drcrallen 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_r202750042
##########
File path: server/src/main/java/io/druid/client/CachingClusteredClient.java
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@@ -471,94 +552,162 @@ private CachePopulator getCachePopulator(String
segmentId, Interval segmentInter
return cachePopulatorMap.get(StringUtils.format("%s_%s", segmentId,
segmentInterval));
}
- private SortedMap<DruidServer, List<SegmentDescriptor>>
groupSegmentsByServer(Set<ServerToSegment> segments)
+ /**
+ * Check the input stream to see what was cached and what was not. For the
ones that were cached, merge the results
+ * and return the merged sequence. For the ones that were NOT cached, get
the server result sequence queued up into
+ * the stream response
+ *
+ * @param segmentOrResult A list that is traversed in order to determine
what should be sent back. All segments
+ * should be on the same server.
+ *
+ * @return A sequence of either the merged cached results, or the server
results from any particular server
+ */
+ private Sequence<T> runOnServer(List<ServerMaybeSegmentMaybeCache<T>>
segmentOrResult)
{
- final SortedMap<DruidServer, List<SegmentDescriptor>> serverSegments =
Maps.newTreeMap();
- for (ServerToSegment serverToSegment : segments) {
- final QueryableDruidServer queryableDruidServer =
serverToSegment.getServer().pick();
-
- if (queryableDruidServer == null) {
- log.makeAlert(
- "No servers found for SegmentDescriptor[%s] for DataSource[%s]?!
How can this be?!",
- serverToSegment.getSegmentDescriptor(),
- query.getDataSource()
- ).emit();
- } else {
- final DruidServer server = queryableDruidServer.getServer();
- serverSegments.computeIfAbsent(server, s -> new
ArrayList<>()).add(serverToSegment.getSegmentDescriptor());
- }
+ final List<SegmentDescriptor> segmentsOfServer = segmentOrResult.stream(
+ ).map(
+ ServerMaybeSegmentMaybeCache::getSegmentDescriptor
+ ).filter(
+ Optional::isPresent
+ ).map(
+ Optional::get
+ ).collect(
+ Collectors.toList()
+ );
+
+ // We should only ever have cache or queries to run, not both. So if we
have no segments, try caches
+ if (segmentsOfServer.isEmpty()) {
+ // Have a special sequence for the cache results so the merge doesn't
go all crazy.
+ // See
io.druid.java.util.common.guava.MergeSequenceTest.testScrewsUpOnOutOfOrder for
an example
+ // With zero results actually being found (no segments no caches) this
should essentially return a no-op
+ // merge sequence
+ return new MergeSequence<>(query.getResultOrdering(), Sequences.simple(
+ segmentOrResult.stream(
+ ).map(
+ ServerMaybeSegmentMaybeCache::getCachedValue
+ ).filter(
+ Optional::isPresent
+ ).map(
+ Optional::get
Review comment:
more recent versions of java have better Optional and Stream support
together, but java8 is missing some of that functionality. I'd rather leave it
as is for clarity of what it is doing unless there's a specific gain to be had
by adding in null handling in the pipeline over Optionals
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