*/

/*
** For each row modified during a session, there exists a single instance of
** this structure stored in a SessionTable.aChange[] hash table.
*/
struct SessionChange {
  int bInsert;                    /* True if row was inserted this session */
  int bIndirect;                  /* True if this change is "indirect" */
  int nRecord;                    /* Number of bytes in buffer aRecord[] */
  u8 *aRecord;                    /* Buffer containing old.* record */
  SessionChange *pNext;           /* For hash-table collisions */
};

/*
................................................................................
    if( aBuf ) aBuf[0] = '\0';
  }

  *pnWrite += nByte;
  return SQLITE_OK;
}
















#define HASH_APPEND(hash, add) ((hash) << 3) ^ (hash) ^ (unsigned int)(add)





static unsigned int sessionHashAppendI64(unsigned int h, i64 i){
  h = HASH_APPEND(h, i & 0xFFFFFFFF);
  return HASH_APPEND(h, (i>>32)&0xFFFFFFFF);
}





static unsigned int sessionHashAppendBlob(unsigned int h, int n, const u8 *z){
  int i;
  for(i=0; i<n; i++) h = HASH_APPEND(h, z[i]);
  return h;
}









/*
** This function may only be called from within a pre-update callback.
** It calculates a hash based on the primary key values of the old.* or 
** new.* row currently available. The value returned is guaranteed to
** be less than pTab->nBucket.





*/
static unsigned int sessionPreupdateHash(
  sqlite3 *db,                    /* Database handle */
  SessionTable *pTab,             /* Session table handle */
  int bNew,                       /* True to hash the new.* PK */
  int *piHash,                    /* OUT: Hash value */
  int *pbNullPK
){
  unsigned int h = 0;             /* Hash value to return */
  int i;                          /* Used to iterate through columns */

  assert( *pbNullPK==0 );
  assert( pTab->nCol==sqlite3_preupdate_count(db) );
  for(i=0; i<pTab->nCol; i++){
................................................................................
        rc = sqlite3_preupdate_new(db, i, &pVal);
      }else{
        rc = sqlite3_preupdate_old(db, i, &pVal);
      }
      if( rc!=SQLITE_OK ) return rc;

      eType = sqlite3_value_type(pVal);
      h = HASH_APPEND(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        i64 iVal;
        if( eType==SQLITE_INTEGER ){
          iVal = sqlite3_value_int64(pVal);
        }else{
          double rVal = sqlite3_value_double(pVal);
          assert( sizeof(iVal)==8 && sizeof(rVal)==8 );
................................................................................
          z = (const u8 *)sqlite3_value_blob(pVal);
        }
        if( !z ) return SQLITE_NOMEM;
        h = sessionHashAppendBlob(h, sqlite3_value_bytes(pVal), z);
      }else{
        assert( eType==SQLITE_NULL );
        *pbNullPK = 1;
        return SQLITE_OK;
      }
    }
  }

  *piHash = (h % pTab->nChange);
  return SQLITE_OK;
}
................................................................................
  if( e==SQLITE_NULL ) return 1;
  if( e==SQLITE_INTEGER || e==SQLITE_FLOAT ) return 9;
  return sessionVarintGet(&a[1], &n) + 1 + n;
}

/*
** Based on the primary key values stored in change aRecord, calculate a
** hash key, assuming the has table has nBucket buckets. The hash keys
** calculated by this function are compatible with those calculated by
** sessionPreupdateHash().
*/
static unsigned int sessionChangeHash(
  SessionTable *pTab,             /* Table handle */
  u8 *aRecord,                    /* Change record */
  int nBucket                     /* Assume this many buckets in hash table */
................................................................................
         || eType==SQLITE_TEXT || eType==SQLITE_BLOB 
         || eType==SQLITE_NULL || eType==0 
    );
    assert( !isPK || (eType!=0 && eType!=SQLITE_NULL) );

