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Commit28c16f4

Browse files
Remove unnecessary PageIsEmpty() nbtree build check.
nbtree index builds cannot write out an empty page. That would meanthat there was no way to create a pivot tuple pointing to the page onelevel up, since _bt_truncate() generates one based on page's firstrighttuple.Replace the unnecessary PageIsEmpty() check with an assertion thatchecks that the page has space for at least two line pointers (thewould-be high key line pointer, plus at least one valid "data item"tuple line pointer).The PageIsEmpty() check was added by commit5d9f146 over 20 years ago.It looks like it has always been unnecessary.
1 parentf7f70d5 commit28c16f4

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1 file changed

+18
-17
lines changed

1 file changed

+18
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‎src/backend/access/nbtree/nbtsort.c‎

Lines changed: 18 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -267,7 +267,7 @@ static void _bt_build_callback(Relation index, ItemPointer tid, Datum *values,
267267
bool*isnull,booltupleIsAlive,void*state);
268268
staticPage_bt_blnewpage(uint32level);
269269
staticBTPageState*_bt_pagestate(BTWriteState*wstate,uint32level);
270-
staticvoid_bt_slideleft(Pagepage);
270+
staticvoid_bt_slideleft(Pagerightmostpage);
271271
staticvoid_bt_sortaddtup(Pagepage,Sizeitemsize,
272272
IndexTupleitup,OffsetNumberitup_off,
273273
boolnewfirstdataitem);
@@ -721,31 +721,32 @@ _bt_pagestate(BTWriteState *wstate, uint32 level)
721721
}
722722

723723
/*
724-
* slide an array of ItemIds back one slot (from P_FIRSTKEY to
725-
* P_HIKEY, overwriting P_HIKEY). we need to do this when we discover
726-
* that we have built an ItemId array in what has turned out to be a
727-
* P_RIGHTMOST page.
724+
* Slide the array of ItemIds from the page back one slot (from P_FIRSTKEY to
725+
* P_HIKEY, overwriting P_HIKEY).
726+
*
727+
* _bt_blnewpage() makes the P_HIKEY line pointer appear allocated, but the
728+
* rightmost page on its level is not supposed to get a high key. Now that
729+
* it's clear that this page is a rightmost page, remove the unneeded empty
730+
* P_HIKEY line pointer space.
728731
*/
729732
staticvoid
730-
_bt_slideleft(Pagepage)
733+
_bt_slideleft(Pagerightmostpage)
731734
{
732735
OffsetNumberoff;
733736
OffsetNumbermaxoff;
734737
ItemIdprevii;
735-
ItemIdthisii;
736738

737-
if (!PageIsEmpty(page))
739+
maxoff=PageGetMaxOffsetNumber(rightmostpage);
740+
Assert(maxoff >=P_FIRSTKEY);
741+
previi=PageGetItemId(rightmostpage,P_HIKEY);
742+
for (off=P_FIRSTKEY;off <=maxoff;off=OffsetNumberNext(off))
738743
{
739-
maxoff=PageGetMaxOffsetNumber(page);
740-
previi=PageGetItemId(page,P_HIKEY);
741-
for (off=P_FIRSTKEY;off <=maxoff;off=OffsetNumberNext(off))
742-
{
743-
thisii=PageGetItemId(page,off);
744-
*previi=*thisii;
745-
previi=thisii;
746-
}
747-
((PageHeader)page)->pd_lower-=sizeof(ItemIdData);
744+
ItemIdthisii=PageGetItemId(rightmostpage,off);
745+
746+
*previi=*thisii;
747+
previi=thisii;
748748
}
749+
((PageHeader)rightmostpage)->pd_lower-=sizeof(ItemIdData);
749750
}
750751

751752
/*

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