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Remove block number field from nbtree stack.

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The initial value of the nbtree stack downlink block number field
recorded during an initial descent of the tree wasn't actually used.
Both _bt_getstackbuf() callers overwrote the value with their own value.

Remove the block number field from the stack struct, and add a child
block number argument to _bt_getstackbuf() in its place.  This makes the
overall design of _bt_getstackbuf() clearer.

Author: Peter Geoghegan
Reviewed-By: Anastasia Lubennikova
Discussion: https://postgr.es/m/CAH2-Wzmx+UbXt2YNOUCZ-a04VdXU=S=OHuAuD7Z8uQq-PXTYUg@mail.gmail.com
This commit is contained in:
Peter Geoghegan
2019-08-14 11:32:35 -07:00
parent fded4773eb
commit 9c02cf5661
5 changed files with 50 additions and 42 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
src/backend/access/nbtree/nbtinsert.c
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@@ -1797,7 +1797,6 @@ _bt_insert_parent(Relation rel,
stack = &fakestack;
stack->bts_blkno = BufferGetBlockNumber(pbuf);
stack->bts_offset = InvalidOffsetNumber;
stack->bts_btentry = InvalidBlockNumber;
stack->bts_parent = NULL;
_bt_relbuf(rel, pbuf);
}
@@ -1819,8 +1818,7 @@ _bt_insert_parent(Relation rel,
* new downlink will be inserted at the correct offset. Even buf's
* parent may have changed.
*/
stack->bts_btentry = bknum;
pbuf = _bt_getstackbuf(rel, stack);
pbuf = _bt_getstackbuf(rel, stack, bknum);
/*
* Now we can unlock the right child. The left child will be unlocked
@@ -1834,7 +1832,7 @@ _bt_insert_parent(Relation rel,
errmsg_internal("failed to re-find parent key in index \"%s\" for split pages %u/%u",
RelationGetRelationName(rel), bknum, rbknum)));
/* Recursively update the parent */
/* Recursively insert into the parent */
_bt_insertonpg(rel, NULL, pbuf, buf, stack->bts_parent,
new_item, stack->bts_offset + 1,
is_only);
@@ -1901,21 +1899,37 @@ _bt_finish_split(Relation rel, Buffer lbuf, BTStack stack)
}
/*
* _bt_getstackbuf() -- Walk back up the tree one step, and find the item
* we last looked at in the parent.
* _bt_getstackbuf() -- Walk back up the tree one step, and find the pivot
* tuple whose downlink points to child page.
*
* This is possible because we save the downlink from the parent item,
* which is enough to uniquely identify it. Insertions into the parent
* level could cause the item to move right; deletions could cause it
* to move left, but not left of the page we previously found it in.
* Caller passes child's block number, which is used to identify
* associated pivot tuple in parent page using a linear search that
* matches on pivot's downlink/block number. The expected location of
* the pivot tuple is taken from the stack one level above the child
* page. This is used as a starting point. Insertions into the
* parent level could cause the pivot tuple to move right; deletions
* could cause it to move left, but not left of the page we previously
* found it on.
*
* Adjusts bts_blkno & bts_offset if changed.
* Caller can use its stack to relocate the pivot tuple/downlink for
* any same-level page to the right of the page found by its initial
* descent. This is necessary because of the possibility that caller
* moved right to recover from a concurrent page split. It's also
* convenient for certain callers to be able to step right when there
* wasn't a concurrent page split, while still using their original
* stack. For example, the checkingunique _bt_doinsert() case may
* have to step right when there are many physical duplicates, and its
* scantid forces an insertion to the right of the "first page the
* value could be on".
*
* Returns write-locked buffer, or InvalidBuffer if item not found
* (should not happen).
* Returns write-locked parent page buffer, or InvalidBuffer if pivot
* tuple not found (should not happen). Adjusts bts_blkno &
* bts_offset if changed. Page split caller should insert its new
* pivot tuple for its new right sibling page on parent page, at the
* offset number bts_offset + 1.
*/
Buffer
_bt_getstackbuf(Relation rel, BTStack stack)
_bt_getstackbuf(Relation rel, BTStack stack, BlockNumber child)
{
BlockNumber blkno;
OffsetNumber start;
@@ -1977,7 +1991,7 @@ _bt_getstackbuf(Relation rel, BTStack stack)
itemid = PageGetItemId(page, offnum);
item = (IndexTuple) PageGetItem(page, itemid);
if (BTreeInnerTupleGetDownLink(item) == stack->bts_btentry)
if (BTreeInnerTupleGetDownLink(item) == child)
{
/* Return accurate pointer to where link is now */
stack->bts_blkno = blkno;
@@ -1993,7 +2007,7 @@ _bt_getstackbuf(Relation rel, BTStack stack)
itemid = PageGetItemId(page, offnum);
item = (IndexTuple) PageGetItem(page, itemid);
if (BTreeInnerTupleGetDownLink(item) == stack->bts_btentry)
if (BTreeInnerTupleGetDownLink(item) == child)
{
/* Return accurate pointer to where link is now */
stack->bts_blkno = blkno;