    if( isPK ){
      a++;
      h = HASH_APPEND(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        h = sessionHashAppendI64(h, sessionGetI64(a));
        a += 8;
      }else{
        int n; 
        a += sessionVarintGet(a, &n);
        h = sessionHashAppendBlob(h, n, a);
................................................................................
    }else{
      a += sessionSerialLen(a);
    }
  }
  return (h % nBucket);
}







static int sessionChangeEqual(
  SessionTable *pTab,
  u8 *aLeft,                      /* Change record */
  u8 *aRight                      /* Change record */
){
  u8 *a1 = aLeft;
  u8 *a2 = aRight;
  int i;

  for(i=0; i<pTab->nCol; i++){
    int n1 = sessionSerialLen(a1);
    int n2 = sessionSerialLen(a2);

    if( pTab->abPK[i] && (n1!=n2 || memcmp(a1, a2, n1)) ){
      return 0;
    }
    a1 += n1;
    a2 += n2;
  }

  return 1;
}














static void sessionMergeRecord(
  u8 **paOut, 
  SessionTable *pTab, 

  u8 *aLeft,
  u8 *aRight
){
  u8 *a1 = aLeft;
  u8 *a2 = aRight;
  u8 *aOut = *paOut;
  int i;

  for(i=0; i<pTab->nCol; i++){
    int n1 = sessionSerialLen(a1);
    int n2 = sessionSerialLen(a2);
    if( *a2 ){
      memcpy(aOut, a2, n2);
      aOut += n2;
    }else{
      memcpy(aOut, a1, n1);
................................................................................
    a1 += n1;
    a2 += n2;
  }

  *paOut = aOut;
}















static u8 *sessionMergeValue(
  u8 **paOne,
  u8 **paTwo,
  int *pnVal



){
  u8 *a1 = *paOne;
  u8 *a2 = *paTwo;
  u8 *pRet = 0;
  int n1;

  assert( a1 );
................................................................................
    pRet = a1;
  }
  *paOne = &a1[n1];

  return pRet;
}





static int sessionMergeUpdate(
  u8 **paOut, 

  SessionTable *pTab, 
  u8 *aOldRecord1,
  u8 *aOldRecord2,
  u8 *aNewRecord1,
  u8 *aNewRecord2
){
  u8 *aOld1 = aOldRecord1;
  u8 *aOld2 = aOldRecord2;
  u8 *aNew1 = aNewRecord1;
  u8 *aNew2 = aNewRecord2;

  u8 *aOut = *paOut;
................................................................................
){
  int i;
  u8 *a = pChange->aRecord;

  *pbEqual = 0;

  for(i=0; i<pTab->nCol; i++){
    int eType = *a++;
    if( !pTab->abPK[i] ){
      switch( eType ){
        case SQLITE_INTEGER: 
        case SQLITE_FLOAT:
          a += 8;
          break;

        case SQLITE_TEXT: 
        case SQLITE_BLOB: {
          int n;
          a += sessionVarintGet(a, &n);
          a += n;
          break;
        }
      }
    }else{
      sqlite3_value *pVal;        /* Value returned by preupdate_new/old */
      int rc;                     /* Error code from preupdate_new/old */


      /* The following calls to preupdate_new() and preupdate_old() can not
      ** fail. This is because they cache their return values, and by the
      ** time control flows to here they have already been called once from
      ** within sessionPreupdateHash(). The first two asserts below verify
      ** this (that the method has already been called). */
      if( bNew ){
................................................................................
      }

      /* Add the change to the hash-table */
      if( pSession->bIndirect || sqlite3_preupdate_depth(pSession->db) ){
        pChange->bIndirect = 1;
      }
      pChange->nRecord = nByte;
      pChange->bInsert = (op==SQLITE_INSERT);
      pChange->pNext = pTab->apChange[iHash];
      pTab->apChange[iHash] = pChange;

