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Overview
Comment:In the pager, avoid checking for the illegal page number 0 except when creating a new page.
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SHA1: dee20ba982125ea98c280ad1571789af0f393903
User & Date: drh 2016-12-13 18:34:01.957
Context
2016-12-13
18:47
Convert sqlite3PagerGet() into a pointer-dispatched virtual method. This makes it about 25% faster. (check-in: 7f88bb4412 user: drh tags: trunk)
18:34
In the pager, avoid checking for the illegal page number 0 except when creating a new page. (Closed-Leaf check-in: dee20ba982 user: drh tags: pager-get-method)
15:53
Further refinements to the virtual method implementation of sqlite3PagerGet(). (check-in: 67df444648 user: drh tags: pager-get-method)
Changes
Side-by-Side Diff Ignore Whitespace Patch
Changes to src/pager.c.
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  int flags           /* PAGER_GET_XXX flags */
){
  int rc = SQLITE_OK;
  PgHdr *pPg;
  u8 noContent;                   /* True if PAGER_GET_NOCONTENT is set */
  sqlite3_pcache_page *pBase;

  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  assert( pPager->errCode==SQLITE_OK );
  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 ){
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    ** the page. Return without further ado.  */
    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
    pPager->aStat[PAGER_STAT_HIT]++;
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.  */

    ** be initialized. But first some error checks:
    **
    pPg->pPager = pPager;

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
    ** (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 );
    noContent = (flags & PAGER_GET_NOCONTENT)!=0;
    if( !isOpen(pPager->fd) || pPager->dbSize<pgno || noContent ){
      if( pgno>pPager->mxPgno ){
        rc = SQLITE_FULL;
        goto pager_acquire_err;
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Changes to src/pcache.c.
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**
**          assert( sqlite3PcachePageSanity(pPg) );
*/
#if SQLITE_DEBUG
int sqlite3PcachePageSanity(PgHdr *pPg){
  PCache *pCache;
  assert( pPg!=0 );
  assert( pPg->pgno>0 );    /* Page number is 1 or more */
  assert( pPg->pgno>0 || pPg->pPager==0 );    /* Page number is 1 or more */
  pCache = pPg->pCache;
  assert( pCache!=0 );      /* Every page has an associated PCache */
  if( pPg->flags & PGHDR_CLEAN ){
    assert( (pPg->flags & PGHDR_DIRTY)==0 );/* Cannot be both CLEAN and DIRTY */
    assert( pCache->pDirty!=pPg );          /* CLEAN pages not on dirty list */
    assert( pCache->pDirtyTail!=pPg );
  }
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){
  int eCreate;
  sqlite3_pcache_page *pRes;

  assert( pCache!=0 );
  assert( pCache->pCache!=0 );
  assert( createFlag==3 || createFlag==0 );
  assert( pgno>0 );
  assert( pCache->eCreate==((pCache->bPurgeable && pCache->pDirty) ? 1 : 2) );

  /* eCreate defines what to do if the page does not exist.
  **    0     Do not allocate a new page.  (createFlag==0)
  **    1     Allocate a new page if doing so is inexpensive.
  **          (createFlag==1 AND bPurgeable AND pDirty)
  **    2     Allocate a new page even it doing so is difficult.
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