SQLite: Changes On Branch pcache1-zero-page

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Changes In Branch pcache1-zero-page Excluding Merge-Ins

This is equivalent to a diff from 2842bc60 to b0810ac1

2016-12-30
14:15		Avoid passing NULL pointers to memcmp() or memcpy(), even when the "number-of-bytes" argument is passed 0. (check-in: 56ff72ab user: dan tags: trunk)
13:55		Clarify the expectations for the behavior of the xFetch method on the sqlite3_pcache_methods object for the case when the key is zero. (Closed-Leaf check-in: b0810ac1 user: drh tags: pcache1-zero-page)
13:40		Improved detection of zero page numbers in the page cache. (check-in: 5550e815 user: drh tags: pcache1-zero-page)
12:10		Fix a harmless compiler warning in fuzzcheck.c (check-in: 2842bc60 user: drh tags: trunk)
12:06		Disable the pagerAcquireMapPage() routine if memory-mapped I/O is disabled. This fixes a harmless compiler warning on OpenBSD. (check-in: 3e25ba6e user: drh tags: trunk)

Changes to src/pager.c.

  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );
  assert( pPager->hasHeldSharedLock==1 );

  pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
  if( pBase==0 ){
    pPg = 0;



    rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);

    if( rc!=SQLITE_OK ) goto pager_acquire_err;
    if( pBase==0 ){
      rc = SQLITE_NOMEM_BKPT;
      goto pager_acquire_err;
    }
  }
  pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);
................................................................................
    pPager->aStat[PAGER_STAT_HIT]++;
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized. But first some error checks:
    **
    ** (1) Minimum page number is 1
    ** (2) The maximum page number is 2^31
    ** (3) Never try to fetch the locking page
    */

    if( pgno==0 || pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }

    pPg->pPager = pPager;

    assert( !isOpen(pPager->fd) || !MEMDB );








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  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );
  assert( pPager->hasHeldSharedLock==1 );

  pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
  if( pBase==0 ){
    pPg = 0;
    if( pgno==0 ){
      rc = SQLITE_CORRUPT_BKPT;
    }else{
      rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);
    }
    if( rc!=SQLITE_OK ) goto pager_acquire_err;
    if( pBase==0 ){
      rc = SQLITE_NOMEM_BKPT;
      goto pager_acquire_err;
    }
  }
  pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);
................................................................................
    pPager->aStat[PAGER_STAT_HIT]++;
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized. But first some error checks:
    **

    ** (1) The maximum page number is 2^31
    ** (2) Never try to fetch the locking page
    */
    assert( pgno>0 );
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }

    pPg->pPager = pPager;

    assert( !isOpen(pPager->fd) || !MEMDB );

Changes to src/pcache1.c.

  ** subsequent steps to try to create the page. */
  if( pPage ){
    if( !pPage->isPinned ){
      return pcache1PinPage(pPage);
    }else{
      return pPage;
    }
  }else if( createFlag ){
    /* Steps 3, 4, and 5 implemented by this subroutine */
    return pcache1FetchStage2(pCache, iKey, createFlag);
  }else{
    return 0;
  }
}
#if PCACHE1_MIGHT_USE_GROUP_MUTEX

  ** subsequent steps to try to create the page. */
  if( pPage ){
    if( !pPage->isPinned ){
      return pcache1PinPage(pPage);
    }else{
      return pPage;
    }
  }else if( createFlag && iKey ){
    /* Steps 3, 4, and 5 implemented by this subroutine */
    return pcache1FetchStage2(pCache, iKey, createFlag);
  }else{
    return 0;
  }
}
#if PCACHE1_MIGHT_USE_GROUP_MUTEX

Changes to src/sqlite.h.in.

** The pBuf element of the returned sqlite3_pcache_page object will be a
** pointer to a buffer of szPage bytes used to store the content of a 
** single database page.  The pExtra element of sqlite3_pcache_page will be
** a pointer to the szExtra bytes of extra storage that SQLite has requested
** for each entry in the page cache.
**
** The page to be fetched is determined by the key. ^The minimum key value

** is 1.  After it has been retrieved using xFetch, the page is considered
** to be "pinned".
**
** If the requested page is already in the page cache, then the page cache
** implementation must return a pointer to the page buffer with its content
** intact.  If the requested page is not already in the cache, then the
** cache implementation should use the value of the createFlag
** parameter to help it determined what action to take:
**
** <table border=1 width=85% align=center>
** <tr><th> createFlag <th> Behavior when page is not already in cache
** <tr><td> 0 <td> Do not allocate a new page.  Return NULL.
** <tr><td> 1 <td> Allocate a new page if it easy and convenient to do so.
**                 Otherwise return NULL.
** <tr><td> 2 <td> Make every effort to allocate a new page.  Only return

**                 NULL if allocating a new page is effectively impossible.
** </table>
**
** ^(SQLite will normally invoke xFetch() with a createFlag of 0 or 1.  SQLite
** will only use a createFlag of 2 after a prior call with a createFlag of 1
** failed.)^  In between the to xFetch() calls, SQLite may
** attempt to unpin one or more cache pages by spilling the content of
** pinned pages to disk and synching the operating system disk cache.








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** The pBuf element of the returned sqlite3_pcache_page object will be a
** pointer to a buffer of szPage bytes used to store the content of a 
** single database page.  The pExtra element of sqlite3_pcache_page will be
** a pointer to the szExtra bytes of extra storage that SQLite has requested
** for each entry in the page cache.
**
** The page to be fetched is determined by the key. ^The minimum key value
** is 1.  The xFetch() method must return NULL if passed a key of 0.
** After it has been retrieved using xFetch, the page is considered
** to be "pinned".
**
** If the requested page is already in the page cache, then the page cache
** implementation must return a pointer to the page buffer with its content
** intact.  If the requested page is not already in the cache, then the
** cache implementation should use the value of the createFlag
** parameter to help it determined what action to take:
**
** <table border=1 width=85% align=center>
** <tr><th> createFlag <th> Behavior when page is not already in cache
** <tr><td> 0 <td> Do not allocate a new page.  Return NULL.
** <tr><td> 1 <td> Allocate a new page if it easy and convenient to do so
**                 and the key is not zero.  Otherwise return NULL.
** <tr><td> 2 <td> Make every effort to allocate a new page.  Only return
**                 NULL if the key is zero or if allocating a new page is 
**                 effectively impossible.
** </table>
**
** ^(SQLite will normally invoke xFetch() with a createFlag of 0 or 1.  SQLite
** will only use a createFlag of 2 after a prior call with a createFlag of 1
** failed.)^  In between the to xFetch() calls, SQLite may
** attempt to unpin one or more cache pages by spilling the content of
** pinned pages to disk and synching the operating system disk cache.