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Two optimizations to the pager: (1) Write dirty pages back to the database

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file in order and (2) Keep a separate list of in-memory pages that are in
the checkpoint journal in order to speed a checkpoint commit. (CVS 783)

FossilOrigin-Name: a6ef6657a4377684dc2fce7be2bbf009fd2d2f37
This commit is contained in:
drh
2002-11-10 23:32:56 +00:00
parent 8766c34348
commit 03eb96a7b2
3 changed files with 161 additions and 21 deletions
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168
src/pager.c
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@@ -18,7 +18,7 @@
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.56 2002/11/09 00:33:16 drh Exp $
** @(#) $Id: pager.c,v 1.57 2002/11/10 23:32:57 drh Exp $
*/
#include "os.h" /* Must be first to enable large file support */
#include "sqliteInt.h"
@@ -74,6 +74,8 @@ struct PgHdr {
int nRef; /* Number of users of this page */
PgHdr *pNextFree, *pPrevFree; /* Freelist of pages where nRef==0 */
PgHdr *pNextAll, *pPrevAll; /* A list of all pages */
PgHdr *pNextCkpt, *pPrevCkpt; /* List of pages in the checkpoint journal */
PgHdr *pSort; /* Next in list of pages to be written */
u8 inJournal; /* TRUE if has been written to journal */
u8 inCkpt; /* TRUE if written to the checkpoint journal */
u8 dirty; /* TRUE if we need to write back changes */
@@ -130,6 +132,7 @@ struct Pager {
u8 *aInCkpt; /* One bit for each page in the database */
PgHdr *pFirst, *pLast; /* List of free pages */
PgHdr *pAll; /* List of all pages */
PgHdr *pCkpt; /* List of pages in the checkpoint journal */
PgHdr *aHash[N_PG_HASH]; /* Hash table to map page number of PgHdr */
};
@@ -253,6 +256,45 @@ static int pager_errcode(Pager *pPager){
return rc;
}
/*
** Add or remove a page from the list of all pages that are in the
** checkpoint journal.
**
** The Pager keeps a separate list of pages that are currently in
** the checkpoint journal. This helps the sqlitepager_ckpt_commit()
** routine run MUCH faster for the common case where there are many
** pages in memory but only a few are in the checkpoint journal.
*/
static void page_add_to_ckpt_list(PgHdr *pPg){
Pager *pPager = pPg->pPager;
if( pPg->inCkpt ) return;
assert( pPg->pPrevCkpt==0 && pPg->pNextCkpt==0 );
pPg->pPrevCkpt = 0;
if( pPager->pCkpt ){
pPager->pCkpt->pPrevCkpt = pPg;
}
pPg->pNextCkpt = pPager->pCkpt;
pPager->pCkpt = pPg;
pPg->inCkpt = 1;
}
static void page_remove_from_ckpt_list(PgHdr *pPg){
if( !pPg->inCkpt ) return;
if( pPg->pPrevCkpt ){
assert( pPg->pPrevCkpt->pNextCkpt==pPg );
pPg->pPrevCkpt->pNextCkpt = pPg->pNextCkpt;
}else{
assert( pPg->pPager->pCkpt==pPg );
pPg->pPager->pCkpt = pPg->pNextCkpt;
}
if( pPg->pNextCkpt ){
assert( pPg->pNextCkpt->pPrevCkpt==pPg );
pPg->pNextCkpt->pPrevCkpt = pPg->pPrevCkpt;
}
pPg->pNextCkpt = 0;
pPg->pPrevCkpt = 0;
pPg->inCkpt = 0;
}
/*
** Find a page in the hash table given its page number. Return
** a pointer to the page or NULL if not found.
@@ -752,6 +794,41 @@ int sqlitepager_ref(void *pData){
return SQLITE_OK;
}
/*
** The parameters are pointers to the head of two sorted lists
** of page headers. Merge these two lists together and return
** a single sorted list. This routine forms the core of the
** merge-sort algorithm that sorts dirty pages into accending
** order prior to writing them back to the disk.
**
** In the case of a tie, left sorts in front of right.
**
** Headers are sorted in order of ascending page number.
*/
static PgHdr *page_merge(PgHdr *pLeft, PgHdr *pRight){
PgHdr sHead;
PgHdr *pTail;
pTail = &sHead;
pTail->pSort = 0;
while( pLeft && pRight ){
if( pLeft->pgno<=pRight->pgno ){
pTail->pSort = pLeft;
pLeft = pLeft->pSort;
}else{
pTail->pSort = pRight;
pRight = pRight->pSort;
}
pTail = pTail->pSort;
}
if( pLeft ){
pTail->pSort = pLeft;
}else if( pRight ){
pTail->pSort = pRight;
}
return sHead.pSort;
