SQLite

  ** nMinMerge.
  **
  ** Of course, updating the input segments also involves deleting a bunch
  ** of blocks from the segments table. But this is not considered overhead
  ** as it would also be required by a crisis-merge that used the same input 
  ** segments.
  */
  const u32 nMinMerge = 64;       /* Minimum amount of incr-merge work to do */

  Fts3Table *p = (Fts3Table*)pVtab;
  int rc = sqlite3Fts3PendingTermsFlush(p);

  if( rc==SQLITE_OK && p->bAutoincrmerge==1 && p->nLeafAdd>(nMinMerge/16) ){
    int mxLevel = 0;              /* Maximum relative level value in db */
    int A;                        /* Incr-merge parameter A */

    rc = sqlite3Fts3MaxLevel(p, &mxLevel);
    assert( rc==SQLITE_OK || mxLevel==0 );
    A = p->nLeafAdd * mxLevel;
    A += (A/2);
    if( A>(int)nMinMerge ) rc = sqlite3Fts3Incrmerge(p, A, 8);
  }
  sqlite3Fts3SegmentsClose(p);
  return rc;
}

/*
** Implementation of xBegin() method. This is a no-op.

    if( rc==SQLITE_OK && bAppendable ){
      /* It is possible to append to this segment. Set up the IncrmergeWriter
      ** object to do so.  */
      int i;
      int nHeight = (int)aRoot[0];
      NodeWriter *pNode;

      pWriter->nLeafEst = (int)((iEnd - iStart) + 1)/FTS_MAX_APPENDABLE_HEIGHT;
      pWriter->iStart = iStart;
      pWriter->iEnd = iEnd;
      pWriter->iAbsLevel = iAbsLevel;
      pWriter->iIdx = iIdx;

      for(i=nHeight+1; i<FTS_MAX_APPENDABLE_HEIGHT; i++){
        pWriter->aNodeWriter[i].iBlock = pWriter->iStart + i*pWriter->nLeafEst;
      }

      pNode = &pWriter->aNodeWriter[nHeight];
      pNode->iBlock = pWriter->iStart + pWriter->nLeafEst*nHeight;
      blobGrowBuffer(&pNode->block, MAX(nRoot, p->nNodeSize), &rc);
      if( rc==SQLITE_OK ){
        memcpy(pNode->block.a, aRoot, nRoot);
        pNode->block.n = nRoot;
      }

      for(i=nHeight; i>=0 && rc==SQLITE_OK; i--){

        NodeReader reader;
        pNode = &pWriter->aNodeWriter[i];

        rc = nodeReaderInit(&reader, pNode->block.a, pNode->block.n);
        while( reader.aNode && rc==SQLITE_OK ) rc = nodeReaderNext(&reader);
        blobGrowBuffer(&pNode->key, reader.term.n, &rc);
        if( rc==SQLITE_OK ){
          memcpy(pNode->key.a, reader.term.a, reader.term.n);
          pNode->key.n = reader.term.n;

  sqlite3_int64 iAbsLevel,        /* Absolute level of input segments */
  int iIdx,                       /* Index of new output segment */
  Fts3MultiSegReader *pCsr,       /* Cursor that data will be read from */
  IncrmergeWriter *pWriter        /* Populate this object */
){
  int rc;                         /* Return Code */
  int i;                          /* Iterator variable */
  int nLeafEst = 0;               /* Blocks allocated for leaf nodes */
  sqlite3_stmt *pLeafEst = 0;     /* SQL used to determine nLeafEst */
  sqlite3_stmt *pFirstBlock = 0;  /* SQL used to determine first block */

  /* Calculate nLeafEst. */
  rc = fts3SqlStmt(p, SQL_MAX_LEAF_NODE_ESTIMATE, &pLeafEst, 0);
  if( rc==SQLITE_OK ){
    sqlite3_bind_int64(pLeafEst, 1, iAbsLevel);

            }else{
              pCsr += sqlite3Fts3GetVarint(pCsr, &iVal);
              iDocid += iVal;
            }
          }else{
            iPos += (iVal - 2);
            cksum = cksum ^ fts3ChecksumEntry(
                csr.zTerm, csr.nTerm, iLangid, iIndex, iDocid,
                (int)iCol, (int)iPos
            );
          }
        }
      }
    }
  }
  sqlite3Fts3SegReaderFinish(&csr);

        /* For length() and typeof() functions with a column argument,
        ** set the P5 parameter to the OP_Column opcode to OPFLAG_LENGTHARG
        ** or OPFLAG_TYPEOFARG respectively, to avoid unnecessary data
        ** loading.
        */
        if( (pDef->flags & (SQLITE_FUNC_LENGTH|SQLITE_FUNC_TYPEOF))!=0 ){
          u8 exprOp;
          assert( nFarg==1 );
          assert( pFarg->a[0].pExpr!=0 );
          exprOp = pFarg->a[0].pExpr->op;
          if( exprOp==TK_COLUMN || exprOp==TK_AGG_COLUMN ){
            assert( SQLITE_FUNC_LENGTH==OPFLAG_LENGTHARG );
            assert( SQLITE_FUNC_TYPEOF==OPFLAG_TYPEOFARG );
            testcase( pDef->flags==SQLITE_FUNC_LENGTH );
            pFarg->a[0].pExpr->op2 = pDef->flags;
          }
        }