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Add some comments and test-cases for the global lru page list (used by sqlite3_release_memory()). (CVS 4308)

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FossilOrigin-Name: 0b80168895993af5774369f839f284712d006f0a
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danielk1977
2007-08-28 08:00:17 +00:00
parent 900b31ef49
commit 84f786fcdd
4 changed files with 194 additions and 22 deletions
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78
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 1.377 2007/08/27 17:27:49 danielk1977 Exp $
** @(#) $Id: pager.c,v 1.378 2007/08/28 08:00:18 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
@@ -132,6 +132,33 @@
#define FORCE_ALIGNMENT(X) (((X)+7)&~7)
typedef struct PgHdr PgHdr;
/*
** Each pager stores all currently unreferenced pages in a list sorted
** in least-recently-used (LRU) order (i.e. the first item on the list has
** not been referenced in a long time, the last item has been recently
** used). An instance of this structure is included as part of each
** pager structure for this purpose (variable Pager.lru).
**
** Additionally, if memory-management is enabled, all unreferenced pages
** are stored in a global LRU list (global variable sqlite3LruPageList).
**
** In both cases, the PagerLruList.pFirstSynced variable points to
** the first page in the corresponding list that does not require an
** fsync() operation before it's memory can be reclaimed. If no such
** page exists, PagerLruList.pFirstSynced is set to NULL.
*/
typedef struct PagerLruList PagerLruList;
struct PagerLruList {
PgHdr *pFirst; /* First page in LRU list */
PgHdr *pLast; /* Last page in LRU list (the most recently used) */
PgHdr *pFirstSynced; /* First page in list with PgHdr.needSync==0 */
};
/*
** The following structure contains the next and previous pointers used
** to link a PgHdr structure into a PagerLruList linked list.
*/
typedef struct PagerLruLink PagerLruLink;
struct PagerLruLink {
PgHdr *pNext;
@@ -292,13 +319,6 @@ struct PgHistory {
#define PGHDR_TO_HIST(P,PGR) \
((PgHistory*)&((char*)(&(P)[1]))[(PGR)->pageSize+(PGR)->nExtra])
typedef struct PagerLruList PagerLruList;
struct PagerLruList {
PgHdr *pFirst;
PgHdr *pLast;
PgHdr *pFirstSynced; /* First page in list with PgHdr.needSync==0 */
};
/*
** A open page cache is an instance of the following structure.
**
@@ -531,10 +551,22 @@ static const unsigned char aJournalMagic[] = {
# define REFINFO(X)
#endif
/*
** Add page pPg to the end of the linked list managed by structure
** pList (pPg becomes the last entry in the list - the most recently
** used). Argument pLink should point to either pPg->free or pPg->gfree,
** depending on whether pPg is being added to the pager-specific or
** global LRU list.
*/
static void listAdd(PagerLruList *pList, PagerLruLink *pLink, PgHdr *pPg){
pLink->pNext = 0;
pLink->pPrev = pList->pLast;
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
assert(pLink==&pPg->free || pLink==&pPg->gfree);
assert(pLink==&pPg->gfree || pList!=&sqlite3LruPageList);
#endif
if( pList->pLast ){
int iOff = (char *)pLink - (char *)pPg;
PagerLruLink *pLastLink = (PagerLruLink *)(&((u8 *)pList->pLast)[iOff]);
@@ -550,9 +582,20 @@ static void listAdd(PagerLruList *pList, PagerLruLink *pLink, PgHdr *pPg){
}
}
/*
** Remove pPg from the list managed by the structure pointed to by pList.
**
** Argument pLink should point to either pPg->free or pPg->gfree, depending
** on whether pPg is being added to the pager-specific or global LRU list.
*/
static void listRemove(PagerLruList *pList, PagerLruLink *pLink, PgHdr *pPg){
int iOff = (char *)pLink - (char *)pPg;
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
assert(pLink==&pPg->free || pLink==&pPg->gfree);
assert(pLink==&pPg->gfree || pList!=&sqlite3LruPageList);
#endif
if( pPg==pList->pFirst ){
pList->pFirst = pLink->pNext;
}
@@ -580,7 +623,9 @@ static void listRemove(PagerLruList *pList, PagerLruLink *pLink, PgHdr *pPg){
}
/*
** Add page to the free-list
** Add page pPg to the list of free pages for the pager. If
** memory-management is enabled, also add the page to the global
** list of free pages.
*/
static void lruListAdd(PgHdr *pPg){
listAdd(&pPg->pPager->lru, &pPg->free, pPg);
@@ -594,7 +639,9 @@ static void lruListAdd(PgHdr *pPg){
}
/*
** Remove page from free-list
** Remove page pPg from the list of free pages for the associated pager.
** If memory-management is enabled, also remove pPg from the global list
** of free pages.
*/
static void lruListRemove(PgHdr *pPg){
listRemove(&pPg->pPager->lru, &pPg->free, pPg);
@@ -608,7 +655,11 @@ static void lruListRemove(PgHdr *pPg){
}
/*
** Set the Pager.pFirstSynced variable
** This function is called just after the needSync flag has been cleared
** from all pages managed by pPager (usually because the journal file
** has just been synced). It updates the pPager->lru.pFirstSynced variable
** and, if memory-management is enabled, the sqlite3LruPageList.pFirstSynced
** variable also.
*/
static void lruListSetFirstSynced(Pager *pPager){
pPager->lru.pFirstSynced = pPager->lru.pFirst;
@@ -3056,6 +3107,10 @@ int sqlite3PagerReleaseMemory(int nReq){
}
sqlite3_mutex_leave(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU));
/* If pPg==0, then the block above has failed to find a page to
** recycle. In this case return early - no further memory will
** be released.
*/
if( !pPg ) break;
pPager = pPg->pPager;
@@ -3089,6 +3144,7 @@ int sqlite3PagerReleaseMemory(int nReq){
IOTRACE(("PGFREE %p %d *\n", pPager, pPg->pgno));
PAGER_INCR(sqlite3_pager_pgfree_count);
sqlite3_free(pPg);
pPager->nPage--;
}else{
/* An error occured whilst writing to the database file or
** journal in pager_recycle(). The error is not returned to the