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Back out the changes in the pager that sorted pages prior to writing them

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to the database.  Additional measurements showed no performance gains. (CVS 785)

FossilOrigin-Name: 745d66395daf5cb8463305bbc9e4219534d2b7cf
This commit is contained in:
drh
2002-11-11 01:04:47 +00:00
parent 32c05e993f
commit 4d9ef4c4ef
3 changed files with 18 additions and 98 deletions
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102
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 1.57 2002/11/10 23:32:57 drh Exp $
** @(#) $Id: pager.c,v 1.58 2002/11/11 01:04:48 drh Exp $
*/
#include "os.h" /* Must be first to enable large file support */
#include "sqliteInt.h"
@@ -75,7 +75,6 @@ struct PgHdr {
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 */
@@ -794,41 +793,6 @@ 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.
@@ -845,19 +809,10 @@ static PgHdr *page_merge(PgHdr *pLeft, PgHdr *pRight){
** 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
@@ -871,56 +826,21 @@ static int syncAllPages(Pager *pPager){
pPager->needSync = 0;
}
/* Create a list of all dirty pages
/* Write all dirty free pages to the disk in the order that they
** appear on the disk. We have experimented with sorting the pages
** by page numbers so that they are written in order, but that does
** not appear to improve performance.
*/
pToWrite = 0;
for(pPg=pPager->pFirst; pPg; pPg=pPg->pNextFree){
if( pPg->dirty ){
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( 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;
}
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;
}