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Further cleanup in _bt_first: eliminate duplicate code paths.

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This commit is contained in:
Tom Lane 2003-12-21 17:52:34 +00:00
parent 550d347811
commit ef92b82dbb
1 changed files with 70 additions and 99 deletions
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169
src/backend/access/nbtree/nbtsearch.c
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@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.85 2003/12/21 03:00:04 tgl Exp $ * $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.86 2003/12/21 17:52:34 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -496,6 +496,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
StrategyNumber strat; StrategyNumber strat;
bool res; bool res;
bool nextkey; bool nextkey;
bool goback;
bool continuescan; bool continuescan;
ScanKey scankeys; ScanKey scankeys;
ScanKey *startKeys = NULL; ScanKey *startKeys = NULL;
@ -695,18 +696,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
pfree(startKeys); pfree(startKeys);
/* /*
* We want to locate either the first item >= boundary point, or * Examine the selected initial-positioning strategy to determine
* first item > boundary point, depending on the initial-positioning * exactly where we need to start the scan, and set flag variables
* strategy we just chose. * to control the code below.
*
* If nextkey = false, _bt_search and _bt_binsrch will locate the
* first item >= scan key. If nextkey = true, they will locate the
* first item > scan key.
*
* If goback = true, we will then step back one item, while if
* goback = false, we will start the scan on the located item.
*
* it's yet other place to add some code later for is(not)null ...
*/ */
switch (strat_total) switch (strat_total)
{ {
case BTLessStrategyNumber: case BTLessStrategyNumber:
/*
* Find first item >= scankey, then back up one to arrive at last
* item < scankey. (Note: this positioning strategy is only used
* for a backward scan, so that is always the correct starting
* position.)
*/
nextkey = false; nextkey = false;
goback = true;
break; break;
case BTLessEqualStrategyNumber: case BTLessEqualStrategyNumber:
/*
* Find first item > scankey, then back up one to arrive at last
* item <= scankey. (Note: this positioning strategy is only used
* for a backward scan, so that is always the correct starting
* position.)
*/
nextkey = true; nextkey = true;
goback = true;
break; break;
case BTEqualStrategyNumber: case BTEqualStrategyNumber:
@ -715,17 +739,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* equal item not first one. * equal item not first one.
*/ */
if (ScanDirectionIsBackward(dir)) if (ScanDirectionIsBackward(dir))
{
/*
* This is the same as the <= strategy. We will check
* at the end whether the found item is actually =.
*/
nextkey = true; nextkey = true;
goback = true;
}
else else
{
/*
* This is the same as the >= strategy. We will check
* at the end whether the found item is actually =.
*/
nextkey = false; nextkey = false;
goback = false;
}
break; break;
case BTGreaterEqualStrategyNumber: case BTGreaterEqualStrategyNumber:
/*
* Find first item >= scankey. (This is only used for
* forward scans.)
*/
nextkey = false; nextkey = false;
goback = false;
break; break;
case BTGreaterStrategyNumber: case BTGreaterStrategyNumber:
/*
* Find first item > scankey. (This is only used for
* forward scans.)
*/
nextkey = true; nextkey = true;
goback = false;
break; break;
default: default:
@ -756,21 +804,18 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
/* remember which buffer we have pinned */ /* remember which buffer we have pinned */
so->btso_curbuf = buf; so->btso_curbuf = buf;
blkno = BufferGetBlockNumber(buf);
page = BufferGetPage(buf);
/* position to the precise item on the page */ /* position to the precise item on the page */
offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey); offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey);
page = BufferGetPage(buf);
blkno = BufferGetBlockNumber(buf);
ItemPointerSet(current, blkno, offnum); ItemPointerSet(current, blkno, offnum);
/* done with manufactured scankey, now */ /* done with manufactured scankey, now */
pfree(scankeys); pfree(scankeys);
/* /*
* It's now time to examine the initial-positioning strategy to find the
* exact place to start the scan.
*
* If nextkey = false, we are positioned at the first item >= scan key, * If nextkey = false, we are positioned at the first item >= scan key,
* or possibly at the end of a page on which all the existing items are * or possibly at the end of a page on which all the existing items are
* less than the scan key and we know that everything on later pages * less than the scan key and we know that everything on later pages
@ -781,103 +826,29 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* less than or equal to the scan key and we know that everything on * less than or equal to the scan key and we know that everything on
* later pages is greater than scan key. * later pages is greater than scan key.
* *
* The actually desired starting point is either this item or an adjacent * The actually desired starting point is either this item or the prior
* one, or in the end-of-page case it's the last item on this page or * one, or in the end-of-page case it's the first item on the next page
* the first item on the next. We apply _bt_step if needed to get to * or the last item on this page. We apply _bt_step if needed to get to
* the right place. * the right place.
* *
* Note: if _bt_step fails (meaning we fell off the end of the index in * If _bt_step fails (meaning we fell off the end of the index in
* one direction or the other), then there are no matches so we just * one direction or the other), then there are no matches so we just
* return false. * return false.
*
* it's yet other place to add some code later for is(not)null ...
*/ */
switch (strat_total) if (goback)
{ {
case BTLessStrategyNumber: /* _bt_step will do the right thing if we are at end-of-page */
if (!_bt_step(scan, &buf, BackwardScanDirection))
/* return false;
* We are on first item >= scankey. }
* else
* Back up one to arrive at last item < scankey. (Note: this {
* positioning strategy is only used for a backward scan, so /* If we're at end-of-page, must step forward to next page */
* that is always the correct starting position.) if (offnum > PageGetMaxOffsetNumber(page))
*/ {
if (!_bt_step(scan, &buf, BackwardScanDirection)) if (!_bt_step(scan, &buf, ForwardScanDirection))
return false; return false;
break; }
case BTLessEqualStrategyNumber:
/*
* We are on first item > scankey.
*
* Back up one to arrive at last item <= scankey. (Note: this
* positioning strategy is only used for a backward scan, so
* that is always the correct starting position.)
*/
if (!_bt_step(scan, &buf, BackwardScanDirection))
return false;
break;
case BTEqualStrategyNumber:
/*
* If a backward scan was specified, need to start with last
* equal item not first one.
*/
if (ScanDirectionIsBackward(dir))
{
/*
* We are on first item > scankey.
*
* Back up one to arrive at last item <= scankey.
* We will check below to see if it is equal to scankey.
*/
if (!_bt_step(scan, &buf, BackwardScanDirection))
return false;
}
else
{
/*
* We are on first item >= scankey.
*
* Make sure we are on a real item; might have to
* step forward if currently at end of page.
* We will check below to see if it is equal to scankey.
*/
if (offnum > PageGetMaxOffsetNumber(page))
{
if (!_bt_step(scan, &buf, ForwardScanDirection))
return false;
}
}
break;
case BTGreaterEqualStrategyNumber:
/*
* We want the first item >= scankey, which is where we are...
* unless we're not anywhere at all...
*/
if (offnum > PageGetMaxOffsetNumber(page))
{
if (!_bt_step(scan, &buf, ForwardScanDirection))
return false;
}
break;
case BTGreaterStrategyNumber:
/*
* We want the first item > scankey, which is where we are...
* unless we're not anywhere at all...
*/
if (offnum > PageGetMaxOffsetNumber(page))
{
if (!_bt_step(scan, &buf, ForwardScanDirection))
return false;
}
break;
} }
/* okay, current item pointer for the scan is right */ /* okay, current item pointer for the scan is right */