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Write database pages in sorted order to reduce file fragmentation.

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This is an experimental change.  It is not clear if it will help any.
It may well be removed in the future. (CVS 3255)

FossilOrigin-Name: fe3e70a7275d68acb6fb8ea5d62bed3e9d8d2766
This commit is contained in:
drh
2006-06-15 14:31:06 +00:00
parent bdd88bd9f8
commit dc3e10b9c9
3 changed files with 72 additions and 9 deletions
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67
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 1.268 2006/05/07 17:49:39 drh Exp $
** @(#) $Id: pager.c,v 1.269 2006/06/15 14:31:07 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
@@ -161,7 +161,7 @@ struct PgHdr {
u8 needSync; /* Sync journal before writing this page */
u8 alwaysRollback; /* Disable dont_rollback() for this page */
short int nRef; /* Number of users of this page */
PgHdr *pDirty, *pPrevDirty; /* Dirty pages sorted by PgHdr.pgno */
PgHdr *pDirty, *pPrevDirty; /* Dirty pages */
u32 notUsed; /* Buffer space */
#ifdef SQLITE_CHECK_PAGES
u32 pageHash;
@@ -2260,6 +2260,68 @@ static int syncJournal(Pager *pPager){
return rc;
}
/*
** Merge two lists of pages connected by pDirty and in pgno order.
** Do not both fixing the pPrevDirty pointers.
*/
static PgHdr *merge_pagelist(PgHdr *pA, PgHdr *pB){
PgHdr result, *pTail;
pTail = &result;
while( pA && pB ){
if( pA->pgno<pB->pgno ){
pTail->pDirty = pA;
pTail = pA;
pA = pA->pDirty;
}else{
pTail->pDirty = pB;
pTail = pB;
pB = pB->pDirty;
}
}
if( pA ){
pTail->pDirty = pA;
}else if( pB ){
pTail->pDirty = pB;
}else{
pTail->pDirty = 0;
}
return result.pDirty;
}
/*
** Sort the list of pages in accending order by pgno. Pages are
** connected by pDirty pointers. The pPrevDirty pointers are
** corrupted by this sort.
*/
#define N_SORT_BUCKET 25
static PgHdr *sort_pagelist(PgHdr *pIn){
PgHdr *a[N_SORT_BUCKET], *p;
int i;
memset(a, 0, sizeof(a));
while( pIn ){
p = pIn;
pIn = p->pDirty;
p->pDirty = 0;
for(i=0; i<N_SORT_BUCKET-1; i++){
if( a[i]==0 ){
a[i] = p;
break;
}else{
p = merge_pagelist(a[i], p);
a[i] = 0;
}
}
if( i==N_SORT_BUCKET-1 ){
a[i] = merge_pagelist(a[i], p);
}
}
p = a[0];
for(i=1; i<N_SORT_BUCKET; i++){
p = merge_pagelist(p, a[i]);
}
return p;
}
/*
** Given a list of pages (connected by the PgHdr.pDirty pointer) write
** every one of those pages out to the database file and mark them all
@@ -2293,6 +2355,7 @@ static int pager_write_pagelist(PgHdr *pList){
return rc;
}
pList = sort_pagelist(pList);
while( pList ){
assert( pList->dirty );
rc = sqlite3OsSeek(pPager->fd, (pList->pgno-1)*(i64)pPager->pageSize);