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Pager optimization: do not write or journal free pages. This results in

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a 2x performance gain for large INSERTs and a 5x performance gain for
large DELETEs. (CVS 410)

FossilOrigin-Name: cf1ebcfb741786f84a596c406f4c492f68cbe881
This commit is contained in:
drh
2002-03-02 20:41:57 +00:00
parent f9ffac96a7
commit 30e58750c1
5 changed files with 132 additions and 21 deletions
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80
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 1.56 2002/03/02 19:00:31 drh Exp $
** $Id: btree.c,v 1.57 2002/03/02 20:41:58 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
@@ -64,6 +64,7 @@ typedef struct Cell Cell;
typedef struct CellHdr CellHdr;
typedef struct FreeBlk FreeBlk;
typedef struct OverflowPage OverflowPage;
typedef struct FreelistInfo FreelistInfo;
/*
** All structures on a database page are aligned to 4-byte boundries.
@@ -248,6 +249,18 @@ struct OverflowPage {
char aPayload[OVERFLOW_SIZE];
};
/*
** The PageOne.freeList field points to a linked list of overflow pages
** hold information about free pages. The aPayload section of each
** overflow page contains an instance of the following structure. The
** aFree[] array holds the page number of nFree unused pages in the disk
** file.
*/
struct FreelistInfo {
int nFree;
Pgno aFree[(OVERFLOW_SIZE-sizeof(int))/sizeof(Pgno)];
};
/*
** For every page in the database file, an instance of the following structure
** is stored in memory. The u.aDisk[] array contains the raw bits read from
@@ -1477,9 +1490,11 @@ static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno){
int rc;
if( pPage1->freeList ){
OverflowPage *pOvfl;
FreelistInfo *pInfo;
rc = sqlitepager_write(pPage1);
if( rc ) return rc;
*pPgno = pPage1->freeList;
pPage1->nFree--;
rc = sqlitepager_get(pBt->pPager, pPage1->freeList, (void**)&pOvfl);
if( rc ) return rc;
rc = sqlitepager_write(pOvfl);
@@ -1487,9 +1502,21 @@ static int allocatePage(Btree *pBt, MemPage **ppPage, Pgno *pPgno){
sqlitepager_unref(pOvfl);
return rc;
}
pPage1->freeList = pOvfl->iNext;
pPage1->nFree--;
*ppPage = (MemPage*)pOvfl;
pInfo = (FreelistInfo*)pOvfl->aPayload;
if( pInfo->nFree==0 ){
*pPgno = pPage1->freeList;
pPage1->freeList = pOvfl->iNext;
*ppPage = (MemPage*)pOvfl;
}else{
pInfo->nFree--;
*pPgno = pInfo->aFree[pInfo->nFree];
rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
sqlitepager_unref(pOvfl);
if( rc==SQLITE_OK ){
sqlitepager_dont_rollback(*ppPage);
rc = sqlitepager_write(*ppPage);
}
}
}else{
*pPgno = sqlitepager_pagecount(pBt->pPager) + 1;
rc = sqlitepager_get(pBt->pPager, *pPgno, (void**)ppPage);
@@ -1521,6 +1548,25 @@ static int freePage(Btree *pBt, void *pPage, Pgno pgno){
if( rc ){
return rc;
}
pPage1->nFree++;
if( pPage1->nFree>0 && pPage1->freeList ){
OverflowPage *pFreeIdx;
rc = sqlitepager_get(pBt->pPager, pPage1->freeList, (void**)&pFreeIdx);
if( rc==SQLITE_OK ){
FreelistInfo *pInfo = (FreelistInfo*)pFreeIdx->aPayload;
if( pInfo->nFree<(sizeof(pInfo->aFree)/sizeof(pInfo->aFree[0])) ){
rc = sqlitepager_write(pFreeIdx);
if( rc==SQLITE_OK ){
pInfo->aFree[pInfo->nFree] = pgno;
pInfo->nFree++;
sqlitepager_unref(pFreeIdx);
sqlitepager_dont_write(pBt->pPager, pgno);
return rc;
}
}
sqlitepager_unref(pFreeIdx);
}
}
if( pOvfl==0 ){
assert( pgno>0 );
rc = sqlitepager_get(pBt->pPager, pgno, (void**)&pOvfl);
@@ -1534,7 +1580,6 @@ static int freePage(Btree *pBt, void *pPage, Pgno pgno){
}
pOvfl->iNext = pPage1->freeList;
pPage1->freeList = pgno;
pPage1->nFree++;
memset(pOvfl->aPayload, 0, OVERFLOW_SIZE);
pMemPage = (MemPage*)pPage;
pMemPage->isInit = 0;
@@ -2703,9 +2748,16 @@ static int checkRef(IntegrityCk *pCheck, int iPage, char *zContext){
** Check the integrity of the freelist or of an overflow page list.
** Verify that the number of pages on the list is N.
*/
static void checkList(IntegrityCk *pCheck, int iPage, int N, char *zContext){
static void checkList(
IntegrityCk *pCheck, /* Integrity checking context */
int isFreeList, /* True for a freelist. False for overflow page list */
int iPage, /* Page number for first page in the list */
int N, /* Expected number of pages in the list */
char *zContext /* Context for error messages */
){
int i;
char zMsg[100];
while( N-- ){
while( N-- > 0 ){
OverflowPage *pOvfl;
if( iPage<1 ){
sprintf(zMsg, "%d pages missing from overflow list", N+1);
@@ -2718,6 +2770,13 @@ static void checkList(IntegrityCk *pCheck, int iPage, int N, char *zContext){
checkAppendMsg(pCheck, zContext, zMsg);
break;
}
if( isFreeList ){
FreelistInfo *pInfo = (FreelistInfo*)pOvfl->aPayload;
for(i=0; i<pInfo->nFree; i++){
checkRef(pCheck, pInfo->aFree[i], zMsg);
}
N -= pInfo->nFree;
}
iPage = (int)pOvfl->iNext;
sqlitepager_unref(pOvfl);
}
@@ -2818,7 +2877,7 @@ static int checkTreePage(
sprintf(zContext, "On page %d cell %d: ", iPage, i);
if( sz>MX_LOCAL_PAYLOAD ){
int nPage = (sz - MX_LOCAL_PAYLOAD + OVERFLOW_SIZE - 1)/OVERFLOW_SIZE;
checkList(pCheck, pCell->ovfl, nPage, zContext);
checkList(pCheck, 0, pCell->ovfl, nPage, zContext);
}
/* Check that keys are in the right order
@@ -2923,7 +2982,8 @@ char *sqliteBtreeIntegrityCheck(Btree *pBt, int *aRoot, int nRoot){
/* Check the integrity of the freelist
*/
checkList(&sCheck, pBt->page1->freeList, pBt->page1->nFree,"Main freelist: ");
checkList(&sCheck, 1, pBt->page1->freeList, pBt->page1->nFree,
"Main freelist: ");
/* Check all the tables.
*/