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In the BTree subsystem, when using pages from the freelist, attempt to select

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pages close to related pages in order to keep data structures near each other
in the database file.  This improves access speed in some circumstances. (CVS 667)

FossilOrigin-Name: fd7e41f0eed80fb1c7e18eb84834ec3cea74a649
This commit is contained in:
drh
2002-07-08 10:59:50 +00:00
parent 6b30867ff6
commit bea00b9a2b
3 changed files with 37 additions and 14 deletions
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37
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 1.66 2002/07/08 02:16:38 drh Exp $
** $Id: btree.c,v 1.67 2002/07/08 10:59:51 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
@ -1509,8 +1509,13 @@ int sqliteBtreeNext(BtCursor *pCur, int *pRes){
** SQLITE_OK is returned on success. Any other return value indicates
** an error. *ppPage and *pPgno are undefined in the event of an error.
** Do not invoke sqlitepager_unref() on *ppPage if an error is returned.
**
** If the "near" parameter is not 0, then a (feeble) effort is made to
** locate a page close to the page number "near". This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
*/
static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno){
static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno, Pgno near){
PageOne *pPage1 = pBt->page1;
int rc;
if( pPage1->freeList ){
@ -1533,8 +1538,23 @@ static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno){
pPage1->freeList = pOvfl->iNext;
*ppPage = (MemPage*)pOvfl;
}else{
int closest;
if( pInfo->nFree>1 && near>0 ){
int i, dist;
closest = 0;
dist = pInfo->aFree[0] - near;
if( dist<0 ) dist = -dist;
for(i=1; i<pInfo->nFree; i++){
int d2 = pInfo->aFree[i] - near;
if( d2<0 ) d2 = -d2;
if( d2<dist ) closest = i;
}
}else{
closest = 0;
}
pInfo->nFree--;
*pPgno = pInfo->aFree[pInfo->nFree];
*pPgno = pInfo->aFree[closest];
pInfo->aFree[closest] = pInfo->aFree[pInfo->nFree];
rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
sqlitepager_unref(pOvfl);
if( rc==SQLITE_OK ){
@ -1660,6 +1680,7 @@ static int fillInCell(
int nPayload;
const char *pPayload;
char *pSpace;
Pgno near = 0;
pCell->h.leftChild = 0;
pCell->h.nKey = nKey & 0xffff;
@ -1677,9 +1698,11 @@ static int fillInCell(
pPrior = 0;
while( nPayload>0 ){
if( spaceLeft==0 ){
rc = allocatePage(pBt, (MemPage**)&pOvfl, pNext);
rc = allocatePage(pBt, (MemPage**)&pOvfl, pNext, near);
if( rc ){
*pNext = 0;
}else{
near = *pNext;
}
if( pPrior ) sqlitepager_unref(pPrior);
if( rc ){
@ -1986,7 +2009,7 @@ static int balance(Btree *pBt, MemPage *pPage, BtCursor *pCur){
*/
rc = sqlitepager_write(pPage);
if( rc ) return rc;
rc = allocatePage(pBt, &pChild, &pgnoChild);
rc = allocatePage(pBt, &pChild, &pgnoChild, sqlitepager_pagenumber(pPage));
if( rc ) return rc;
assert( sqlitepager_iswriteable(pChild) );
copyPage(pChild, pPage);
@ -2171,7 +2194,7 @@ static int balance(Btree *pBt, MemPage *pPage, BtCursor *pCur){
apOld[i] = 0;
sqlitepager_write(apNew[i]);
}else{
rc = allocatePage(pBt, &apNew[i], &pgnoNew[i]);
rc = allocatePage(pBt, &apNew[i], &pgnoNew[i], pgnoNew[i-1]);
if( rc ) goto balance_cleanup;
}
nNew++;
@ -2455,7 +2478,7 @@ int sqliteBtreeCreateTable(Btree *pBt, int *piTable){
if( pBt->readOnly ){
return SQLITE_READONLY;
}
rc = allocatePage(pBt, &pRoot, &pgnoRoot);
rc = allocatePage(pBt, &pRoot, &pgnoRoot, 0);
if( rc ) return rc;
assert( sqlitepager_iswriteable(pRoot) );
zeroPage(pRoot);