Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit7154aa1

Browse files
Fix another minor page deletion buffer lock issue.
Avoid accessing the leaf page's top parent tuple without a buffer lockheld during the second phase of nbtree page deletion. The old approachwas safe, though only because VACUUM never drops its buffer pin (andbecause only VACUUM itself can modify a half-dead page). Even still, itseems like a good idea to be strict here. Tighten things up by copyingthe top parent page's block number to a local variable before releasingthe buffer lock on the leaf page -- not after.This is a follow-up to commitfa7ff64, which fixed a similar issue inthe first phase of nbtree page deletion.Update some related comments in passing.Discussion:https://postgr.es/m/CAH2-WzkLgyN3zBvRZ1pkNJThC=xi_0gpWRUb_45eexLH1+k2_Q@mail.gmail.com
1 parentfa7ff64 commit7154aa1

File tree

1 file changed

+20
-13
lines changed

1 file changed

+20
-13
lines changed

‎src/backend/access/nbtree/nbtpage.c

Lines changed: 20 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -1951,6 +1951,7 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
19511951
*/
19521952
itemid=PageGetItemId(page,P_HIKEY);
19531953
leafhikey= (IndexTuple)PageGetItem(page,itemid);
1954+
target=BTreeTupleGetTopParent(leafhikey);
19541955
leafleftsib=opaque->btpo_prev;
19551956
leafrightsib=opaque->btpo_next;
19561957

@@ -1965,36 +1966,36 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
19651966
/*
19661967
* If the leaf page still has a parent pointing to it (or a chain of
19671968
* parents), we don't unlink the leaf page yet, but the topmost remaining
1968-
* parent in the branch. Set 'target' and 'buf' to reference the page
1969-
* actually being unlinked.
1969+
* parent in the branch (i.e. the "top parent")
19701970
*/
1971-
target=BTreeTupleGetTopParent(leafhikey);
1971+
if (!BlockNumberIsValid(target))
1972+
{
1973+
/* No top parent, so target is leaf page */
1974+
target=leafblkno;
19721975

1973-
if (target!=InvalidBlockNumber)
1976+
buf=leafbuf;
1977+
leftsib=leafleftsib;
1978+
targetlevel=0;
1979+
}
1980+
else
19741981
{
1982+
/* Target is the internal page taken from leaf's top parent */
19751983
Assert(target!=leafblkno);
19761984

1977-
/*fetch the block number of thetopmost parent's left sibling */
1985+
/*Fetch the block number of thetarget's left sibling */
19781986
buf=_bt_getbuf(rel,target,BT_READ);
19791987
page=BufferGetPage(buf);
19801988
opaque= (BTPageOpaque)PageGetSpecialPointer(page);
19811989
leftsib=opaque->btpo_prev;
19821990
targetlevel=opaque->btpo.level;
1991+
Assert(targetlevel>0);
19831992

19841993
/*
19851994
* To avoid deadlocks, we'd better drop the target page lock before
19861995
* going further.
19871996
*/
19881997
LockBuffer(buf,BUFFER_LOCK_UNLOCK);
19891998
}
1990-
else
1991-
{
1992-
target=leafblkno;
1993-
1994-
buf=leafbuf;
1995-
leftsib=leafleftsib;
1996-
targetlevel=0;
1997-
}
19981999

19992000
/*
20002001
* We have to lock the pages we need to modify in the standard order:
@@ -2181,6 +2182,12 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
21812182
* If we deleted a parent of the targeted leaf page, instead of the leaf
21822183
* itself, update the leaf to point to the next remaining child in the
21832184
* branch.
2185+
*
2186+
* Note: We rely on the fact that a buffer pin on the leaf page has been
2187+
* held since leafhikey was initialized. This is safe, though only
2188+
* because the page was already half-dead at that point. The leaf page
2189+
* cannot have been modified by any other backend during the period when
2190+
* no lock was held.
21842191
*/
21852192
if (target!=leafblkno)
21862193
BTreeTupleSetTopParent(leafhikey,nextchild);

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp