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Overview
Comment:Optimization to the sqlite3PcacheFetch() logic.
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SHA1: d9a0481ce0fd9824b1566f182d68ec46ef091b1b
User & Date: drh 2015-06-30 03:57:59
Context
2015-06-30
11:07
Change an unreachable branch into an assert() in sqlite3PagerAcquire() and optimize sqlite3PcacheOpenSavepoint() by factoring out rarely used code into a subroutine. check-in: b406b20e user: drh tags: trunk
03:57
Optimization to the sqlite3PcacheFetch() logic. check-in: d9a0481c user: drh tags: trunk
03:34
Put all variable declarations for sqlite3PagerWrite() at the beginning of the block. Syntax only - no logic changes. check-in: a0fa6b3b user: drh tags: trunk
Changes
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Changes to src/pager.c.

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    {
      sqlite3_pcache_page *pBase;
      pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
      if( pBase==0 ){
        rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);
        if( rc!=SQLITE_OK ) goto pager_acquire_err;





      }
      pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);
      if( pPg==0 ) rc = SQLITE_NOMEM;
    }
  }

  if( rc!=SQLITE_OK ){
................................................................................
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
  sqlite3_pcache_page *pPage;
  assert( pPager!=0 );
  assert( pgno!=0 );
  assert( pPager->pPCache!=0 );
  pPage = sqlite3PcacheFetch(pPager->pPCache, pgno, 0);
  assert( pPage==0 || pPager->hasBeenUsed );

  return sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pPage);
}

/*
** Release a page reference.
**
** If the number of references to the page drop to zero, then the







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    {
      sqlite3_pcache_page *pBase;
      pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
      if( pBase==0 ){
        rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);
        if( rc!=SQLITE_OK ) goto pager_acquire_err;
        if( pBase==0 ){
          pPg = *ppPage = 0;
          rc = SQLITE_NOMEM;
          goto pager_acquire_err;
        }
      }
      pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);
      if( pPg==0 ) rc = SQLITE_NOMEM;
    }
  }

  if( rc!=SQLITE_OK ){
................................................................................
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
  sqlite3_pcache_page *pPage;
  assert( pPager!=0 );
  assert( pgno!=0 );
  assert( pPager->pPCache!=0 );
  pPage = sqlite3PcacheFetch(pPager->pPCache, pgno, 0);
  assert( pPage==0 || pPager->hasBeenUsed );
  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

Changes to src/pcache.c.

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  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;
  assert( pPage!=0 );
  pPgHdr = (PgHdr*)pPage->pExtra;
  assert( pPgHdr->pPage==0 );
 memset(pPgHdr, 0, sizeof(PgHdr));
  pPgHdr->pPage = pPage;
  pPgHdr->pData = pPage->pBuf;
  pPgHdr->pExtra = (void *)&pPgHdr[1];
  memset(pPgHdr->pExtra, 0, pCache->szExtra);
  pPgHdr->pCache = pCache;
  pPgHdr->pgno = pgno;
  pPgHdr->flags = PGHDR_CLEAN;
................................................................................
PgHdr *sqlite3PcacheFetchFinish(
  PCache *pCache,             /* Obtain the page from this cache */
  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;

  if( pPage==0 ) return 0;
  pPgHdr = (PgHdr *)pPage->pExtra;

  if( !pPgHdr->pPage ){
    return pcacheFetchFinishWithInit(pCache, pgno, pPage);
  }
  if( 0==pPgHdr->nRef ){
    pCache->nRef++;







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  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;
  assert( pPage!=0 );
  pPgHdr = (PgHdr*)pPage->pExtra;
  assert( pPgHdr->pPage==0 );
  memset(pPgHdr, 0, sizeof(PgHdr));
  pPgHdr->pPage = pPage;
  pPgHdr->pData = pPage->pBuf;
  pPgHdr->pExtra = (void *)&pPgHdr[1];
  memset(pPgHdr->pExtra, 0, pCache->szExtra);
  pPgHdr->pCache = pCache;
  pPgHdr->pgno = pgno;
  pPgHdr->flags = PGHDR_CLEAN;
................................................................................
PgHdr *sqlite3PcacheFetchFinish(
  PCache *pCache,             /* Obtain the page from this cache */
  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;

  assert( pPage!=0 );
  pPgHdr = (PgHdr *)pPage->pExtra;

  if( !pPgHdr->pPage ){
    return pcacheFetchFinishWithInit(pCache, pgno, pPage);
  }
  if( 0==pPgHdr->nRef ){
    pCache->nRef++;