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Overview
Comment:Add the new PGHDR_CLEAN bit to PgHdr.flags in pcache.c. This bit is always the opposite of PGHDR_DIRTY. Use the extra bit to avoid a comparison for a small performance boost.
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SHA1:8619fc346d9a5a66a3c4566b4cc032b6b6bf73fd
User & Date: drh 2015-06-29 04:21:15
Context
2015-06-29
14:11
Simplifications and performance improvement in pager_write(). check-in: ab7aeeea user: drh tags: trunk
04:21
Add the new PGHDR_CLEAN bit to PgHdr.flags in pcache.c. This bit is always the opposite of PGHDR_DIRTY. Use the extra bit to avoid a comparison for a small performance boost. check-in: 8619fc34 user: drh tags: trunk
03:28
Very small size reduction and performance increase in sqlite3BitvecTest(). check-in: 9b3a7281 user: drh tags: trunk
Changes
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Changes to src/pcache.c.

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 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;

  return sqlite3PcacheFetchFinish(pCache,pgno,pPage);
}

/*
** This routine converts the sqlite3_pcache_page object returned by
** sqlite3PcacheFetch() into an initialized PgHdr object.  This routine
** must be called after sqlite3PcacheFetch() in order to get a usable
................................................................................
** reference count drops to 0, then it is made eligible for recycling.
*/
void SQLITE_NOINLINE sqlite3PcacheRelease(PgHdr *p){
  assert( p->nRef>0 );
  p->nRef--;
  if( p->nRef==0 ){
    p->pCache->nRef--;
    if( (p->flags&PGHDR_DIRTY)==0 ){
      pcacheUnpin(p);
    }else if( p->pDirtyPrev!=0 ){
      /* Move the page to the head of the dirty list. */
      pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
    }
  }
}
................................................................................
}

/*
** Make sure the page is marked as dirty. If it isn't dirty already,
** make it so.
*/
void sqlite3PcacheMakeDirty(PgHdr *p){
  p->flags &= ~PGHDR_DONT_WRITE;
  assert( p->nRef>0 );

  if( 0==(p->flags & PGHDR_DIRTY) ){
    p->flags |= PGHDR_DIRTY;


    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_ADD);

  }
}

/*
** Make sure the page is marked as clean. If it isn't clean already,
** make it so.
*/
void sqlite3PcacheMakeClean(PgHdr *p){
  if( (p->flags & PGHDR_DIRTY) ){

    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
    p->flags &= ~(PGHDR_DIRTY|PGHDR_NEED_SYNC);

    if( p->nRef==0 ){
      pcacheUnpin(p);
    }
  }
}

/*







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 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;
  return sqlite3PcacheFetchFinish(pCache,pgno,pPage);
}

/*
** This routine converts the sqlite3_pcache_page object returned by
** sqlite3PcacheFetch() into an initialized PgHdr object.  This routine
** must be called after sqlite3PcacheFetch() in order to get a usable
................................................................................
** reference count drops to 0, then it is made eligible for recycling.
*/
void SQLITE_NOINLINE sqlite3PcacheRelease(PgHdr *p){
  assert( p->nRef>0 );
  p->nRef--;
  if( p->nRef==0 ){
    p->pCache->nRef--;
    if( p->flags&PGHDR_CLEAN ){
      pcacheUnpin(p);
    }else if( p->pDirtyPrev!=0 ){
      /* Move the page to the head of the dirty list. */
      pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
    }
  }
}
................................................................................
}

/*
** Make sure the page is marked as dirty. If it isn't dirty already,
** make it so.
*/
void sqlite3PcacheMakeDirty(PgHdr *p){

  assert( p->nRef>0 );
  if( p->flags & (PGHDR_CLEAN|PGHDR_DONT_WRITE) ){
    p->flags &= ~PGHDR_DONT_WRITE;
    if( p->flags & PGHDR_CLEAN ){
      p->flags ^= (PGHDR_DIRTY|PGHDR_CLEAN);
      assert( (p->flags & (PGHDR_DIRTY|PGHDR_CLEAN))==PGHDR_DIRTY );
      pcacheManageDirtyList(p, PCACHE_DIRTYLIST_ADD);
    }
  }
}

/*
** Make sure the page is marked as clean. If it isn't clean already,
** make it so.
*/
void sqlite3PcacheMakeClean(PgHdr *p){
  if( (p->flags & PGHDR_DIRTY) ){
    assert( (p->flags & PGHDR_CLEAN)==0 );
    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
    p->flags &= ~(PGHDR_DIRTY|PGHDR_NEED_SYNC);
    p->flags |= PGHDR_CLEAN;
    if( p->nRef==0 ){
      pcacheUnpin(p);
    }
  }
}

/*

Changes to src/pcache.h.

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  PCache *pCache;                /* Cache that owns this page */

  PgHdr *pDirtyNext;             /* Next element in list of dirty pages */
  PgHdr *pDirtyPrev;             /* Previous element in list of dirty pages */
};

/* Bit values for PgHdr.flags */

#define PGHDR_DIRTY             0x002  /* Page has changed */
#define PGHDR_NEED_SYNC         0x004  /* Fsync the rollback journal before
                                       ** writing this page to the database */
#define PGHDR_NEED_READ         0x008  /* Content is unread */
#define PGHDR_REUSE_UNLIKELY    0x010  /* A hint that reuse is unlikely */
#define PGHDR_DONT_WRITE        0x020  /* Do not write content to disk */








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  PCache *pCache;                /* Cache that owns this page */

  PgHdr *pDirtyNext;             /* Next element in list of dirty pages */
  PgHdr *pDirtyPrev;             /* Previous element in list of dirty pages */
};

/* Bit values for PgHdr.flags */
#define PGHDR_CLEAN             0x001  /* Page is unchanged */
#define PGHDR_DIRTY             0x002  /* Page has changed */
#define PGHDR_NEED_SYNC         0x004  /* Fsync the rollback journal before
                                       ** writing this page to the database */
#define PGHDR_NEED_READ         0x008  /* Content is unread */
#define PGHDR_REUSE_UNLIKELY    0x010  /* A hint that reuse is unlikely */
#define PGHDR_DONT_WRITE        0x020  /* Do not write content to disk */