Result set merge source code analysis
Find this method, the method that executes the query
com.dangdang.ddframe.rdb.sharding.jdbc.core.statement.ShardingPreparedStatement#executeQuery
@Override
public ResultSet executeQuery() throws SQLException {
ResultSet result;
try {
// route to the precompiled object execution unit collection
Collection<PreparedStatementUnit> preparedStatementUnits = route();
// Multi-threaded execution of sql query returns a collection of result set objects
List<ResultSet> resultSets = new PreparedStatementExecutor(
getShardingConnection().getShardingContext().getExecutorEngine(), getRouteResult().getSqlStatement().getType(), preparedStatementUnits, getParameters()).executeQuery();
//Go to the result count merge engine to execute the result set merge logic-"
result = new ShardingResultSet(resultSets, new MergeEngine(
getShardingConnection().getShardingContext().getDatabaseType(), resultSets, (SelectStatement) getRouteResult().getSqlStatement()).merge());
} finally {
clearBatch ();
}
setCurrentResultSet(result);
return result;
}
Create a result set merge engine object and enter the constructor
/**
* Sharded result set merge engine.
*
* @author zhangliang
*/
public final class MergeEngine {
private final DatabaseType databaseType;
private final List<ResultSet> resultSets;
private final SelectStatement selectStatement;
private final Map<String, Integer> columnLabelIndexMap;
public MergeEngine(final DatabaseType databaseType, final List<ResultSet> resultSets, final SelectStatement selectStatement) throws SQLException {
this.databaseType = databaseType;
this.resultSets = resultSets;
this.selectStatement = selectStatement;
columnLabelIndexMap = getColumnLabelIndexMap(resultSets.get(0));
}
Get the source data of the result set
columnLabelIndexMap = getColumnLabelIndexMap(resultSets.get(0));
private Map<String, Integer> getColumnLabelIndexMap(final ResultSet resultSet) throws SQLException {
// Get the source data of resultSet
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
Map<String, Integer> result = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
for (int i = 1; i <= resultSetMetaData.getColumnCount(); i++) {
result.put(SQLUtil.getExactlyValue(resultSetMetaData.getColumnLabel(i)), i);
}
return result;
}
into this method
com.dangdang.ddframe.rdb.sharding.merger.MergeEngine#merge
/**
* Merge result sets.
*
* @return merged result set
* @throws SQLException SQL异常
*/
public ResultSetMerger merge() throws SQLException {//Result set merge business method
selectStatement.setIndexForItems(columnLabelIndexMap);
return decorate(build());
}
into this method
com.dangdang.ddframe.rdb.sharding.merger.MergeEngine#build
private ResultSetMerger build() throws SQLException {
// The sort item is not empty or the aggregate selection is not empty
if (!selectStatement.getGroupByItems().isEmpty() || !selectStatement.getAggregationSelectItems().isEmpty()) {
// If the grouping item is the same as the sorting item, merge the result set in the stream-"
if (selectStatement.isSameGroupByAndOrderByItems()) {
return new GroupByStreamResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
} else {
// Otherwise, merge the result set in memory, try to avoid this situation, it will take up a lot of memory = "
return new GroupByMemoryResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
}
}
if (!selectStatement.getOrderByItems().isEmpty()) {
return new OrderByStreamResultSetMerger(resultSets, selectStatement.getOrderByItems(), getNullOrderType());
}
return new IteratorStreamResultSetMerger(resultSets);
}
return new GroupByStreamResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
Create a grouped streaming result set merge and enter the constructor method
public GroupByStreamResultSetMerger(
final Map<String, Integer> labelAndIndexMap, final List<ResultSet> resultSets, final SelectStatement selectStatement, final OrderType nullOrderType) throws SQLException {
super(resultSets, selectStatement.getOrderByItems(), nullOrderType);
this.labelAndIndexMap = labelAndIndexMap;
this.selectStatement = selectStatement;
currentRow = new ArrayList<>(labelAndIndexMap.size());
currentGroupByValues = getOrderByValuesQueue().isEmpty() ? Collections.emptyList() : new GroupByValue(getCurrentResultSet(), selectStatement.getGroupByItems()).getGroupValues();
}
this line of code
super(resultSets, selectStatement.getOrderByItems(), nullOrderType);
Create a sorted streaming result set merge object
public OrderByStreamResultSetMerger(final List<ResultSet> resultSets, final List<OrderItem> orderByItems, final OrderType nullOrderType) throws SQLException {
