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Overview
Comment:Small simplification to the prepare statement opcode memory reuse logic. Easier to read, and slightly smaller and faster.
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SHA1: 8a1deae497edf3fa43fa96152d140405398c5ed6
User & Date: drh 2016-01-25 02:15:02
Context
2016-01-25
13:55
Add the SQLITE_EXTRA_DURABLE compile-time option. check-in: 30671345 user: drh tags: trunk
02:15
Small simplification to the prepare statement opcode memory reuse logic. Easier to read, and slightly smaller and faster. check-in: 8a1deae4 user: drh tags: trunk
01:07
Small simplification and performance improvement in memsys5Free(). check-in: 0a9cff5c user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/vdbeaux.c.

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    }
    z[j] = 0;
    sqlite3IoTrace("SQL %s\n", z);
  }
}
#endif /* !SQLITE_OMIT_TRACE && SQLITE_ENABLE_IOTRACE */

/*
** Allocate space from a fixed size buffer and return a pointer to
** that space.  If insufficient space is available, return NULL.
**
** The pBuf parameter is the initial value of a pointer which will
** receive the new memory.  pBuf is normally NULL.  If pBuf is not
** NULL, it means that memory space has already been allocated and that
** this routine should not allocate any new memory.  When pBuf is not
** NULL simply return pBuf.  Only allocate new memory space when pBuf
** is NULL.
**
** nByte is the number of bytes of space needed.
**
** pFrom points to *pnFrom bytes of available space.  New space is allocated
** from the end of the pFrom buffer and *pnFrom is decremented.
**
** *pnNeeded is a counter of the number of bytes of space that have failed
** to allocate.  If there is insufficient space in pFrom to satisfy the
** request, then increment *pnNeeded by the amount of the request.
*/
static void *allocSpace(
  void *pBuf,          /* Where return pointer will be stored */
  int nByte,           /* Number of bytes to allocate */
  u8 *pFrom,           /* Memory available for allocation */
  int *pnFrom,         /* IN/OUT: Space available at pFrom */
  int *pnNeeded        /* If allocation cannot be made, increment *pnByte */
){
  assert( EIGHT_BYTE_ALIGNMENT(pFrom) );
  if( pBuf==0 ){
    nByte = ROUND8(nByte);
    if( nByte <= *pnFrom ){
      *pnFrom -= nByte;
      pBuf = &pFrom[*pnFrom];
    }else{
      *pnNeeded += nByte;


    }
  }
  assert( EIGHT_BYTE_ALIGNMENT(pBuf) );
  return pBuf;
}

/*
................................................................................
  sqlite3 *db;                   /* The database connection */
  int nVar;                      /* Number of parameters */
  int nMem;                      /* Number of VM memory registers */
  int nCursor;                   /* Number of cursors required */
  int nArg;                      /* Number of arguments in subprograms */
  int nOnce;                     /* Number of OP_Once instructions */
  int n;                         /* Loop counter */
  int nFree;                     /* Available free space */
  u8 *zCsr;                      /* Memory available for allocation */
  int nByte;                     /* How much extra memory is needed */

  assert( p!=0 );
  assert( p->nOp>0 );
  assert( pParse!=0 );
  assert( p->magic==VDBE_MAGIC_INIT );
  assert( pParse==p->pParse );
  db = p->db;
................................................................................
  nCursor = pParse->nTab;
  nArg = pParse->nMaxArg;
  nOnce = pParse->nOnce;
  if( nOnce==0 ) nOnce = 1; /* Ensure at least one byte in p->aOnceFlag[] */
  
  /* For each cursor required, also allocate a memory cell. Memory
  ** cells (nMem+1-nCursor)..nMem, inclusive, will never be used by
  ** the vdbe program. Instead they are used to allocate space for
  ** VdbeCursor/BtCursor structures. The blob of memory associated with 
  ** cursor 0 is stored in memory cell nMem. Memory cell (nMem-1)
  ** stores the blob of memory associated with cursor 1, etc.
  **
  ** See also: allocateCursor().
  */
  nMem += nCursor;

