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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Change the sqlite3VdbeMemGrow() routine so that it no longer guarantees a minimum size of 32 bytes. That minimum is no longer required, and without the extra check for the minimum size, the routine runs faster.
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SHA3-256: 5c499da8a4d0babc56883aa362ae124772fd9214a51169a88a5dee523d051658
User & Date: drh 2019-02-08 15:59:20
Context
2019-02-08
17:28
Further simplifications to sqlite3VdbeMemSetStr(). check-in: 1d212957 user: drh tags: trunk
15:59
Change the sqlite3VdbeMemGrow() routine so that it no longer guarantees a minimum size of 32 bytes. That minimum is no longer required, and without the extra check for the minimum size, the routine runs faster. check-in: 5c499da8 user: drh tags: trunk
14:55
Give the sqlite3 object a pointer to the current Parse so that if an OOM occurs, it can automatically set the Parse.rc value to SQLITE_NOMEM. This avoids a frequent extra test of db.mallocFailed in the innermost parser loop. check-in: 5c663804 user: drh tags: trunk
Changes
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Changes to src/vdbemem.c.

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  assert(rc==SQLITE_OK    || pMem->enc!=desiredEnc);
  assert(rc==SQLITE_NOMEM || pMem->enc==desiredEnc);
  return rc;
#endif
}

/*
** Make sure pMem->z points to a writable allocation of at least 
** min(n,32) bytes.
**
** If the bPreserve argument is true, then copy of the content of
** pMem->z into the new allocation.  pMem must be either a string or
** blob if bPreserve is true.  If bPreserve is false, any prior content
** in pMem->z is discarded.
*/
SQLITE_NOINLINE int sqlite3VdbeMemGrow(Mem *pMem, int n, int bPreserve){
................................................................................
  /* If the bPreserve flag is set to true, then the memory cell must already
  ** contain a valid string or blob value.  */
  assert( bPreserve==0 || pMem->flags&(MEM_Blob|MEM_Str) );
  testcase( bPreserve && pMem->z==0 );

  assert( pMem->szMalloc==0
       || pMem->szMalloc==sqlite3DbMallocSize(pMem->db, pMem->zMalloc) );
  if( n<32 ) n = 32;
  if( pMem->szMalloc>0 && bPreserve && pMem->z==pMem->zMalloc ){
    pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->db, pMem->z, n);
    bPreserve = 0;
  }else{
    if( pMem->szMalloc>0 ) sqlite3DbFreeNN(pMem->db, pMem->zMalloc);
    pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
  }







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  assert(rc==SQLITE_OK    || pMem->enc!=desiredEnc);
  assert(rc==SQLITE_NOMEM || pMem->enc==desiredEnc);
  return rc;
#endif
}

/*
** Make sure pMem->z points to a writable allocation of at least n bytes.

**
** If the bPreserve argument is true, then copy of the content of
** pMem->z into the new allocation.  pMem must be either a string or
** blob if bPreserve is true.  If bPreserve is false, any prior content
** in pMem->z is discarded.
*/
SQLITE_NOINLINE int sqlite3VdbeMemGrow(Mem *pMem, int n, int bPreserve){
................................................................................
  /* If the bPreserve flag is set to true, then the memory cell must already
  ** contain a valid string or blob value.  */
  assert( bPreserve==0 || pMem->flags&(MEM_Blob|MEM_Str) );
  testcase( bPreserve && pMem->z==0 );

  assert( pMem->szMalloc==0
       || pMem->szMalloc==sqlite3DbMallocSize(pMem->db, pMem->zMalloc) );

  if( pMem->szMalloc>0 && bPreserve && pMem->z==pMem->zMalloc ){
    pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->db, pMem->z, n);
    bPreserve = 0;
  }else{
    if( pMem->szMalloc>0 ) sqlite3DbFreeNN(pMem->db, pMem->zMalloc);
    pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
  }