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Overview
Comment:Simplification to the insertCell() routine in btree.c, resulting in a performance boost and a very small size decrease. It turns out that the extra work involved in sometimes avoiding an memcpy() of the first four bytes of a record takes more time than just unconditionally copying those four bytes.
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SHA1: 66de15580d3c289601e67debfe1edee286f4db5f
User & Date: drh 2014-10-11 17:22:55
Context
2014-10-11
23:31
Performance optimization and very slight size reduction for OP_Column. check-in: 869c30e4 user: drh tags: trunk
17:22
Simplification to the insertCell() routine in btree.c, resulting in a performance boost and a very small size decrease. It turns out that the extra work involved in sometimes avoiding an memcpy() of the first four bytes of a record takes more time than just unconditionally copying those four bytes. check-in: 66de1558 user: drh tags: trunk
10:52
Require the SQLITE_ENABLE_RTREE compile-time option in speedtest1.c in order to enable the R-Tree tests. check-in: 5d29a033 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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** If the cell content will fit on the page, then put it there.  If it
** will not fit, then make a copy of the cell content into pTemp if
** pTemp is not null.  Regardless of pTemp, allocate a new entry
** in pPage->apOvfl[] and make it point to the cell content (either
** in pTemp or the original pCell) and also record its index. 
** Allocating a new entry in pPage->aCell[] implies that 
** pPage->nOverflow is incremented.
**
** If nSkip is non-zero, then do not copy the first nSkip bytes of the
** cell. The caller will overwrite them after this function returns. If
** nSkip is non-zero, then pCell may not point to an invalid memory location 
** (but pCell+nSkip is always valid).
*/
static void insertCell(
  MemPage *pPage,   /* Page into which we are copying */
  int i,            /* New cell becomes the i-th cell of the page */
  u8 *pCell,        /* Content of the new cell */
  int sz,           /* Bytes of content in pCell */
  u8 *pTemp,        /* Temp storage space for pCell, if needed */
................................................................................
){
  int idx = 0;      /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  int end;          /* First byte past the last cell pointer in data[] */
  int ins;          /* Index in data[] where new cell pointer is inserted */
  int cellOffset;   /* Address of first cell pointer in data[] */
  u8 *data;         /* The content of the whole page */
  int nSkip = (iChild ? 4 : 0);

  if( *pRC ) return;

  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
  assert( MX_CELL(pPage->pBt)<=10921 );
  assert( pPage->nCell<=MX_CELL(pPage->pBt) || CORRUPT_DB );
  assert( pPage->nOverflow<=ArraySize(pPage->apOvfl) );
................................................................................
  ** malformed cell from a leaf page to an interior page, if the cell size
  ** wanted to be less than 4 but got rounded up to 4 on the leaf, then size
  ** might be less than 8 (leaf-size + pointer) on the interior node.  Hence
  ** the term after the || in the following assert(). */
  assert( sz==cellSizePtr(pPage, pCell) || (sz==8 && iChild>0) );
  if( pPage->nOverflow || sz+2>pPage->nFree ){
    if( pTemp ){
      memcpy(pTemp+nSkip, pCell+nSkip, sz-nSkip);
      pCell = pTemp;
    }
    if( iChild ){
      put4byte(pCell, iChild);
    }
    j = pPage->nOverflow++;
    assert( j<(int)(sizeof(pPage->apOvfl)/sizeof(pPage->apOvfl[0])) );
................................................................................
    if( rc ){ *pRC = rc; return; }
    /* The allocateSpace() routine guarantees the following two properties
    ** if it returns success */
    assert( idx >= end+2 );
    assert( idx+sz <= (int)pPage->pBt->usableSize );
    pPage->nCell++;
    pPage->nFree -= (u16)(2 + sz);
    memcpy(&data[idx+nSkip], pCell+nSkip, sz-nSkip);
    if( iChild ){
      put4byte(&data[idx], iChild);
    }
    memmove(&data[ins+2], &data[ins], end-ins);
    put2byte(&data[ins], idx);
    put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
#ifndef SQLITE_OMIT_AUTOVACUUM







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** If the cell content will fit on the page, then put it there.  If it
** will not fit, then make a copy of the cell content into pTemp if
** pTemp is not null.  Regardless of pTemp, allocate a new entry
** in pPage->apOvfl[] and make it point to the cell content (either
** in pTemp or the original pCell) and also record its index. 
** Allocating a new entry in pPage->aCell[] implies that 
** pPage->nOverflow is incremented.





*/
static void insertCell(
  MemPage *pPage,   /* Page into which we are copying */
  int i,            /* New cell becomes the i-th cell of the page */
  u8 *pCell,        /* Content of the new cell */
  int sz,           /* Bytes of content in pCell */
  u8 *pTemp,        /* Temp storage space for pCell, if needed */
................................................................................
){
  int idx = 0;      /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  int end;          /* First byte past the last cell pointer in data[] */
  int ins;          /* Index in data[] where new cell pointer is inserted */
  int cellOffset;   /* Address of first cell pointer in data[] */
  u8 *data;         /* The content of the whole page */


  if( *pRC ) return;

  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
  assert( MX_CELL(pPage->pBt)<=10921 );
  assert( pPage->nCell<=MX_CELL(pPage->pBt) || CORRUPT_DB );
  assert( pPage->nOverflow<=ArraySize(pPage->apOvfl) );
................................................................................
  ** malformed cell from a leaf page to an interior page, if the cell size
  ** wanted to be less than 4 but got rounded up to 4 on the leaf, then size
  ** might be less than 8 (leaf-size + pointer) on the interior node.  Hence
  ** the term after the || in the following assert(). */
  assert( sz==cellSizePtr(pPage, pCell) || (sz==8 && iChild>0) );
  if( pPage->nOverflow || sz+2>pPage->nFree ){
    if( pTemp ){
      memcpy(pTemp, pCell, sz);
      pCell = pTemp;
    }
    if( iChild ){
      put4byte(pCell, iChild);
    }
    j = pPage->nOverflow++;
    assert( j<(int)(sizeof(pPage->apOvfl)/sizeof(pPage->apOvfl[0])) );
................................................................................
    if( rc ){ *pRC = rc; return; }
    /* The allocateSpace() routine guarantees the following two properties
    ** if it returns success */
    assert( idx >= end+2 );
    assert( idx+sz <= (int)pPage->pBt->usableSize );
    pPage->nCell++;
    pPage->nFree -= (u16)(2 + sz);
    memcpy(&data[idx], pCell, sz);
    if( iChild ){
      put4byte(&data[idx], iChild);
    }
    memmove(&data[ins+2], &data[ins], end-ins);
    put2byte(&data[ins], idx);
    put2byte(&data[pPage->hdrOffset+3], pPage->nCell);
#ifndef SQLITE_OMIT_AUTOVACUUM