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Performance improvements in getAndInitPage(): omit the upper bound check on

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page number if the page is already in cache. (CVS 5716)

FossilOrigin-Name: badd0873e6dffac9463b06a381b9f797a54d33e9
This commit is contained in:
drh
2008-09-18 01:08:15 +00:00
parent b3df2e1cfe
commit 897a820f46
3 changed files with 60 additions and 33 deletions
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79
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 1.511 2008/09/10 17:53:36 danielk1977 Exp $
** $Id: btree.c,v 1.512 2008/09/18 01:08:16 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
@@ -1051,6 +1051,21 @@ static void zeroPage(MemPage *pPage, int flags){
pPage->isInit = 1;
}
/*
** Convert a DbPage obtained from the pager into a MemPage used by
** the btree layer.
*/
static MemPage *btreePageFromDbPage(DbPage *pDbPage, Pgno pgno, BtShared *pBt){
MemPage *pPage = (MemPage*)sqlite3PagerGetExtra(pDbPage);
pPage->aData = sqlite3PagerGetData(pDbPage);
pPage->pDbPage = pDbPage;
pPage->pBt = pBt;
pPage->pgno = pgno;
pPage->hdrOffset = pPage->pgno==1 ? 100 : 0;
return pPage;
}
/*
** Get a page from the pager. Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
@@ -1069,19 +1084,12 @@ int sqlite3BtreeGetPage(
int noContent /* Do not load page content if true */
){
int rc;
MemPage *pPage;
DbPage *pDbPage;
assert( sqlite3_mutex_held(pBt->mutex) );
rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, noContent);
if( rc ) return rc;
pPage = (MemPage *)sqlite3PagerGetExtra(pDbPage);
pPage->aData = sqlite3PagerGetData(pDbPage);
pPage->pDbPage = pDbPage;
pPage->pBt = pBt;
pPage->pgno = pgno;
pPage->hdrOffset = pPage->pgno==1 ? 100 : 0;
*ppPage = pPage;
*ppPage = btreePageFromDbPage(pDbPage, pgno, pBt);
return SQLITE_OK;
}
@@ -1108,28 +1116,47 @@ static int getAndInitPage(
MemPage *pParent /* Parent of the page */
){
int rc;
DbPage *pDbPage;
MemPage *pPage;
assert( sqlite3_mutex_held(pBt->mutex) );
assert( !pParent || pParent->isInit );
if( pgno==0 || pgno>pagerPagecount(pBt->pPager) ){
if( pgno==0 ){
return SQLITE_CORRUPT_BKPT;
}
rc = sqlite3BtreeGetPage(pBt, pgno, ppPage, 0);
if( rc==SQLITE_OK ){
if( (*ppPage)->isInit==0 ){
rc = sqlite3BtreeInitPage(*ppPage, pParent);
}else if( pParent && ((*ppPage)==pParent || (*ppPage)->pParent!=pParent) ){
/* This condition indicates a loop in the b-tree structure (the scenario
** where database corruption has caused a page to be a direct or
** indirect descendant of itself).
*/
rc = SQLITE_CORRUPT_BKPT;
}
if( rc!=SQLITE_OK ){
releasePage(*ppPage);
*ppPage = 0;
}
}
/* It is often the case that the page we want is already in cache.
** If so, get it directly. This saves us from having to call
** pagerPagecount() to make sure pgno is within limits, which results
** in a measureable performance improvements.
*/
pDbPage = sqlite3PagerLookup(pBt->pPager, pgno);
if( pDbPage ){
/* Page is already in cache */
*ppPage = pPage = btreePageFromDbPage(pDbPage, pgno, pBt);
rc = SQLITE_OK;
}else{
/* Page not in cache. Acquire it. */
if( pgno>pagerPagecount(pBt->pPager) ){
return SQLITE_CORRUPT_BKPT;
}
rc = sqlite3BtreeGetPage(pBt, pgno, ppPage, 0);
if( rc ) return rc;
pPage = *ppPage;
}
if( pPage->isInit==0 ){
rc = sqlite3BtreeInitPage(pPage, pParent);
}else if( pParent && (pPage==pParent || pPage->pParent!=pParent) ){
/* This condition indicates a loop in the b-tree structure (the scenario
** where database corruption has caused a page to be a direct or
** indirect descendant of itself).
*/
rc = SQLITE_CORRUPT_BKPT;
}
if( rc!=SQLITE_OK ){
releasePage(pPage);
*ppPage = 0;
}
return rc;
}