Method TableStats

src/java/simpledb/optimizer/TableStats.java:98–168

Create a new TableStats object, that keeps track of statistics on each column of a table @param tableid The table over which to compute statistics @param ioCostPerPage The cost per page of IO. This doesn't differentiate between sequential-scan IO and disk seeks.

(int tableid, int ioCostPerPage)

     *            sequential-scan IO and disk seeks.
     */
    public TableStats(int tableid, int ioCostPerPage) {
        // For this function, you'll have to get the
        // DbFile for the table in question,
        // then scan through its tuples and calculate
        // the values that you need.
        // You should try to do this reasonably efficiently, but you don't
        // necessarily have to (for example) do everything
        // in a single scan of the table.
        // some code goes here
        this.tableId = tableid;
        this.ioCostPerPage = ioCostPerPage;
        HeapFile heapFile = (HeapFile) catalog.getDatabaseFile(tableid);
        this.tupleDesc  = heapFile.getTupleDesc();
        this.numPages = heapFile.numPages();
        this.dbFileIterator = heapFile.iterator(new TransactionId());

        this.max  = new int[tupleDesc.numFields()];
        this.min = new int[tupleDesc.numFields()];
        this.intHistograms = new IntHistogram[tupleDesc.numFields()];
        Arrays.fill(min,Integer.MAX_VALUE);
        Arrays.fill(max,Integer.MIN_VALUE);

        try {
            this.dbFileIterator.open();
            while(dbFileIterator.hasNext()){
                this.total++;
                Tuple tuple = dbFileIterator.next();
                for(int i=0;i<max.length;i++){
                    Type fieldType = tuple.getField(i).getType();
                    if(fieldType.equals(Type.INT_TYPE)){
                        IntField field = (IntField)tuple.getField(i);
                        int value = field.getValue();
                        if(value>max[i]){
                            max[i] = value;
                        }
                        if(value<min[i]){
                            min[i]  =value;
                        }
                    }
                }
            }
        } catch (DbException e) {
            e.printStackTrace();
        } catch (TransactionAbortedException e) {
            e.printStackTrace();
        }


        for(int i=0;i<tupleDesc.numFields();i++){
            Type fieldType = tupleDesc.getFieldType(i);
            if(fieldType.equals(Type.STRING_TYPE)){
                continue;
            }
            this.intHistograms[i]  =new IntHistogram(100,min[i],max[i]);
            try {
                this.dbFileIterator.rewind();
                while(dbFileIterator.hasNext()){
                    Tuple tuple = dbFileIterator.next();