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Overview
Comment:Change the definition of SQLITE_CONFIG_SCRATCH so that at most one scratch buffer is used per thread. Use the generic heap memory allocator for the WalIterator object when running a checkpoint.
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SHA1: 391c9b85abcb5ba300fb2e116384639310c69ed2
User & Date: drh 2014-11-04 14:22:27
Context
2014-11-04
17:23
Add various requirements evidence marks for sqlite3_config() options. check-in: d423349d user: drh tags: trunk
14:22
Change the definition of SQLITE_CONFIG_SCRATCH so that at most one scratch buffer is used per thread. Use the generic heap memory allocator for the WalIterator object when running a checkpoint. check-in: 391c9b85 user: drh tags: trunk
13:41
Improved documentation and addition of source-code evidence marks for the sqlite3_config() interface. check-in: 681031a4 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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  ** Allocate space for memory structures
  */
  szScratch =
       nMaxCells*sizeof(u8*)                       /* apCell */
     + nMaxCells*sizeof(u16)                       /* szCell */
     + pBt->pageSize;                              /* aSpace1 */

  /* EVIDENCE-OF: R-37926-08392 SQLite will never request a scratch buffer
  ** that is more than 6 times the database page size, except when
  ** performing a checkpoint in WAL mode when the scratch buffer request
  ** size is a small fraction of the size of the WAL file. */
  assert( szScratch<=6*pBt->pageSize );

  apCell = sqlite3ScratchMalloc( szScratch ); 
  if( apCell==0 ){
    rc = SQLITE_NOMEM;
    goto balance_cleanup;
  }
  szCell = (u16*)&apCell[nMaxCells];
  aSpace1 = (u8*)&szCell[nMaxCells];







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  ** Allocate space for memory structures
  */
  szScratch =
       nMaxCells*sizeof(u8*)                       /* apCell */
     + nMaxCells*sizeof(u16)                       /* szCell */
     + pBt->pageSize;                              /* aSpace1 */

  /* EVIDENCE-OF: R-28375-38319 SQLite will never request a scratch buffer
  ** that is more than 6 times the database page size. */


  assert( szScratch<=6*pBt->pageSize );

  apCell = sqlite3ScratchMalloc( szScratch ); 
  if( apCell==0 ){
    rc = SQLITE_NOMEM;
    goto balance_cleanup;
  }
  szCell = (u16*)&apCell[nMaxCells];
  aSpace1 = (u8*)&szCell[nMaxCells];

Changes to src/malloc.c.

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    }
    sqlite3MemdebugSetType(p, MEMTYPE_SCRATCH);
  }
  assert( sqlite3_mutex_notheld(mem0.mutex) );


#if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
  /* Verify that no more than two scratch allocations per thread
  ** are outstanding at one time.  (This is only checked in the
  ** single-threaded case since checking in the multi-threaded case
  ** would be much more complicated.) */

  assert( scratchAllocOut<=1 );
  if( p ) scratchAllocOut++;
#endif

  return p;
}
void sqlite3ScratchFree(void *p){
  if( p ){







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    }
    sqlite3MemdebugSetType(p, MEMTYPE_SCRATCH);
  }
  assert( sqlite3_mutex_notheld(mem0.mutex) );


#if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
  /* EVIDENCE-OF: R-12970-05880 SQLite will not use more than one scratch
  ** buffers per thread.
  **
  ** This can only be checked in single-threaded mode.
  */
  assert( scratchAllocOut==0 );
  if( p ) scratchAllocOut++;
#endif

  return p;
}
void sqlite3ScratchFree(void *p){
  if( p ){

Changes to src/sqlite.h.in.

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** that SQLite can use for scratch memory.  ^(There are three arguments
** to SQLITE_CONFIG_SCRATCH:  A pointer an 8-byte
** aligned memory buffer from which the scratch allocations will be
** drawn, the size of each scratch allocation (sz),
** and the maximum number of scratch allocations (N).)^
** The first argument must be a pointer to an 8-byte aligned buffer
** of at least sz*N bytes of memory.
** ^SQLite will not use more than two scratch buffers per thread and not
** more than one scratch buffer per thread when not performing
** a [checkpoint] in [WAL mode].
** ^SQLite will never request a scratch buffer that is more than 6
** times the database page size, except when performing a [checkpoint]
** in [WAL mode] when the scratch buffer request size is a small fraction
** of the size of the WAL file.
** ^If SQLite needs needs additional
** scratch memory beyond what is provided by this configuration option, then 
** [sqlite3_malloc()] will be used to obtain the memory needed.<p>
** ^When the application provides any amount of scratch memory using
** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
** [sqlite3_malloc|heap allocations].
** This can help [Robson proof|prevent memory allocation failures] due to heap







