Question

我的问题涉及Cassandra 0.8和Pelops。我发现Pelops使用相同的Thrift命令来读取一片列，就像一片计数器列一样。然后，它遍历检索到的Thrift ColumnOrSuperColumn对象的集合，声明该列（或counter_column）字段不为null。似乎很明显，对于混合列族，执行这些方法中的任何一个都会失败。

那么，Cassandra是否要求列族中的所有列都属于同一类型？

以下代码是Pelops的Selector类的片段。

private List<Column> getColumnsFromRow(final ColumnParent colParent, final Bytes rowKey, final SlicePredicate colPredicate, final ConsistencyLevel cLevel) throws PelopsException {
    IOperation<List<Column>> operation = new IOperation<List<Column>>() {
        @Override
        public List<Column> execute(IPooledConnection conn) throws Exception {
            List<ColumnOrSuperColumn> apiResult = conn.getAPI().get_slice(safeGetRowKey(rowKey), colParent, colPredicate, cLevel);
            return toColumnList(apiResult);
        }
    };
    return tryOperation(operation);
}

private List<CounterColumn> getCounterColumnsFromRow(final ColumnParent colParent, final Bytes rowKey, final SlicePredicate colPredicate, final ConsistencyLevel cLevel) throws PelopsException {
    IOperation<List<CounterColumn>> operation = new IOperation<List<CounterColumn>>() {
        @Override
        public List<CounterColumn> execute(IPooledConnection conn) throws Exception {
            List<ColumnOrSuperColumn> apiResult = conn.getAPI().get_slice(safeGetRowKey(rowKey), colParent, colPredicate, cLevel);
            return toCounterColumnList(apiResult);
        }
    };
    return tryOperation(operation);
}

private static List<Column> toColumnList(List<ColumnOrSuperColumn> coscList) {
    List<Column> columns = new ArrayList<Column>(coscList.size());
    for (ColumnOrSuperColumn cosc : coscList) {
        assert cosc.column != null : "The column should not be null";
        columns.add(cosc.column);
    }
    return columns;
}

private static List<CounterColumn> toCounterColumnList(List<ColumnOrSuperColumn> coscList) {
    List<CounterColumn> columns = new ArrayList<CounterColumn>(coscList.size());
    for (ColumnOrSuperColumn cosc : coscList) {
        assert cosc.counter_column != null : "The column should not be null";
        columns.add(cosc.counter_column);
    }
    return columns;
}

Answer 1

那么，Cassandra是否需要全部列族中的列是属于同一类型？

是的，从某种意义上说，它确实要求CF包含所有计数器或所有非计数器。但是，

This will change，可能是0.8.1
非计数器肯定不必是相同的数据类型（bytes，long，utf8等都可以在同一行中混合）

我是否需要为计数器列创建一个特殊的列系列？

1 个答案: