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Overview
Comment:Add the new sqlite3PagerUnrefPageOne() pager method to deal with the special case of unreferencing page1.
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SHA3-256:b2e2100cf766da1cb499aec0ca0a9969d7af5d93312ab8cf895fbf4a6ffb9b2f
User & Date: drh 2017-09-01 14:50:19
Context
2017-09-04
00:19
Fix recent test cases in test/indexepxr2.test so that they work even without SQLITE_ENABLE_STAT4 and SQLITE_ENABLE_JSON1. check-in: 03f3cc03 user: drh tags: trunk
2017-09-01
14:50
Add the new sqlite3PagerUnrefPageOne() pager method to deal with the special case of unreferencing page1. check-in: b2e2100c user: drh tags: trunk
12:57
Remove an obsolete optimization in pcache that due to more recent changes was recently making the code a little slower. check-in: c4e7e175 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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      pLock->eLock = READ_LOCK;
    }
  }
}

#endif /* SQLITE_OMIT_SHARED_CACHE */

static void releasePage(MemPage *pPage);

static void releasePageNotNull(MemPage *pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
*/
................................................................................
  assert( pgno!=0 || rc==SQLITE_CORRUPT );
  return rc;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to btreeGetPage.


*/
static void releasePageNotNull(MemPage *pPage){
  assert( pPage->aData );
  assert( pPage->pBt );
  assert( pPage->pDbPage!=0 );
  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
  assert( sqlite3PagerGetData(pPage->pDbPage)==pPage->aData );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  sqlite3PagerUnrefNotNull(pPage->pDbPage);
}
static void releasePage(MemPage *pPage){
  if( pPage ) releasePageNotNull(pPage);










}

/*
** Get an unused page.
**
** This works just like btreeGetPage() with the addition:
**
................................................................................
      int isOpen = 0;
      rc = sqlite3PagerOpenWal(pBt->pPager, &isOpen);
      if( rc!=SQLITE_OK ){
        goto page1_init_failed;
      }else{
        setDefaultSyncFlag(pBt, SQLITE_DEFAULT_WAL_SYNCHRONOUS+1);
        if( isOpen==0 ){
          releasePage(pPage1);
          return SQLITE_OK;
        }
      }
      rc = SQLITE_NOTADB;
    }else{
      setDefaultSyncFlag(pBt, SQLITE_DEFAULT_SYNCHRONOUS+1);
    }
................................................................................
    if( (u32)pageSize!=pBt->pageSize ){
      /* After reading the first page of the database assuming a page size
      ** of BtShared.pageSize, we have discovered that the page-size is
      ** actually pageSize. Unlock the database, leave pBt->pPage1 at
      ** zero and return SQLITE_OK. The caller will call this function
      ** again with the correct page-size.
      */
      releasePage(pPage1);
      pBt->usableSize = usableSize;
      pBt->pageSize = pageSize;
      freeTempSpace(pBt);
      rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize,
                                   pageSize-usableSize);
      return rc;
    }
................................................................................
  }
  assert( pBt->maxLeaf + 23 <= MX_CELL_SIZE(pBt) );
  pBt->pPage1 = pPage1;
  pBt->nPage = nPage;
  return SQLITE_OK;

page1_init_failed:
  releasePage(pPage1);
  pBt->pPage1 = 0;
  return rc;
}

#ifndef NDEBUG
/*
** Return the number of cursors open on pBt. This is for use
................................................................................
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( countValidCursors(pBt,0)==0 || pBt->inTransaction>TRANS_NONE );
  if( pBt->inTransaction==TRANS_NONE && pBt->pPage1!=0 ){
    MemPage *pPage1 = pBt->pPage1;
    assert( pPage1->aData );
    assert( sqlite3PagerRefcount(pBt->pPager)==1 );
    pBt->pPage1 = 0;
    releasePageNotNull(pPage1);
  }
}

/*
** If pBt points to an empty file then convert that empty file
** into a new empty database by initializing the first page of
** the database.
................................................................................
    ** sure pPage1->aData is set correctly. */
    if( btreeGetPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
      int nPage = get4byte(28+(u8*)pPage1->aData);
      testcase( nPage==0 );
      if( nPage==0 ) sqlite3PagerPagecount(pBt->pPager, &nPage);
      testcase( pBt->nPage!=nPage );
      pBt->nPage = nPage;
      releasePage(pPage1);
    }
    assert( countValidCursors(pBt, 1)==0 );
    pBt->inTransaction = TRANS_READ;
    btreeClearHasContent(pBt);
  }

  btreeEndTransaction(p);







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      pLock->eLock = READ_LOCK;
    }
  }
}

#endif /* SQLITE_OMIT_SHARED_CACHE */

static void releasePage(MemPage *pPage);         /* Forward reference */
static void releasePageOne(MemPage *pPage);      /* Forward reference */
static void releasePageNotNull(MemPage *pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
*/
................................................................................
  assert( pgno!=0 || rc==SQLITE_CORRUPT );
  return rc;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to btreeGetPage.
**
** Page1 is a special case and must be released using releasePageOne().
*/
static void releasePageNotNull(MemPage *pPage){
  assert( pPage->aData );
  assert( pPage->pBt );
  assert( pPage->pDbPage!=0 );
  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
  assert( sqlite3PagerGetData(pPage->pDbPage)==pPage->aData );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  sqlite3PagerUnrefNotNull(pPage->pDbPage);
}
static void releasePage(MemPage *pPage){
  if( pPage ) releasePageNotNull(pPage);
}
static void releasePageOne(MemPage *pPage){
  assert( pPage!=0 );
  assert( pPage->aData );
  assert( pPage->pBt );
  assert( pPage->pDbPage!=0 );
  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
  assert( sqlite3PagerGetData(pPage->pDbPage)==pPage->aData );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  sqlite3PagerUnrefPageOne(pPage->pDbPage);
}

/*
** Get an unused page.
**
** This works just like btreeGetPage() with the addition:
**
................................................................................
      int isOpen = 0;
      rc = sqlite3PagerOpenWal(pBt->pPager, &isOpen);
      if( rc!=SQLITE_OK ){
        goto page1_init_failed;
      }else{
        setDefaultSyncFlag(pBt, SQLITE_DEFAULT_WAL_SYNCHRONOUS+1);
        if( isOpen==0 ){
          releasePageOne(pPage1);
          return SQLITE_OK;
        }
      }
      rc = SQLITE_NOTADB;
    }else{
      setDefaultSyncFlag(pBt, SQLITE_DEFAULT_SYNCHRONOUS+1);
    }
................................................................................
    if( (u32)pageSize!=pBt->pageSize ){
      /* After reading the first page of the database assuming a page size
      ** of BtShared.pageSize, we have discovered that the page-size is
      ** actually pageSize. Unlock the database, leave pBt->pPage1 at
      ** zero and return SQLITE_OK. The caller will call this function
      ** again with the correct page-size.
      */
      releasePageOne(pPage1);
      pBt->usableSize = usableSize;
      pBt->pageSize = pageSize;
      freeTempSpace(pBt);
      rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize,
                                   pageSize-usableSize);
      return rc;
    }
................................................................................
  }
  assert( pBt->maxLeaf + 23 <= MX_CELL_SIZE(pBt) );
  pBt->pPage1 = pPage1;
  pBt->nPage = nPage;
  return SQLITE_OK;

page1_init_failed:
  releasePageOne(pPage1);
  pBt->pPage1 = 0;
  return rc;
}

#ifndef NDEBUG
/*
** Return the number of cursors open on pBt. This is for use
................................................................................
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( countValidCursors(pBt,0)==0 || pBt->inTransaction>TRANS_NONE );
  if( pBt->inTransaction==TRANS_NONE && pBt->pPage1!=0 ){
    MemPage *pPage1 = pBt->pPage1;
    assert( pPage1->aData );
    assert( sqlite3PagerRefcount(pBt->pPager)==1 );
    pBt->pPage1 = 0;
    releasePageOne(pPage1);
  }
}

/*
** If pBt points to an empty file then convert that empty file
** into a new empty database by initializing the first page of
** the database.
................................................................................
    ** sure pPage1->aData is set correctly. */
    if( btreeGetPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
      int nPage = get4byte(28+(u8*)pPage1->aData);
      testcase( nPage==0 );
      if( nPage==0 ) sqlite3PagerPagecount(pBt->pPager, &nPage);
      testcase( pBt->nPage!=nPage );
      pBt->nPage = nPage;
      releasePageOne(pPage1);
    }
    assert( countValidCursors(pBt, 1)==0 );
    pBt->inTransaction = TRANS_READ;
    btreeClearHasContent(pBt);
  }

  btreeEndTransaction(p);

Changes to src/pager.c.

