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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Avoid using uninitialized variables after failures in the merge sort code.
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SHA1: 2869ed28299b1c9f355ecc24635830f7f1249126
User & Date: drh 2011-08-31 23:57:22
Context
2011-09-02
15:08
Remove unused local variable. check-in: 61bda876 user: mistachkin tags: trunk
2011-09-01
15:32
Experimental code-generator changes to utilize new opcodes for sorting. check-in: bab2e560 user: drh tags: merge-sort
2011-08-31
23:57
Avoid using uninitialized variables after failures in the merge sort code. check-in: 2869ed28 user: drh tags: trunk
21:01
Formerly, we enabled fdatasync() on linux only. But now we learn that fdatasync() is not supported on Android. So we disable fdatasync() on Linux too. It can be reenabled at compile-time for those who really need it. check-in: 70b5b309 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/vdbesort.c.

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*/
static int vdbeSorterIterNext(
  sqlite3 *db,                    /* Database handle (for sqlite3DbMalloc() ) */
  VdbeSorterIter *pIter           /* Iterator to advance */
){
  int rc;                         /* Return Code */
  int nRead;                      /* Number of bytes read */
  int nRec;                       /* Size of record in bytes */
  int iOff;                       /* Size of serialized size varint in bytes */

  nRead = pIter->iEof - pIter->iReadOff;
  if( nRead>5 ) nRead = 5;
  if( nRead<=0 ){
    /* This is an EOF condition */
    vdbeSorterIterZero(db, pIter);
    return SQLITE_OK;
  }

  rc = sqlite3OsRead(pIter->pFile, pIter->aAlloc, nRead, pIter->iReadOff);

  iOff = getVarint32(pIter->aAlloc, nRec);

  if( rc==SQLITE_OK && (iOff+nRec)>nRead ){
    int nRead2;                   /* Number of extra bytes to read */
    if( (iOff+nRec)>pIter->nAlloc ){
      int nNew = pIter->nAlloc*2;
      while( (iOff+nRec)>nNew ) nNew = nNew*2;
      pIter->aAlloc = sqlite3DbReallocOrFree(db, pIter->aAlloc, nNew);
      if( !pIter->aAlloc ) return SQLITE_NOMEM;
      pIter->nAlloc = nNew;
    }

    nRead2 = iOff + nRec - nRead;
    rc = sqlite3OsRead(
        pIter->pFile, &pIter->aAlloc[nRead], nRead2, pIter->iReadOff+nRead
    );
  }


  assert( nRec>0 || rc!=SQLITE_OK );
  pIter->iReadOff += iOff+nRec;
  pIter->nKey = nRec;
  pIter->aKey = &pIter->aAlloc[iOff];
  return rc;
}

/*
................................................................................
){
  VdbeSorter *pSorter = pCsr->pSorter;
  int rc = SQLITE_OK;             /* Return code */
  int i;                          /* Used to iterator through aIter[] */
  i64 nByte = 0;                  /* Total bytes in all opened PMAs */

  /* Initialize the iterators. */
  for(i=0; rc==SQLITE_OK && i<SORTER_MAX_MERGE_COUNT; i++){
    VdbeSorterIter *pIter = &pSorter->aIter[i];
    rc = vdbeSorterIterInit(db, pSorter, pSorter->iReadOff, pIter, &nByte);
    pSorter->iReadOff = pIter->iEof;
    assert( pSorter->iReadOff<=pSorter->iWriteOff || rc!=SQLITE_OK );
    if( pSorter->iReadOff>=pSorter->iWriteOff ) break;
  }

  /* Initialize the aTree[] array. */
  for(i=pSorter->nTree-1; rc==SQLITE_OK && i>0; i--){
    rc = vdbeSorterDoCompare(pCsr, i);
  }








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*/
static int vdbeSorterIterNext(
  sqlite3 *db,                    /* Database handle (for sqlite3DbMalloc() ) */
  VdbeSorterIter *pIter           /* Iterator to advance */
){
  int rc;                         /* Return Code */
  int nRead;                      /* Number of bytes read */
  int nRec = 0;                   /* Size of record in bytes */
  int iOff = 0;                   /* Size of serialized size varint in bytes */

  nRead = pIter->iEof - pIter->iReadOff;
  if( nRead>5 ) nRead = 5;
  if( nRead<=0 ){
    /* This is an EOF condition */
    vdbeSorterIterZero(db, pIter);
    return SQLITE_OK;
  }

  rc = sqlite3OsRead(pIter->pFile, pIter->aAlloc, nRead, pIter->iReadOff);
  if( rc==SQLITE_OK ){
    iOff = getVarint32(pIter->aAlloc, nRec);

    if( (iOff+nRec)>nRead ){
      int nRead2;                   /* Number of extra bytes to read */
      if( (iOff+nRec)>pIter->nAlloc ){
        int nNew = pIter->nAlloc*2;
        while( (iOff+nRec)>nNew ) nNew = nNew*2;
        pIter->aAlloc = sqlite3DbReallocOrFree(db, pIter->aAlloc, nNew);
        if( !pIter->aAlloc ) return SQLITE_NOMEM;
        pIter->nAlloc = nNew;
      }
  
      nRead2 = iOff + nRec - nRead;
      rc = sqlite3OsRead(
          pIter->pFile, &pIter->aAlloc[nRead], nRead2, pIter->iReadOff+nRead
      );
    }
  }

  assert( rc!=SQLITE_OK || nRec>0 );
  pIter->iReadOff += iOff+nRec;
  pIter->nKey = nRec;
  pIter->aKey = &pIter->aAlloc[iOff];
  return rc;
}

/*
................................................................................
){
  VdbeSorter *pSorter = pCsr->pSorter;
  int rc = SQLITE_OK;             /* Return code */
  int i;                          /* Used to iterator through aIter[] */
  i64 nByte = 0;                  /* Total bytes in all opened PMAs */

  /* Initialize the iterators. */
  for(i=0; i<SORTER_MAX_MERGE_COUNT; i++){
    VdbeSorterIter *pIter = &pSorter->aIter[i];
    rc = vdbeSorterIterInit(db, pSorter, pSorter->iReadOff, pIter, &nByte);
    pSorter->iReadOff = pIter->iEof;
    assert( rc!=SQLITE_OK || pSorter->iReadOff<=pSorter->iWriteOff );
    if( rc!=SQLITE_OK || pSorter->iReadOff>=pSorter->iWriteOff ) break;
  }

  /* Initialize the aTree[] array. */
  for(i=pSorter->nTree-1; rc==SQLITE_OK && i>0; i--){
    rc = vdbeSorterDoCompare(pCsr, i);
  }