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Performance enhancement: avoid calling reparentChildPages() from balance_nonroot(). (CVS 5743)

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FossilOrigin-Name: 28fd0a50ca8529892f5b1ababd38d494889eed6d
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danielk1977
2008-09-26 17:31:55 +00:00
parent e5dd389698
commit d326064e0d
3 changed files with 55 additions and 9 deletions
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50
src/btree.c
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@@ -9,7 +9,7 @@
** May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.516 2008/09/19 16:39:38 danielk1977 Exp $
** $Id: btree.c,v 1.517 2008/09/26 17:31:55 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
@@ -5586,14 +5586,46 @@ static int balance_nonroot(MemPage *pPage){
}
/*
** Reparent children of all cells.
** At this point we used to call reparentChildPages() to make sure that
** the MemPage.pParent and MemPage.idxParent variables are correct for
** all children of the pages modified by this balance operation. Even
** if this is an auto-vacuum database there is no need to update the
** pointer-map entries for child pages - that has already been done
** by the block above.
**
** However, this is no longer necessary because the MemPage.pParent and
** MemPage.idxParent variables are only assumed to be valid when there
** are one or more references to the page (when isInit==PAGE_ISINIT_FULL).
** At this point we can account for all references to the pages
** manipulated by this function and deduce that it is not necessary to
** update these two variables because:
**
** a) it must have been called, directly or indirectly, from BtreeInsert()
** or BtreeDelete(). Both these functions call saveAllCursors(), so
** we can be sure that there exactly one write-cursor (and no
** read-cursors) open on the b-tree being manipulated. No other
** cursor may be holding references to any pages in the b-tree.
**
** b) After this function returns, the one open write-cursor will be
** moved to point at the root of the table using moveToRoot(). The
** code that does this (see BtreeInsert() and BtreeDelete()) ensures
** that the MemPage.pParent variables are not used to find the root
** page of the b-tree, it is located using BtCursor.pgnoRoot.
**
** c) the other page references are those held by this function, on
** the pages in apNew[] and apOld[]. They are about to be released.
**
** Therefore, no need to call reparentChildPages(). This can be a
** significant performance boost.
*/
#if 0
for(i=0; i<nNew; i++){
rc = reparentChildPages(apNew[i], 0);
if( rc!=SQLITE_OK ) goto balance_cleanup;
}
rc = reparentChildPages(pParent, 0);
if( rc!=SQLITE_OK ) goto balance_cleanup;
#endif
/*
** Balance the parent page. Note that the current page (pPage) might
@@ -5973,6 +6005,13 @@ int sqlite3BtreeInsert(
if( rc!=SQLITE_OK ) goto end_insert;
rc = balance(pPage, 1);
if( rc==SQLITE_OK ){
/* balance() may have messed up the chain of MemPage.pParent pointers.
** To prevent moveToRoot() from trying to use them to locate the root
** page of this table, release the reference to the current page before
** calling it.
*/
releasePage(pCur->pPage);
pCur->pPage = 0;
moveToRoot(pCur);
}
end_insert:
@@ -6089,6 +6128,13 @@ int sqlite3BtreeDelete(BtCursor *pCur){
rc = balance(pPage, 0);
}
if( rc==SQLITE_OK ){
/* balance() may have messed up the chain of MemPage.pParent pointers.
** To prevent moveToRoot() from trying to use them to locate the root
** page of this table, release the reference to the current page before
** calling it.
*/
releasePage(pCur->pPage);
pCur->pPage = 0;
moveToRoot(pCur);
}
return rc;