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** that SQLite can use for scratch memory.  ^(There are three arguments
** to SQLITE_CONFIG_SCRATCH:  A pointer an 8-byte
** aligned memory buffer from which the scratch allocations will be
** drawn, the size of each scratch allocation (sz),
** and the maximum number of scratch allocations (N).)^
** The first argument must be a pointer to an 8-byte aligned buffer
** of at least sz*N bytes of memory.
** ^SQLite will not use more than one scratch buffers per thread.


** ^SQLite will never request a scratch buffer that is more than 6
** times the database page size.


** ^If SQLite needs needs additional
** scratch memory beyond what is provided by this configuration option, then 
** [sqlite3_malloc()] will be used to obtain the memory needed.<p>
** ^When the application provides any amount of scratch memory using
** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
** [sqlite3_malloc|heap allocations].
** This can help [Robson proof|prevent memory allocation failures] due to heap

Changes to src/wal.c.

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#endif
}

/* 
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3ScratchFree(p);
}

/*
** Construct a WalInterator object that can be used to loop over all 
** pages in the WAL in ascending order. The caller must hold the checkpoint
** lock.
**
................................................................................
  iLast = pWal->hdr.mxFrame;

  /* Allocate space for the WalIterator object. */
  nSegment = walFramePage(iLast) + 1;
  nByte = sizeof(WalIterator) 
        + (nSegment-1)*sizeof(struct WalSegment)
        + iLast*sizeof(ht_slot);
  p = (WalIterator *)sqlite3ScratchMalloc(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }
  memset(p, 0, nByte);
  p->nSegment = nSegment;

  /* Allocate temporary space used by the merge-sort routine. This block
  ** of memory will be freed before this function returns.
  */
  aTmp = (ht_slot *)sqlite3ScratchMalloc(
      sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
  );
  if( !aTmp ){
    rc = SQLITE_NOMEM;
  }

  for(i=0; rc==SQLITE_OK && i<nSegment; i++){
................................................................................
      walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);
      p->aSegment[i].iZero = iZero;
      p->aSegment[i].nEntry = nEntry;
      p->aSegment[i].aIndex = aIndex;
      p->aSegment[i].aPgno = (u32 *)aPgno;
    }
  }
  sqlite3ScratchFree(aTmp);

  if( rc!=SQLITE_OK ){
    walIteratorFree(p);
  }
  *pp = p;
  return rc;
}







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#endif
}

/* 
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);
}

/*
** Construct a WalInterator object that can be used to loop over all 
** pages in the WAL in ascending order. The caller must hold the checkpoint
** lock.
**
................................................................................
  iLast = pWal->hdr.mxFrame;

  /* Allocate space for the WalIterator object. */
  nSegment = walFramePage(iLast) + 1;
  nByte = sizeof(WalIterator) 
        + (nSegment-1)*sizeof(struct WalSegment)
        + iLast*sizeof(ht_slot);
  p = (WalIterator *)sqlite3_malloc(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }
  memset(p, 0, nByte);
  p->nSegment = nSegment;

  /* Allocate temporary space used by the merge-sort routine. This block
  ** of memory will be freed before this function returns.
  */
  aTmp = (ht_slot *)sqlite3_malloc(
      sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
  );
  if( !aTmp ){
    rc = SQLITE_NOMEM;
  }

  for(i=0; rc==SQLITE_OK && i<nSegment; i++){
................................................................................
      walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);
      p->aSegment[i].iZero = iZero;
      p->aSegment[i].nEntry = nEntry;
      p->aSegment[i].aIndex = aIndex;
      p->aSegment[i].aPgno = (u32 *)aPgno;
    }
  }
  sqlite3_free(aTmp);

  if( rc!=SQLITE_OK ){
    walIteratorFree(p);
  }
  *pp = p;
  return rc;
}