  /* zCsr will initially point to nFree bytes of unused space at the
  ** end of the opcode array, p->aOp.  The computation of nFree is
  ** conservative - it might be smaller than the true number of free
  ** bytes, but never larger.  nFree must be a multiple of 8 - it is
  ** rounded down if is not.
  */
  n = ROUND8(sizeof(Op)*p->nOp);              /* Bytes of opcode space used */
  zCsr = &((u8*)p->aOp)[n];                   /* Unused opcode space */
  assert( EIGHT_BYTE_ALIGNMENT(zCsr) );
  nFree = ROUNDDOWN8(pParse->szOpAlloc - n);  /* Bytes of unused space */
  assert( nFree>=0 );
  if( nFree>0 ){
    memset(zCsr, 0, nFree);

    assert( EIGHT_BYTE_ALIGNMENT(&zCsr[nFree]) );
  }

  resolveP2Values(p, &nArg);
  p->usesStmtJournal = (u8)(pParse->isMultiWrite && pParse->mayAbort);
  if( pParse->explain && nMem<10 ){
    nMem = 10;
  }
  p->expired = 0;

  /* Memory for registers, parameters, cursor, etc, is allocated in two
  ** passes.  On the first pass, we try to reuse unused space at the 
  ** end of the opcode array.  If we are unable to satisfy all memory
  ** requirements by reusing the opcode array tail, then the second
  ** pass will fill in the rest using a fresh allocation.  
  **
  ** This two-pass approach that reuses as much memory as possible from
  ** the leftover space at the end of the opcode array can significantly
  ** reduce the amount of memory held by a prepared statement.
  */
  do {
    nByte = 0;
    p->aMem = allocSpace(p->aMem, nMem*sizeof(Mem), zCsr, &nFree, &nByte);
    p->aVar = allocSpace(p->aVar, nVar*sizeof(Mem), zCsr, &nFree, &nByte);
    p->apArg = allocSpace(p->apArg, nArg*sizeof(Mem*), zCsr, &nFree, &nByte);
    p->apCsr = allocSpace(p->apCsr, nCursor*sizeof(VdbeCursor*),
                          zCsr, &nFree, &nByte);
    p->aOnceFlag = allocSpace(p->aOnceFlag, nOnce, zCsr, &nFree, &nByte);
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
    p->anExec = allocSpace(p->anExec, p->nOp*sizeof(i64), zCsr, &nFree, &nByte);

#endif
    if( nByte ){

      p->pFree = sqlite3DbMallocZero(db, nByte);
    }
    zCsr = p->pFree;
    nFree = nByte;
  }while( nByte && !db->mallocFailed );

  p->nCursor = nCursor;
  p->nOnceFlag = nOnce;
  if( p->aVar ){
    p->nVar = (ynVar)nVar;
    for(n=0; n<nVar; n++){
      p->aVar[n].flags = MEM_Null;







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    }
    z[j] = 0;
    sqlite3IoTrace("SQL %s\n", z);
  }
}
#endif /* !SQLITE_OMIT_TRACE && SQLITE_ENABLE_IOTRACE */

/* An instance of this object describes bulk memory available for use
** by subcomponents of a prepared statement.  Space is allocated out
** of a ReusableSpace object by the allocSpace() routine below.
*/
struct ReusableSpace {
  u8 *pSpace;          /* Available memory */
  int nFree;           /* Bytes of available memory */
  int nNeeded;         /* Total bytes that could not be allocated */
};

/* Try to allocate nByte bytes of 8-byte aligned bulk memory for pBuf
** from the ReusableSpace object.  Return a pointer to the allocated
** memory on success.  If insufficient memory is available in the
** ReusableSpace object, increase the ReusableSpace.nNeeded
** value by the amount needed and return NULL.
**
** If pBuf is not initially NULL, that means that the memory has already
** been allocated by a prior call to this routine, so just return a copy
** of pBuf and leave ReusableSpace unchanged.
**
** This allocator is employed to repurpose unused slots at the end of the
** opcode array of prepared state for other memory needs of the prepared
** statement.
*/
static void *allocSpace(
  struct ReusableSpace *p,  /* Bulk memory available for allocation */
  void *pBuf,               /* Pointer to a prior allocation */
  int nByte                 /* Bytes of memory needed */
){
  assert( EIGHT_BYTE_ALIGNMENT(p->pSpace) );
  if( pBuf==0 ){
    nByte = ROUND8(nByte);
    if( nByte <= p->nFree ){
      p->nFree -= nByte;
      pBuf = &p->pSpace[p->nFree];
    }else{
      p->nNeeded += nByte;
    }
  }
  assert( EIGHT_BYTE_ALIGNMENT(pBuf) );
  return pBuf;
}

