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Add the new sqlite3PagerUnrefPageOne() pager method to deal with the special

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case of unreferencing page1.

FossilOrigin-Name: b2e2100cf766da1cb499aec0ca0a9969d7af5d93312ab8cf895fbf4a6ffb9b2f
This commit is contained in:
drh
2017-09-01 14:50:19 +00:00
parent dfcdc663f2
commit 3908fe90b1
5 changed files with 52 additions and 23 deletions
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31
src/pager.c
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@@ -5350,7 +5350,8 @@ int sqlite3PagerSharedLock(Pager *pPager){
** nothing to rollback, so this routine is a no-op.
*/
static void pagerUnlockIfUnused(Pager *pPager){
if( pPager->nMmapOut==0 && (sqlite3PcacheRefCount(pPager->pPCache)==0) ){
if( sqlite3PcacheRefCount(pPager->pPCache)==0 ){
assert( pPager->nMmapOut==0 ); /* because page1 is never memory mapped */
pagerUnlockAndRollback(pPager);
}
}
@@ -5636,25 +5637,39 @@ DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
/*
** Release a page reference.
**
** If the number of references to the page drop to zero, then the
** page is added to the LRU list. When all references to all pages
** are released, a rollback occurs and the lock on the database is
** removed.
** The sqlite3PagerUnref() and sqlite3PagerUnrefNotNull() may only be
** used if we know that the page being released is not the last page.
** The btree layer always holds page1 open until the end, so these first
** to routines can be used to release any page other than BtShared.pPage1.
**
** Use sqlite3PagerUnrefPageOne() to release page1. This latter routine
** checks the total number of outstanding pages and if the number of
** pages reaches zero it drops the database lock.
*/
void sqlite3PagerUnrefNotNull(DbPage *pPg){
Pager *pPager;
TESTONLY( Pager *pPager = pPg->pPager; )
assert( pPg!=0 );
pPager = pPg->pPager;
if( pPg->flags & PGHDR_MMAP ){
assert( pPg->pgno!=1 ); /* Page1 is never memory mapped */
pagerReleaseMapPage(pPg);
}else{
sqlite3PcacheRelease(pPg);
}
pagerUnlockIfUnused(pPager);
/* Do not use this routine to release the last reference to page1 */
assert( sqlite3PcacheRefCount(pPager->pPCache)>0 );
}
void sqlite3PagerUnref(DbPage *pPg){
if( pPg ) sqlite3PagerUnrefNotNull(pPg);
}
void sqlite3PagerUnrefPageOne(DbPage *pPg){
Pager *pPager;
assert( pPg!=0 );
assert( pPg->pgno==1 );
assert( (pPg->flags & PGHDR_MMAP)==0 ); /* Page1 is never memory mapped */
pPager = pPg->pPager;
sqlite3PcacheRelease(pPg);
pagerUnlockIfUnused(pPager);
}
/*
** This function is called at the start of every write transaction.