    }else if( pC->bIndirect ){
      /* If the existing change is considered "indirect", but this current
      ** change is "direct", mark the change object as direct. */
      if( sqlite3_preupdate_depth(pSession->db)==0 && pSession->bIndirect==0 ){
................................................................................
      for(i=0; i<pTab->nChange && rc==SQLITE_OK; i++){
        SessionChange *p;         /* Used to iterate through changes */

        for(p=pTab->apChange[i]; rc==SQLITE_OK && p; p=p->pNext){
          rc = sessionSelectBind(pSel, nCol, abPK, p);
          if( rc!=SQLITE_OK ) continue;
          if( sqlite3_step(pSel)==SQLITE_ROW ){

            int iCol;
            if( p->bInsert ){
              sessionAppendByte(&buf, SQLITE_INSERT, &rc);
              sessionAppendByte(&buf, p->bIndirect, &rc);
              for(iCol=0; iCol<nCol; iCol++){
                sessionAppendCol(&buf, pSel, iCol, &rc);
              }
            }else{
              rc = sessionAppendUpdate(&buf, pSel, p, abPK);
            }
          }else if( !p->bInsert ){
            /* A DELETE change */
            sessionAppendByte(&buf, SQLITE_DELETE, &rc);
            sessionAppendByte(&buf, p->bIndirect, &rc);
            sessionAppendBlob(&buf, p->aRecord, p->nRecord, &rc);
          }
          if( rc==SQLITE_OK ){
            rc = sqlite3_reset(pSel);
................................................................................

  if( !pExist ){
    pNew = (SessionChange *)sqlite3_malloc(sizeof(SessionChange));
    if( !pNew ){
      return SQLITE_NOMEM;
    }
    memset(pNew, 0, sizeof(SessionChange));
    pNew->bInsert = op2;
    pNew->bIndirect = bIndirect;
    pNew->nRecord = nRec;
    pNew->aRecord = aRec;
  }else{
    int op1 = pExist->bInsert;

    /* 
    **   op1=INSERT, op2=INSERT      ->      Unsupported. Discard op2.
    **   op1=INSERT, op2=UPDATE      ->      INSERT.
    **   op1=INSERT, op2=DELETE      ->      (none)
    **
    **   op1=UPDATE, op2=INSERT      ->      Unsupported. Discard op2.
................................................................................
      memset(pNew, 0, sizeof(SessionChange));
      pNew->bIndirect = (bIndirect && pExist->bIndirect);
      aCsr = pNew->aRecord = (u8 *)&pNew[1];

      if( op1==SQLITE_INSERT ){             /* INSERT + UPDATE */
        u8 *a1 = aRec;
        assert( op2==SQLITE_UPDATE );
        pNew->bInsert = SQLITE_INSERT;
        sessionReadRecord(&a1, pTab->nCol, 0);
        sessionMergeRecord(&aCsr, pTab, pExist->aRecord, a1);
      }else if( op1==SQLITE_DELETE ){       /* DELETE + INSERT */
        assert( op2==SQLITE_INSERT );
        pNew->bInsert = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, pExist->aRecord, 0, aRec, 0) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else if( op2==SQLITE_UPDATE ){       /* UPDATE + UPDATE */
        assert( op1==SQLITE_UPDATE );
        u8 *a1 = pExist->aRecord;
        u8 *a2 = aRec;
        sessionReadRecord(&a1, pTab->nCol, 0);
        sessionReadRecord(&a2, pTab->nCol, 0);
        pNew->bInsert = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, aRec, pExist->aRecord, a1, a2) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else{                                /* UPDATE + DELETE */
        assert( op1==SQLITE_UPDATE && op2==SQLITE_DELETE );
        pNew->bInsert = SQLITE_DELETE;
        sessionMergeRecord(&aCsr, pTab, aRec, pExist->aRecord);
      }

      if( pNew ){
        pNew->nRecord = (aCsr - pNew->aRecord);
      }
      sqlite3_free(pExist);
    }
................................................................................
      int i;
      if( pTab->nEntry==0 ) continue;

      sessionAppendTableHdr(&buf, pTab, &rc);
      for(i=0; i<pTab->nChange; i++){
        SessionChange *p;
        for(p=pTab->apChange[i]; p; p=p->pNext){
          sessionAppendByte(&buf, p->bInsert, &rc);
          sessionAppendByte(&buf, p->bIndirect, &rc);
          sessionAppendBlob(&buf, p->aRecord, p->nRecord, &rc);
        }
      }
    }