}
/*
** Sync the journal and then write all free dirty pages to the database
** file.
@@ -768,10 +845,24 @@ int sqlitepager_ref(void *pData){
** If we are writing to temporary database, there is no need to preserve
** the integrity of the journal file, so we can save time and skip the
** fsync().
**
** This routine goes to the extra trouble of sorting all the dirty
** pages by their page number prior to writing them. Tests show that
** writing pages in order by page number gives a modest speed improvement
** under Linux.
*/
static int syncAllPages(Pager *pPager){
PgHdr *pPg;
PgHdr *pToWrite;
# define NSORT 28
Pgno lastPgno;
int i;
PgHdr *apSorter[NSORT];
int rc = SQLITE_OK;
/* Sync the journal before modifying the main database
** (assuming there is a journal and it needs to be synced.)
*/
if( pPager->needSync ){
if( !pPager->tempFile ){
rc = sqliteOsSync(&pPager->jfd);
@@ -779,14 +870,58 @@ static int syncAllPages(Pager *pPager){
}
pPager->needSync = 0;
}
/* Create a list of all dirty pages
*/
pToWrite = 0;
for(pPg=pPager->pFirst; pPg; pPg=pPg->pNextFree){
if( pPg->dirty ){
sqliteOsSeek(&pPager->fd, (pPg->pgno-1)*SQLITE_PAGE_SIZE);
rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ) break;
pPg->dirty = 0;
pPg->pSort = pToWrite;
pToWrite = pPg;
}
}
/* Sort the list of dirty pages into accending order by
** page number
*/
for(i=0; i<NSORT; i++){
apSorter[i] = 0;
}
while( pToWrite ){
pPg = pToWrite;
pToWrite = pPg->pSort;
pPg->pSort = 0;
for(i=0; i<NSORT-1; i++){
if( apSorter[i]==0 ){
apSorter[i] = pPg;
break;
}else{
pPg = page_merge(apSorter[i], pPg);
apSorter[i] = 0;
}
}
if( i>=NSORT-1 ){
apSorter[NSORT-1] = page_merge(apSorter[NSORT-1],pPg);
}
}
pToWrite = 0;
for(i=0; i<NSORT; i++){
pToWrite = page_merge(apSorter[i], pToWrite);
}
/* Write all dirty pages back to the database and mark
** them all clean.
*/
lastPgno = 0;
for(pPg=pToWrite; pPg; pPg=pPg->pSort){
if( lastPgno==0 || pPg->pgno!=lastPgno-1 ){
sqliteOsSeek(&pPager->fd, (pPg->pgno-1)*SQLITE_PAGE_SIZE);
}
rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
if( rc!=SQLITE_OK ) break;
pPg->dirty = 0;
lastPgno = pPg->pgno;
}
return rc;
}
@@ -984,10 +1119,11 @@ int sqlitepager_get(Pager *pPager, Pgno pgno, void **ppPage){
}else{
pPg->inJournal = 0;
}
if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize ){
pPg->inCkpt = (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0;
if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize
&& (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0 ){
page_add_to_ckpt_list(pPg);
}else{
pPg->inCkpt = 0;
page_remove_from_ckpt_list(pPg);
}
pPg->dirty = 0;
pPg->nRef = 1;
@@ -1248,7 +1384,7 @@ int sqlitepager_write(void *pData){
pPg->inJournal = 1;
if( pPager->ckptInUse ){
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
page_add_to_ckpt_list(pPg);
}
}
@@ -1268,7 +1404,7 @@ int sqlitepager_write(void *pData){
}
assert( pPager->aInCkpt!=0 );
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
page_add_to_ckpt_list(pPg);
}
/* Update the database size and return.
@@ -1352,14 +1488,14 @@ void sqlitepager_dont_rollback(void *pData){
pPg->inJournal = 1;
if( pPager->ckptInUse ){
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
page_add_to_ckpt_list(pPg);
}
}
if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
assert( pPager->aInCkpt!=0 );
pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
pPg->inCkpt = 1;
page_add_to_ckpt_list(pPg);
}
}
@@ -1521,15 +1657,19 @@ ckpt_begin_failed:
*/
int sqlitepager_ckpt_commit(Pager *pPager){
if( pPager->ckptInUse ){
PgHdr *pPg;
PgHdr *pPg, *pNext;
sqliteOsSeek(&pPager->cpfd, 0);
sqliteOsTruncate(&pPager->cpfd, 0);
pPager->ckptInUse = 0;
sqliteFree( pPager->aInCkpt );
pPager->aInCkpt = 0;
for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
for(pPg=pPager->pCkpt; pPg; pPg=pNext){
pNext = pPg->pNextCkpt;
assert( pPg->inCkpt );
pPg->inCkpt = 0;
pPg->pPrevCkpt = pPg->pNextCkpt = 0;
}
pPager->pCkpt = 0;
}
return SQLITE_OK;
}