jon-wei commented on a change in pull request #7133: 6088 - Time Ordering On
Scans
URL: https://github.com/apache/incubator-druid/pull/7133#discussion_r267602505
##########
File path:
processing/src/main/java/org/apache/druid/query/scan/ScanQueryRunnerFactory.java
##########
@@ -68,34 +81,117 @@ public ScanQueryRunnerFactory(
)
{
// in single thread and in jetty thread instead of processing thread
- return new QueryRunner<ScanResultValue>()
- {
- @Override
- public Sequence<ScanResultValue> run(
- final QueryPlus<ScanResultValue> queryPlus, final Map<String,
Object> responseContext
- )
- {
- // Note: this variable is effective only when queryContext has a
timeout.
- // See the comment of CTX_TIMEOUT_AT.
- final long timeoutAt = System.currentTimeMillis() +
QueryContexts.getTimeout(queryPlus.getQuery());
- responseContext.put(CTX_TIMEOUT_AT, timeoutAt);
+ return (queryPlus, responseContext) -> {
+ ScanQuery query = (ScanQuery) queryPlus.getQuery();
+ int numSegments = 0;
+ final Iterator<QueryRunner<ScanResultValue>> segmentIt =
queryRunners.iterator();
+ for (; segmentIt.hasNext(); numSegments++) {
+ segmentIt.next();
+ }
+ // Note: this variable is effective only when queryContext has a timeout.
+ // See the comment of CTX_TIMEOUT_AT.
+ final long timeoutAt = System.currentTimeMillis() +
QueryContexts.getTimeout(queryPlus.getQuery());
+ responseContext.put(CTX_TIMEOUT_AT, timeoutAt);
+ if (query.getOrder().equals(ScanQuery.Order.NONE)) {
+ // Use normal strategy
return Sequences.concat(
Sequences.map(
Sequences.simple(queryRunners),
- new Function<QueryRunner<ScanResultValue>,
Sequence<ScanResultValue>>()
- {
- @Override
- public Sequence<ScanResultValue> apply(final
QueryRunner<ScanResultValue> input)
- {
- return input.run(queryPlus, responseContext);
- }
- }
+ input -> input.run(queryPlus, responseContext)
)
);
+ } else if (query.getLimit() <=
scanQueryConfig.getMaxRowsQueuedForTimeOrdering()) {
+ // Use priority queue strategy
+ return sortAndLimitScanResultValues(
+ Sequences.concat(Sequences.map(
+ Sequences.simple(queryRunners),
+ input -> input.run(queryPlus, responseContext)
+ )),
+ query
+ );
+ } else if (numSegments <=
scanQueryConfig.getMaxSegmentsTimeOrderedInMemory()) {
+ // Use n-way merge strategy
+ final Sequence<ScanResultValue> unbatched =
+ Sequences.map(
+ Sequences.simple(queryRunners),
+ (input) -> Sequences.concat(
+ Sequences.map(
+ input.run(queryPlus, responseContext),
+ srv ->
Sequences.simple(srv.toSingleEventScanResultValues())
+ )
+ )
+ ).flatMerge(
+ seq -> seq,
+ Ordering.from(new ScanResultValueTimestampComparator(
+ query
+ )).reverse() // This needs to be reversed because
+ ).limit(
+ Math.toIntExact(query.getLimit())
+ );
+
+ return unbatched;
}
+ throw new UOE(
+ "Time ordering for queries of %,d segments per historical and a row
limit of %,d is not supported."
+ + " Try reducing the scope of the query to scan fewer segments than
the configurable segment limit of"
+ + " %,d segments or lower the row limit below %,d.",
+ numSegments,
+ query.getLimit(),
+ scanQueryConfig.getMaxSegmentsTimeOrderedInMemory(),
+ scanQueryConfig.getMaxRowsQueuedForTimeOrdering()
+ );
};
}
+ @VisibleForTesting
+ Sequence<ScanResultValue> sortAndLimitScanResultValues(
+ Sequence<ScanResultValue> inputSequence,
+ ScanQuery scanQuery
+ )
+ {
+ Comparator<ScanResultValue> priorityQComparator = new
ScanResultValueTimestampComparator(scanQuery);
+
+ // Converting the limit from long to int could theoretically throw an
ArithmeticException but this branch
+ // only runs if limit < MAX_LIMIT_FOR_IN_MEMORY_TIME_ORDERING (which
should be < Integer.MAX_VALUE)
+ int limit = Math.toIntExact(scanQuery.getLimit());
+
+ PriorityQueue<ScanResultValue> q = new PriorityQueue<>(limit,
priorityQComparator);
+
+ Yielder<ScanResultValue> yielder = inputSequence.toYielder(
+ null,
+ new YieldingAccumulator<ScanResultValue, ScanResultValue>()
+ {
+ @Override
+ public ScanResultValue accumulate(ScanResultValue accumulated,
ScanResultValue in)
+ {
+ yield();
+ return in;
+ }
+ }
+ );
+ while (!yielder.isDone()) {
+ ScanResultValue next = yielder.get();
+ List<ScanResultValue> singleEventScanResultValues =
next.toSingleEventScanResultValues();
+ for (ScanResultValue srv : singleEventScanResultValues) {
Review comment:
I would make it conditional (maybe you have more than Int.MAX_VALUE rows?)
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