    if( rc==SQLITE_OK ){

*/

/*
** For each row modified during a session, there exists a single instance of
** this structure stored in a SessionTable.aChange[] hash table.
*/
struct SessionChange {
  int op;                         /* One of UPDATE, DELETE, INSERT */
  int bIndirect;                  /* True if this change is "indirect" */
  int nRecord;                    /* Number of bytes in buffer aRecord[] */
  u8 *aRecord;                    /* Buffer containing old.* record */
  SessionChange *pNext;           /* For hash-table collisions */
};

/*
................................................................................
    if( aBuf ) aBuf[0] = '\0';
  }

  *pnWrite += nByte;
  return SQLITE_OK;
}

/*
** This macro is used to calculate hash key values for data structures. In
** order to use this macro, the entire data structure must be represented
** as a series of unsigned integers. In order to calculate a hash-key value
** for a data structure represented as three such integers, the macro may
** then be used as follows:
**
**    int hash_key_value;
**    hash_key_value = HASH_APPEND(0, <value 1>);
**    hash_key_value = HASH_APPEND(hash_key_value, <value 2>);
**    hash_key_value = HASH_APPEND(hash_key_value, <value 3>);
**
** In practice, the data structures this macro is used for are the primary
** key values of modified rows.
*/
#define HASH_APPEND(hash, add) ((hash) << 3) ^ (hash) ^ (unsigned int)(add)

/*
** Append the hash of the 64-bit integer passed as the second argument to the
** hash-key value passed as the first. Return the new hash-key value.
*/
static unsigned int sessionHashAppendI64(unsigned int h, i64 i){
  h = HASH_APPEND(h, i & 0xFFFFFFFF);
  return HASH_APPEND(h, (i>>32)&0xFFFFFFFF);
}

/*
** Append the hash of the blob passed via the second and third arguments to 
** the hash-key value passed as the first. Return the new hash-key value.
*/
static unsigned int sessionHashAppendBlob(unsigned int h, int n, const u8 *z){
  int i;
  for(i=0; i<n; i++) h = HASH_APPEND(h, z[i]);
  return h;
}

/*
** Append the hash of the data type passed as the second argument to the
** hash-key value passed as the first. Return the new hash-key value.
*/
static unsigned int sessionHashAppendType(unsigned int h, int eType){
  return HASH_APPEND(h, eType);
}

/*
** This function may only be called from within a pre-update callback.
** It calculates a hash based on the primary key values of the old.* or 
** new.* row currently available and, assuming no error occurs, writes it to
** *piHash before returning. If the primary key contains one or more NULL
** values, *pbNullPK is set to true before returning.
**
** If an error occurs, an SQLite error code is returned and the final values
** of *piHash asn *pbNullPK are undefined. Otherwise, SQLITE_OK is returned
** and the output variables are set as described above.
*/
static int sessionPreupdateHash(
  sqlite3 *db,                    /* Database handle */
  SessionTable *pTab,             /* Session table handle */
  int bNew,                       /* True to hash the new.* PK */
  int *piHash,                    /* OUT: Hash value */
  int *pbNullPK                   /* OUT: True if there are NULL values in PK */
){
  unsigned int h = 0;             /* Hash value to return */
  int i;                          /* Used to iterate through columns */

  assert( *pbNullPK==0 );
  assert( pTab->nCol==sqlite3_preupdate_count(db) );
  for(i=0; i<pTab->nCol; i++){
................................................................................
        rc = sqlite3_preupdate_new(db, i, &pVal);
      }else{
        rc = sqlite3_preupdate_old(db, i, &pVal);
      }
      if( rc!=SQLITE_OK ) return rc;

      eType = sqlite3_value_type(pVal);
      h = sessionHashAppendType(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        i64 iVal;
        if( eType==SQLITE_INTEGER ){
          iVal = sqlite3_value_int64(pVal);
        }else{
          double rVal = sqlite3_value_double(pVal);
          assert( sizeof(iVal)==8 && sizeof(rVal)==8 );
................................................................................
          z = (const u8 *)sqlite3_value_blob(pVal);
        }
        if( !z ) return SQLITE_NOMEM;
        h = sessionHashAppendBlob(h, sqlite3_value_bytes(pVal), z);
      }else{
        assert( eType==SQLITE_NULL );
        *pbNullPK = 1;

