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提交 ef92b82d 编写于 作者: T Tom Lane
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Further cleanup in _bt_first: eliminate duplicate code paths.

上级 550d3478
隐藏空白更改
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Showing with 70 addition and 99 deletion
src/backend/access/nbtree/nbtsearch.c
浏览文件 @ ef92b82d
......@@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* 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;
bool res;
bool nextkey;
bool goback;
bool continuescan;
ScanKey scankeys;
ScanKey *startKeys = NULL;
......@@ -695,18 +696,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
pfree(startKeys);
/*
* We want to locate either the first item >= boundary point, or
* first item > boundary point, depending on the initial-positioning
* strategy we just chose.
* Examine the selected initial-positioning strategy to determine
* exactly where we need to start the scan, and set flag variables
* 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)
{
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;
goback = true;
break;
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;
goback = true;
break;
case BTEqualStrategyNumber:
......@@ -715,17 +739,41 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* equal item not first one.
*/
if (ScanDirectionIsBackward(dir))
{
/*
* This is the same as the <= strategy. We will check
* at the end whether the found item is actually =.
*/
nextkey = true;
goback = true;
}
else
{
/*
* This is the same as the >= strategy. We will check
* at the end whether the found item is actually =.
*/
nextkey = false;
goback = false;
}
break;
case BTGreaterEqualStrategyNumber:
/*
* Find first item >= scankey. (This is only used for
* forward scans.)
*/
nextkey = false;
goback = false;
break;
case BTGreaterStrategyNumber:
/*
* Find first item > scankey. (This is only used for
* forward scans.)
*/
nextkey = true;
goback = false;
break;
default:
......@@ -756,21 +804,18 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
/* remember which buffer we have pinned */
so->btso_curbuf = buf;
blkno = BufferGetBlockNumber(buf);
page = BufferGetPage(buf);
/* position to the precise item on the page */
offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey);
page = BufferGetPage(buf);
blkno = BufferGetBlockNumber(buf);
ItemPointerSet(current, blkno, offnum);
/* done with manufactured scankey, now */
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,
* 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
......@@ -781,103 +826,29 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* less than or equal to the scan key and we know that everything on
* later pages is greater than scan key.
*
* The actually desired starting point is either this item or an adjacent
* one, or in the end-of-page case it's the last item on this page or
* the first item on the next. We apply _bt_step if needed to get to
* The actually desired starting point is either this item or the prior
* one, or in the end-of-page case it's the first item on the next page
* or the last item on this page. We apply _bt_step if needed to get to
* 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
* return false.
*
* it's yet other place to add some code later for is(not)null ...
*/
switch (strat_total)
if (goback)
{
case BTLessStrategyNumber:
/*
* 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 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))
/* _bt_step will do the right thing if we are at end-of-page */
if (!_bt_step(scan, &buf, BackwardScanDirection))
return false;
}
else
{
/* If we're at end-of-page, must step forward to next page */
if (offnum > PageGetMaxOffsetNumber(page))
{
if (!_bt_step(scan, &buf, ForwardScanDirection))
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 */
......
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