direction? If so and caller told us that these types of keys are
- * known to be matched, skip the check. Except for the row keys,
- * where NULLs could be found in the middle of matching values.
+ * If the caller told us the *continuescan flag is known to be true
+ * for the last item on the page, then we know the keys required for
+ * the current direction scan should be matched. Otherwise, the
+ * *continuescan flag would be set for the current item and
+ * subsequently the last item on the page accordingly.
+ *
+ * If the key is required for the opposite direction scan, we can skip
+ * the check if the caller tells us there was already at least one
+ * matching item on the page. Also, we require the *continuescan flag
+ * to be true for the last item on the page to know there are no
+ * NULLs.
+ *
+ * Both cases above work except for the row keys, where NULLs could be
+ * found in the middle of matching values.
*/
- if ((requiredSameDir || requiredOppositeDir) &&
- !(key->sk_flags & SK_ROW_HEADER) && requiredMatchedByPrecheck)
+ if ((requiredSameDir || (requiredOppositeDir && haveFirstMatch)) &&
+ !(key->sk_flags & SK_ROW_HEADER) && continuescanPrechecked)
continue;
if (key->sk_attno > tupnatts)
}
/*
- * Apply the key checking function. When the key is required for
- * opposite direction scan, it must be already satisfied by
- * _bt_first() except for the NULLs checking, which have already done
- * above.
+ * Apply the key-checking function. When the key is required for the
+ * opposite direction scan, it must be already satisfied as soon as
+ * there is already match on the page. Except for the NULLs checking,
+ * which have already done above.
*/
- if (!requiredOppositeDir)
+ if (!(requiredOppositeDir && haveFirstMatch))
{
test = FunctionCall2Coll(&key->sk_func, key->sk_collation,
datum, key->sk_argument);
projects / postgresql.git / commitdiff