exercise 1
实现Filter和Join的操作，对应sql的where和join语法，所有的Operator都需要遍历，因此都需要实现迭代器逻辑，可以参考Project和OrderBy 字段类型，实验1需要实现
- src/java/simpledb/execution/Predicate.java
- src/java/simpledb/execution/JoinPredicate.java
- src/java/simpledb/execution/Filter.java
- src/java/simpledb/execution/Join.java
同时需要通过PredicateTest，JoinPredicateTest，FilterTest，JoinTest
exercise 2
实现几个分组聚合的函数，比如sum, count, avg, min, max，大概的思路是定义map用来存分组field和聚合值的下标，下标为聚合值的list下标，需要注意的是 在求avg的时候需要知道当前组的元素个数，因此还需要用一个map存储。IntegerAggregator和StringAggregator是基本字段的聚合器，外部使用通过Aggregate 获取聚合结果。
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class Main {
public void mergeTupleIntoGroup(Tuple tup) {
Field groupByField;
Field aggregateField = tup.getField(aggregateFieldIndex);
if (groupByFieldIndex == NO_GROUPING) {
groupByField = new IntField(Integer.MAX_VALUE);
} else {
groupByField = tup.getField(groupByFieldIndex);
}
Integer index = fieldWithTupleIndex.get(groupByField);
if (index == null) {
Tuple tuple = new Tuple(tupleDesc);
tuple.setField(0, groupByField);
tuple.setField(1, aggregateField);
fieldWithTupleIndex.put(groupByField, aggregateTuples.size());
aggregateTuples.add(tuple);
} else {
Tuple tuple = aggregateTuples.get(index);
int aggregateFieldValue = ((IntField) aggregateField).getValue();
int tupleFieldValue = ((IntField) tuple.getField(1)).getValue();
switch (op) {
case SUM: {
tuple.setField(1, new IntField(aggregateFieldValue + tupleFieldValue));
break;
}
case MIN: {
tuple.setField(1, new IntField(Math.min(aggregateFieldValue, tupleFieldValue)));
break;
}
case MAX: {
tuple.setField(1, new IntField(Math.max(aggregateFieldValue, tupleFieldValue)));
break;
}
case AVG: {
tuple.setField(1, new IntField((aggregateFieldValue + tupleFieldValue) / 2));
break;
}
}
}
}
}
实验2需要实现
- src/java/simpledb/execution/IntegerAggregator.java
- src/java/simpledb/execution/StringAggregator.java
- src/java/simpledb/execution/Aggregate.java
并通过IntegerAggregatorTest，StringAggregatorTest，AggregateTest
exercise 3
实现HeapFile和HeapPage的insert和delete，HeapFile和HeapPage中都有，HeapFile重点在找到能插入的HeapPage，然后调用HeapPage的方法就行，重点逻辑在HeapPage 插入：记录当前页最后插入位置，往数组里设置tuple，同时更新header 删除：通过recordId删除指定位置的tuple，同时更新header 最后再实现BufferPool里的insert和delete方法 实验3需要实现
- src/java/simpledb/storage/HeapPage.java
- src/java/simpledb/storage/HeapFile.java
- src/java/simpledb/storage/BufferPool.java
并通过HeapPageWriteTest，HeapFileWriteTest的addTuple，BufferPoolWriteTest
exercise 4
实现Insert和Delete类，作为insert和delete的SQL语句具体执行类，底层还是调用的实验3写的insertTuple和deleteTuple，这里需要实现writePage方法， 在insert或者delete之后调用，把操作结果落盘 实现2需要实现
- src/java/simpledb/execution/Insert.java
- src/java/simpledb/execution/Delete.java
并通过InsertTest, DeleteTest, HeapFileWriteTest，HeapPageWriteTest，systemtest/InsertTest，systemtest/DeleteTest
exercise 5
实现页置换算法，当BufferPool的pages满了后，需要挑选一页置换，可以选择LRU，LFU，Clock等 实验5需要实现
- src/java/simpledb/storage/BufferPool.java
并通过systemtest/EvictionTest