      }
    }
  }

  *piHash = (h % pTab->nChange);
  return SQLITE_OK;
}
................................................................................
  if( e==SQLITE_NULL ) return 1;
  if( e==SQLITE_INTEGER || e==SQLITE_FLOAT ) return 9;
  return sessionVarintGet(&a[1], &n) + 1 + n;
}

/*
** Based on the primary key values stored in change aRecord, calculate a
** hash key. Assume the has table has nBucket buckets. The hash keys
** calculated by this function are compatible with those calculated by
** sessionPreupdateHash().
*/
static unsigned int sessionChangeHash(
  SessionTable *pTab,             /* Table handle */
  u8 *aRecord,                    /* Change record */
  int nBucket                     /* Assume this many buckets in hash table */
................................................................................
         || eType==SQLITE_TEXT || eType==SQLITE_BLOB 
         || eType==SQLITE_NULL || eType==0 
    );
    assert( !isPK || (eType!=0 && eType!=SQLITE_NULL) );

    if( isPK ){
      a++;
      h = sessionHashAppendType(h, eType);
      if( eType==SQLITE_INTEGER || eType==SQLITE_FLOAT ){
        h = sessionHashAppendI64(h, sessionGetI64(a));
        a += 8;
      }else{
        int n; 
        a += sessionVarintGet(a, &n);
        h = sessionHashAppendBlob(h, n, a);
................................................................................
    }else{
      a += sessionSerialLen(a);
    }
  }
  return (h % nBucket);
}

/*
** Arguments aLeft and aRight are pointers to change records for table pTab.
** This function returns true if the two records apply to the same row (i.e.
** have the same values stored in the primary key columns), or false 
** otherwise.
*/
static int sessionChangeEqual(
  SessionTable *pTab,             /* Table used for PK definition */
  u8 *aLeft,                      /* Change record */
  u8 *aRight                      /* Change record */
){
  u8 *a1 = aLeft;                 /* Cursor to iterate through aLeft */
  u8 *a2 = aRight;                /* Cursor to iterate through aRight */
  int iCol;                       /* Used to iterate through table columns */

  for(iCol=0; iCol<pTab->nCol; iCol++){
    int n1 = sessionSerialLen(a1);
    int n2 = sessionSerialLen(a2);

    if( pTab->abPK[iCol] && (n1!=n2 || memcmp(a1, a2, n1)) ){
      return 0;
    }
    a1 += n1;
    a2 += n2;
  }

  return 1;
}

/*
** Arguments aLeft and aRight both point to buffers containing change
** records with nCol columns. This function "merges" the two records into
** a single records which is written to the buffer at *paOut. *paOut is
** then set to point to one byte after the last byte written before 
** returning.
**
** The merging of records is done as follows: For each column, if the 
** aRight record contains a value for the column, copy the value from
** their. Otherwise, if aLeft contains a value, copy it. If neither
** record contains a value for a given column, then neither does the
** output record.
*/
static void sessionMergeRecord(
  u8 **paOut, 

  int nCol,
  u8 *aLeft,
  u8 *aRight
){
  u8 *a1 = aLeft;                 /* Cursor used to iterate through aLeft */
  u8 *a2 = aRight;                /* Cursor used to iterate through aRight */
  u8 *aOut = *paOut;              /* Output cursor */
  int iCol;                       /* Used to iterate from 0 to nCol */

  for(iCol=0; iCol<nCol; iCol++){
    int n1 = sessionSerialLen(a1);
    int n2 = sessionSerialLen(a2);
    if( *a2 ){
      memcpy(aOut, a2, n2);
      aOut += n2;
    }else{
      memcpy(aOut, a1, n1);
................................................................................
    a1 += n1;
    a2 += n2;
  }

