jihoonson commented on a change in pull request #5913: Move Caching Cluster
Client to java streams and allow parallel intermediate merges
URL: https://github.com/apache/incubator-druid/pull/5913#discussion_r213499301
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File path: server/src/main/java/io/druid/client/CachingClusteredClient.java
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@@ -242,74 +305,93 @@ public CachingClusteredClient(
contextBuilder.put(CacheConfig.POPULATE_CACHE, false);
contextBuilder.put("bySegment", true);
}
- return contextBuilder.build();
+ return Collections.unmodifiableMap(contextBuilder);
}
- Sequence<T> run(final UnaryOperator<TimelineLookup<String,
ServerSelector>> timelineConverter)
+ Stream<Sequence<T>> run(final UnaryOperator<TimelineLookup<String,
ServerSelector>> timelineConverter)
{
@Nullable
TimelineLookup<String, ServerSelector> timeline =
serverView.getTimeline(query.getDataSource());
if (timeline == null) {
- return Sequences.empty();
+ return Stream.empty();
}
timeline = timelineConverter.apply(timeline);
if (uncoveredIntervalsLimit > 0) {
computeUncoveredIntervals(timeline);
}
- final Set<ServerToSegment> segments = computeSegmentsToQuery(timeline);
+ Stream<ServerToSegment> segments = computeSegmentsToQuery(timeline);
@Nullable
final byte[] queryCacheKey = computeQueryCacheKey();
if (query.getContext().get(QueryResource.HEADER_IF_NONE_MATCH) != null) {
+ // Materialize then re-stream
+ final List<ServerToSegment> materializedSegments =
segments.collect(Collectors.toList());
+ segments = materializedSegments.stream();
+
@Nullable
final String prevEtag = (String)
query.getContext().get(QueryResource.HEADER_IF_NONE_MATCH);
@Nullable
- final String currentEtag = computeCurrentEtag(segments, queryCacheKey);
+ final String currentEtag = computeCurrentEtag(materializedSegments,
queryCacheKey);
if (currentEtag != null && currentEtag.equals(prevEtag)) {
- return Sequences.empty();
+ return Stream.empty();
}
}
- final List<Pair<Interval, byte[]>> alreadyCachedResults =
pruneSegmentsWithCachedResults(queryCacheKey, segments);
- final SortedMap<DruidServer, List<SegmentDescriptor>> segmentsByServer =
groupSegmentsByServer(segments);
- return new LazySequence<>(() -> {
- List<Sequence<T>> sequencesByInterval = new
ArrayList<>(alreadyCachedResults.size() + segmentsByServer.size());
- addSequencesFromCache(sequencesByInterval, alreadyCachedResults);
- addSequencesFromServer(sequencesByInterval, segmentsByServer);
- return Sequences
- .simple(sequencesByInterval)
- .flatMerge(seq -> seq, query.getResultOrdering());
- });
+ // This pipeline follows a few general steps:
+ // 1. Fetch cache results - Unfortunately this is an eager operation so
that the non cached items can
Review comment:
I wonder if the below is feasible.
1. Group the segment information by server
2. Per server, check the cache and fetch the results if they are cached.
3. Call `runOnServer()` on cache misses.
I would say the benefit of this is we probably do everything lazily until
the query results are fetched either from the cache or servers.
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