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_r202753768
##########
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:
this code got refactored into `deserializeFromCache` for the materialization
components it looks like, but the comment didn't move.
The comment is still valid though, we have a fixed size map resulting out,
but the standard java stream implementation doesn't yet have a "fixed map value
spliterator" optimization. There is no reason to believe it wouldn't in the
future though. Or that a "fixed result size grouping collector" would be
unfeasible. Such optimizations or framework improvements are beyond the scope
of this PR. It is better to just document the current behavior and the points
where that behavior influences parts of the code base.
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