/*
................................................................................
  sqlite3 *db;                   /* The database connection */
  int nVar;                      /* Number of parameters */
  int nMem;                      /* Number of VM memory registers */
  int nCursor;                   /* Number of cursors required */
  int nArg;                      /* Number of arguments in subprograms */
  int nOnce;                     /* Number of OP_Once instructions */
  int n;                         /* Loop counter */
  struct ReusableSpace x;        /* Reusable bulk memory */



  assert( p!=0 );
  assert( p->nOp>0 );
  assert( pParse!=0 );
  assert( p->magic==VDBE_MAGIC_INIT );
  assert( pParse==p->pParse );
  db = p->db;
................................................................................
  nCursor = pParse->nTab;
  nArg = pParse->nMaxArg;
  nOnce = pParse->nOnce;
  if( nOnce==0 ) nOnce = 1; /* Ensure at least one byte in p->aOnceFlag[] */
  
  /* For each cursor required, also allocate a memory cell. Memory
  ** cells (nMem+1-nCursor)..nMem, inclusive, will never be used by
  ** the vdbe program. Instead they are used to allocate memory for
  ** VdbeCursor/BtCursor structures. The blob of memory associated with 
  ** cursor 0 is stored in memory cell nMem. Memory cell (nMem-1)
  ** stores the blob of memory associated with cursor 1, etc.
  **
  ** See also: allocateCursor().
  */
  nMem += nCursor;

  /* Figure out how much reusable memory is available at the end of the
  ** opcode array.  This extra memory will be reallocated for other elements
  ** of the prepared statement.


  */
  n = ROUND8(sizeof(Op)*p->nOp);              /* Bytes of opcode memory used */
  x.pSpace = &((u8*)p->aOp)[n];               /* Unused opcode memory */
  assert( EIGHT_BYTE_ALIGNMENT(x.pSpace) );
  x.nFree = ROUNDDOWN8(pParse->szOpAlloc - n);  /* Bytes of unused memory */
  assert( x.nFree>=0 );
  if( x.nFree>0 ){

    memset(x.pSpace, 0, x.nFree);
    assert( EIGHT_BYTE_ALIGNMENT(&x.pSpace[x.nFree]) );
  }

  resolveP2Values(p, &nArg);
  p->usesStmtJournal = (u8)(pParse->isMultiWrite && pParse->mayAbort);
  if( pParse->explain && nMem<10 ){
    nMem = 10;
  }
  p->expired = 0;

  /* Memory for registers, parameters, cursor, etc, is allocated in one or two
  ** passes.  On the first pass, we try to reuse unused memory at the 
  ** end of the opcode array.  If we are unable to satisfy all memory
  ** requirements by reusing the opcode array tail, then the second
  ** pass will fill in the remainder using a fresh memory allocation.  
  **
  ** This two-pass approach that reuses as much memory as possible from
  ** the leftover memory at the end of the opcode array.  This can significantly
  ** reduce the amount of memory held by a prepared statement.
  */
  do {
    x.nNeeded = 0;
    p->aMem = allocSpace(&x, p->aMem, nMem*sizeof(Mem));
    p->aVar = allocSpace(&x, p->aVar, nVar*sizeof(Mem));
    p->apArg = allocSpace(&x, p->apArg, nArg*sizeof(Mem*));
    p->apCsr = allocSpace(&x, p->apCsr, nCursor*sizeof(VdbeCursor*));

    p->aOnceFlag = allocSpace(&x, p->aOnceFlag, nOnce);
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS

    p->anExec = allocSpace(&x, p->anExec, p->nOp*sizeof(i64));
#endif

    if( x.nNeeded==0 ) break;
    x.pSpace = p->pFree = sqlite3DbMallocZero(db, x.nNeeded);


    x.nFree = x.nNeeded;
  }while( !db->mallocFailed );

  p->nCursor = nCursor;
  p->nOnceFlag = nOnce;
  if( p->aVar ){
    p->nVar = (ynVar)nVar;
    for(n=0; n<nVar; n++){
      p->aVar[n].flags = MEM_Null;