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[GitHub] drcrallen commented on a change in pull request #5913: Move Caching Cluster Client to java streams and allow parallel intermediate merges


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_r202769403
 
 

 ##########
 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)
 
 Review comment:
   fixed

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