  *paOut = aOut;
}

/*
** This is a helper function used by sessionMergeUpdate().
**
** When this function is called, both *paOne and *paTwo point to a value 
** within a change record. Before it returns, both have been advanced so 
** as to point to the next value in the record.
**
** If, when this function is called, *paTwo points to a valid value (i.e.
** *paTwo[0] is not 0x00 - the "no value" placeholder), a copy of the *paOne
** pointer is returned and *pnVal is set to the number of bytes in the 
** serialized value. Otherwise, a copy of *paOne is returned and *pnVal
** set to the number of bytes in the value at *paOne. If *paOne points
** to the "no value" placeholder, *pnVal is set to 1.
*/
static u8 *sessionMergeValue(



  u8 **paOne,                     /* IN/OUT: Left-hand buffer pointer */
  u8 **paTwo,                     /* IN/OUT: Right-hand buffer pointer */
  int *pnVal                      /* OUT: Bytes in returned value */
){
  u8 *a1 = *paOne;
  u8 *a2 = *paTwo;
  u8 *pRet = 0;
  int n1;

  assert( a1 );
................................................................................
    pRet = a1;
  }
  *paOne = &a1[n1];

  return pRet;
}

/*
** This function is used by changeset_concat() to merge two UPDATE changes
** on the same row.
*/
static int sessionMergeUpdate(

  u8 **paOut,                     /* IN/OUT: Pointer to output buffer */
  SessionTable *pTab,             /* Table change pertains to */
  u8 *aOldRecord1,                /* old.* record for first change */
  u8 *aOldRecord2,                /* old.* record for second change */
  u8 *aNewRecord1,                /* new.* record for first change */
  u8 *aNewRecord2                 /* new.* record for second change */
){
  u8 *aOld1 = aOldRecord1;
  u8 *aOld2 = aOldRecord2;
  u8 *aNew1 = aNewRecord1;
  u8 *aNew2 = aNewRecord2;

  u8 *aOut = *paOut;
................................................................................
){
  int i;
  u8 *a = pChange->aRecord;

  *pbEqual = 0;

  for(i=0; i<pTab->nCol; i++){

    if( !pTab->abPK[i] ){









      a += sessionSerialLen(a);




    }else{
      sqlite3_value *pVal;        /* Value returned by preupdate_new/old */
      int rc;                     /* Error code from preupdate_new/old */
      int eType = *a++;           /* Type of value from change record */

      /* The following calls to preupdate_new() and preupdate_old() can not
      ** fail. This is because they cache their return values, and by the
      ** time control flows to here they have already been called once from
      ** within sessionPreupdateHash(). The first two asserts below verify
      ** this (that the method has already been called). */
      if( bNew ){
................................................................................
      }

      /* Add the change to the hash-table */
      if( pSession->bIndirect || sqlite3_preupdate_depth(pSession->db) ){
        pChange->bIndirect = 1;
      }
      pChange->nRecord = nByte;
      pChange->op = op;
      pChange->pNext = pTab->apChange[iHash];
      pTab->apChange[iHash] = pChange;

    }else if( pC->bIndirect ){
      /* If the existing change is considered "indirect", but this current
      ** change is "direct", mark the change object as direct. */
      if( sqlite3_preupdate_depth(pSession->db)==0 && pSession->bIndirect==0 ){
................................................................................
      for(i=0; i<pTab->nChange && rc==SQLITE_OK; i++){
        SessionChange *p;         /* Used to iterate through changes */

        for(p=pTab->apChange[i]; rc==SQLITE_OK && p; p=p->pNext){
          rc = sessionSelectBind(pSel, nCol, abPK, p);
          if( rc!=SQLITE_OK ) continue;
          if( sqlite3_step(pSel)==SQLITE_ROW ){
            if( p->op==SQLITE_INSERT ){
              int iCol;

