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_r202752792
##########
File path: server/src/main/java/io/druid/client/CachingClusteredClient.java
##########
@@ -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
+ ).map(
+ Collections::singletonList
+ ).map(
+ Sequences::simple
+ )
+ ));
}
- return serverSegments;
- }
- private void addSequencesFromCache(
- final List<Sequence<T>> listOfSequences,
- final List<Pair<Interval, byte[]>> cachedResults
- )
- {
- if (strategy == null) {
- return;
+ final DruidServer server = segmentOrResult.get(0).getServer();
+ final QueryRunner serverRunner = serverView.getQueryRunner(server);
+
+ if (serverRunner == null) {
+ log.error("Server[%s] doesn't have a query runner", server);
+ return Sequences.empty();
}
- final Function<Object, T> pullFromCacheFunction =
strategy.pullFromSegmentLevelCache();
- final TypeReference<Object> cacheObjectClazz =
strategy.getCacheObjectClazz();
- for (Pair<Interval, byte[]> cachedResultPair : cachedResults) {
- final byte[] cachedResult = cachedResultPair.rhs;
- Sequence<Object> cachedSequence = new BaseSequence<>(
- new BaseSequence.IteratorMaker<Object, Iterator<Object>>()
- {
- @Override
- public Iterator<Object> make()
- {
- try {
- if (cachedResult.length == 0) {
- return Collections.emptyIterator();
- }
+ final MultipleSpecificSegmentSpec segmentsOfServerSpec = new
MultipleSpecificSegmentSpec(segmentsOfServer);
- return objectMapper.readValues(
- objectMapper.getFactory().createParser(cachedResult),
- cacheObjectClazz
- );
- }
- catch (IOException e) {
- throw new RuntimeException(e);
- }
- }
+ final Sequence<T> serverResults;
+ if (isBySegment) {
+ serverResults = getBySegmentServerResults(serverRunner,
segmentsOfServerSpec);
+ } else if (!server.segmentReplicatable() || !populateCache) {
+ serverResults = getSimpleServerResults(serverRunner,
segmentsOfServerSpec);
+ } else {
+ serverResults = getAndCacheServerResults(serverRunner,
segmentsOfServerSpec);
+ }
+ return serverResults;
+ }
- @Override
- public void cleanup(Iterator<Object> iterFromMake)
- {
- }
- }
+ private ServerMaybeSegmentMaybeCache<T>
pickServer(SerializablePair<ServerToSegment, Optional<T>> tuple)
+ {
+ final Optional<T> maybeResult = tuple.getRhs();
+ if (maybeResult.isPresent()) {
+ return new ServerMaybeSegmentMaybeCache<T>(ALREADY_CACHED_SERVER,
Optional.empty(), maybeResult);
+ }
+ final ServerToSegment serverToSegment = tuple.getLhs();
+ 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();
+ return new ServerMaybeSegmentMaybeCache<T>(
+ ALREADY_CACHED_SERVER,
+ Optional.empty(),
+ Optional.empty()
);
- listOfSequences.add(Sequences.map(cachedSequence,
pullFromCacheFunction));
}
+ final DruidServer server = queryableDruidServer.getServer();
+ return new ServerMaybeSegmentMaybeCache<T>(
+ server,
+ Optional.ofNullable(serverToSegment.getSegmentDescriptor()),
+ Optional.empty()
+ );
}
- private void addSequencesFromServer(
- final List<Sequence<T>> listOfSequences,
- final SortedMap<DruidServer, List<SegmentDescriptor>> segmentsByServer
- )
+ // This materializes the input stream in order to group it by server
+ // This method takes in the stream of cache resolved items and will group
all the items by server.
+ // Each entry in the output stream contains a list whose entries'
getServer is the same
+ // Each entry will either have a present segemnt descriptor or a present
result, but not both
+ // Downstream consumers should check each and handle appropriately.
+ private Stream<List<ServerMaybeSegmentMaybeCache<T>>>
groupCachedResultsByServer(Stream<SerializablePair<ServerToSegment,
Optional<T>>> cacheResolvedStream)
{
- segmentsByServer.forEach((server, segmentsOfServer) -> {
- final QueryRunner serverRunner = serverView.getQueryRunner(server);
+ return cacheResolvedStream.map(
+ this::pickServer
+ ).collect(
+ Collectors.groupingBy(ServerMaybeSegmentMaybeCache::getServer)
+ ).values(
+ // Even though we have matrialized the map, and are iterating across
the values,
+ // the java.util.HashMap.ValueSpliterator does not currently support
things like sizing or subsetting,
+ // so we want to convert the collection into a form conducive with
embarassing parallelization down the line
Review comment:
My understanding of the use of Spliterators is to handle just this kind of
scenario, where you can split / apply / combine work. As such, this PR includes
ways to use such mechanisms in a standard java way whenever possible.
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