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** transaction and unlock the pager.
**
** Except, in locking_mode=EXCLUSIVE when there is nothing to in
** the rollback journal, the unlock is not performed and there is
** nothing to rollback, so this routine is a no-op.
*/ 
static void pagerUnlockIfUnused(Pager *pPager){
  if( pPager->nMmapOut==0 && (sqlite3PcacheRefCount(pPager->pPCache)==0) ){

    pagerUnlockAndRollback(pPager);
  }
}

/*
** The page getter methods each try to acquire a reference to a
** page with page number pgno. If the requested reference is 
................................................................................
  if( pPage==0 ) return 0;
  return sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pPage);
}

/*
** 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.




*/
void sqlite3PagerUnrefNotNull(DbPage *pPg){
  Pager *pPager;
  assert( pPg!=0 );
  pPager = pPg->pPager;
  if( pPg->flags & PGHDR_MMAP ){

    pagerReleaseMapPage(pPg);
  }else{
    sqlite3PcacheRelease(pPg);
  }
  pagerUnlockIfUnused(pPager);

}
void sqlite3PagerUnref(DbPage *pPg){
  if( pPg ) sqlite3PagerUnrefNotNull(pPg);









}

/*
** This function is called at the start of every write transaction.
** There must already be a RESERVED or EXCLUSIVE lock on the database 
** file when this routine is called.
**







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** transaction and unlock the pager.
**
** Except, in locking_mode=EXCLUSIVE when there is nothing to in
** the rollback journal, the unlock is not performed and there is
** nothing to rollback, so this routine is a no-op.
*/ 
static void pagerUnlockIfUnused(Pager *pPager){
  if( sqlite3PcacheRefCount(pPager->pPCache)==0 ){
    assert( pPager->nMmapOut==0 ); /* because page1 is never memory mapped */
    pagerUnlockAndRollback(pPager);
  }
}

/*
** The page getter methods each try to acquire a reference to a
** page with page number pgno. If the requested reference is 
................................................................................
  if( pPage==0 ) return 0;
  return sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pPage);
}

/*
** Release a page reference.
**
** 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){
  TESTONLY( Pager *pPager = pPg->pPager; )
  assert( pPg!=0 );

  if( pPg->flags & PGHDR_MMAP ){
    assert( pPg->pgno!=1 );  /* Page1 is never memory mapped */
    pagerReleaseMapPage(pPg);
  }else{
    sqlite3PcacheRelease(pPg);
  }
  /* 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.
** There must already be a RESERVED or EXCLUSIVE lock on the database 
** file when this routine is called.
**

Changes to src/pager.h.

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/* Functions used to obtain and release page references. */ 
int sqlite3PagerGet(Pager *pPager, Pgno pgno, DbPage **ppPage, int clrFlag);
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno);
void sqlite3PagerRef(DbPage*);
void sqlite3PagerUnref(DbPage*);
void sqlite3PagerUnrefNotNull(DbPage*);


/* Operations on page references. */
int sqlite3PagerWrite(DbPage*);
void sqlite3PagerDontWrite(DbPage*);
int sqlite3PagerMovepage(Pager*,DbPage*,Pgno,int);
int sqlite3PagerPageRefcount(DbPage*);
void *sqlite3PagerGetData(DbPage *); 







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/* Functions used to obtain and release page references. */ 
int sqlite3PagerGet(Pager *pPager, Pgno pgno, DbPage **ppPage, int clrFlag);
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno);
void sqlite3PagerRef(DbPage*);
void sqlite3PagerUnref(DbPage*);
void sqlite3PagerUnrefNotNull(DbPage*);
void sqlite3PagerUnrefPageOne(DbPage*);

/* Operations on page references. */
int sqlite3PagerWrite(DbPage*);
void sqlite3PagerDontWrite(DbPage*);
int sqlite3PagerMovepage(Pager*,DbPage*,Pgno,int);
int sqlite3PagerPageRefcount(DbPage*);
void *sqlite3PagerGetData(DbPage *);