              sessionAppendByte(&buf, SQLITE_INSERT, &rc);
              sessionAppendByte(&buf, p->bIndirect, &rc);
              for(iCol=0; iCol<nCol; iCol++){
                sessionAppendCol(&buf, pSel, iCol, &rc);
              }
            }else{
              rc = sessionAppendUpdate(&buf, pSel, p, abPK);
            }
          }else if( p->op!=SQLITE_INSERT ){
            /* A DELETE change */
            sessionAppendByte(&buf, SQLITE_DELETE, &rc);
            sessionAppendByte(&buf, p->bIndirect, &rc);
            sessionAppendBlob(&buf, p->aRecord, p->nRecord, &rc);
          }
          if( rc==SQLITE_OK ){
            rc = sqlite3_reset(pSel);
................................................................................

  if( !pExist ){
    pNew = (SessionChange *)sqlite3_malloc(sizeof(SessionChange));
    if( !pNew ){
      return SQLITE_NOMEM;
    }
    memset(pNew, 0, sizeof(SessionChange));
    pNew->op = op2;
    pNew->bIndirect = bIndirect;
    pNew->nRecord = nRec;
    pNew->aRecord = aRec;
  }else{
    int op1 = pExist->op;

    /* 
    **   op1=INSERT, op2=INSERT      ->      Unsupported. Discard op2.
    **   op1=INSERT, op2=UPDATE      ->      INSERT.
    **   op1=INSERT, op2=DELETE      ->      (none)
    **
    **   op1=UPDATE, op2=INSERT      ->      Unsupported. Discard op2.
................................................................................
      memset(pNew, 0, sizeof(SessionChange));
      pNew->bIndirect = (bIndirect && pExist->bIndirect);
      aCsr = pNew->aRecord = (u8 *)&pNew[1];

      if( op1==SQLITE_INSERT ){             /* INSERT + UPDATE */
        u8 *a1 = aRec;
        assert( op2==SQLITE_UPDATE );
        pNew->op = SQLITE_INSERT;
        sessionReadRecord(&a1, pTab->nCol, 0);
        sessionMergeRecord(&aCsr, pTab->nCol, pExist->aRecord, a1);
      }else if( op1==SQLITE_DELETE ){       /* DELETE + INSERT */
        assert( op2==SQLITE_INSERT );
        pNew->op = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, pExist->aRecord, 0, aRec, 0) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else if( op2==SQLITE_UPDATE ){       /* UPDATE + UPDATE */
        assert( op1==SQLITE_UPDATE );
        u8 *a1 = pExist->aRecord;
        u8 *a2 = aRec;
        sessionReadRecord(&a1, pTab->nCol, 0);
        sessionReadRecord(&a2, pTab->nCol, 0);
        pNew->op = SQLITE_UPDATE;
        if( 0==sessionMergeUpdate(&aCsr, pTab, aRec, pExist->aRecord, a1, a2) ){
          sqlite3_free(pNew);
          pNew = 0;
        }
      }else{                                /* UPDATE + DELETE */
        assert( op1==SQLITE_UPDATE && op2==SQLITE_DELETE );
        pNew->op = SQLITE_DELETE;
        sessionMergeRecord(&aCsr, pTab->nCol, aRec, pExist->aRecord);
      }

      if( pNew ){
        pNew->nRecord = (aCsr - pNew->aRecord);
      }
      sqlite3_free(pExist);
    }
................................................................................
      int i;
      if( pTab->nEntry==0 ) continue;

      sessionAppendTableHdr(&buf, pTab, &rc);
      for(i=0; i<pTab->nChange; i++){
        SessionChange *p;
        for(p=pTab->apChange[i]; p; p=p->pNext){
          sessionAppendByte(&buf, p->op, &rc);
          sessionAppendByte(&buf, p->bIndirect, &rc);
          sessionAppendBlob(&buf, p->aRecord, p->nRecord, &rc);
        }
      }
    }

    if( rc==SQLITE_OK ){