this.orderByItems = orderByItems;
// Priority queue implementation
this.orderByValuesQueue = new PriorityQueue<>(resultSets.size());
this.nullOrderType = nullOrderType;
// Put the result set to be sorted into the queue-"
orderResultSetsToQueue (resultSets);
isFirstNext = true;
}
// Put the result set to be sorted into the queue-" orderResultSetsToQueue (resultSets);
private void orderResultSetsToQueue(final List<ResultSet> resultSets) throws SQLException {
for (ResultSet each : resultSets) {
OrderByValue orderByValue = new OrderByValue (each, orderByItems, nullOrderType);
if (orderByValue.next()) {
orderByValuesQueue.offer(orderByValue);
}
}
// Stream result set merge, set the current stream merge result set, everyone sees that the current result set is stored here, so there will be no memory overflow problem
setCurrentResultSet(orderByValuesQueue.isEmpty() ? resultSets.get(0) : orderByValuesQueue.peek().getResultSet());
}
return to this method
private ResultSetMerger build() throws SQLException {
// The sort item is not empty or the aggregate selection is not empty
if (!selectStatement.getGroupByItems().isEmpty() || !selectStatement.getAggregationSelectItems().isEmpty()) {
// If the grouping item is the same as the sorting item, merge the result set in the stream-"
if (selectStatement.isSameGroupByAndOrderByItems()) {
return new GroupByStreamResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
} else {
// Otherwise, merge the result set in memory, try to avoid this situation, it will take up a lot of memory = "
return new GroupByMemoryResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
}
}
if (!selectStatement.getOrderByItems().isEmpty()) {
return new OrderByStreamResultSetMerger(resultSets, selectStatement.getOrderByItems(), getNullOrderType());
}
return new IteratorStreamResultSetMerger(resultSets);
}
this line
// Otherwise, merge the result set in memory, try to avoid this situation, it will take up a lot of memory = " return new GroupByMemoryResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
Create an in-memory grouped result set merge object
public GroupByMemoryResultSetMerger(
final Map<String, Integer> labelAndIndexMap, final List<ResultSet> resultSets, final SelectStatement selectStatement, final OrderType nullOrderType) throws SQLException {
super(labelAndIndexMap);
this.selectStatement = selectStatement;
this.nullOrderType = nullOrderType;
// Create an in-memory result set row object
memoryResultSetRows = init(resultSets);
}
return to this method
private ResultSetMerger build() throws SQLException {
// The sort item is not empty or the aggregate selection is not empty
if (!selectStatement.getGroupByItems().isEmpty() || !selectStatement.getAggregationSelectItems().isEmpty()) {
// If the grouping item is the same as the sorting item, merge the result set in the stream-"
if (selectStatement.isSameGroupByAndOrderByItems()) {
return new GroupByStreamResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
} else {
// Otherwise, merge the result set in memory, try to avoid this situation, it will take up a lot of memory = "
return new GroupByMemoryResultSetMerger(columnLabelIndexMap, resultSets, selectStatement, getNullOrderType());
}
}
if (!selectStatement.getOrderByItems().isEmpty()) {
return new OrderByStreamResultSetMerger(resultSets, selectStatement.getOrderByItems(), getNullOrderType());
}
// Create an iterative merge result set merge object
return new IteratorStreamResultSetMerger(resultSets);
}
this line
// Create an iterative merge result set merge object return new IteratorStreamResultSetMerger(resultSets);
public IteratorStreamResultSetMerger(final List<ResultSet> resultSets) {
this.resultSets = resultSets.iterator();
setCurrentResultSet(this.resultSets.next());
}
return to this method
/**
* Merge result sets.
*
* @return merged result set
* @throws SQLException SQL异常
*/
public ResultSetMerger merge() throws SQLException {//Result set merge business method
selectStatement.setIndexForItems(columnLabelIndexMap);
return decorate(build());
}
Enter this method com.dangdang.ddframe.rdb.sharding.merger.MergeEngine#decorate
private ResultSetMerger decorate(final ResultSetMerger resultSetMerger) throws SQLException {
ResultSetMerger result = resultSetMerger;
if (null != selectStatement.getLimit()) {
// The decorator pattern further encapsulates the paging result set merging
result = new LimitDecoratorResultSetMerger(result, selectStatement.getLimit());
}
return result;
}
The result set merge source code parsing ends here.
to the end
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