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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2020/06/28 12:04:18 UTC
[GitHub] [druid] clintropolis commented on a change in pull request #10082: Fix RetryQueryRunner to actually do the job
clintropolis commented on a change in pull request #10082:
URL: https://github.com/apache/druid/pull/10082#discussion_r446626252
##########
File path: server/src/main/java/org/apache/druid/query/RetryQueryRunner.java
##########
@@ -0,0 +1,250 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import org.apache.druid.java.util.common.ISE;
+import org.apache.druid.java.util.common.guava.BaseSequence;
+import org.apache.druid.java.util.common.guava.BaseSequence.IteratorMaker;
+import org.apache.druid.java.util.common.guava.MergeSequence;
+import org.apache.druid.java.util.common.guava.Sequence;
+import org.apache.druid.java.util.common.guava.Yielder;
+import org.apache.druid.java.util.common.guava.YieldingAccumulator;
+import org.apache.druid.java.util.common.guava.YieldingSequenceBase;
+import org.apache.druid.java.util.common.logger.Logger;
+import org.apache.druid.query.context.ResponseContext;
+import org.apache.druid.query.context.ResponseContext.Key;
+import org.apache.druid.segment.SegmentMissingException;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.BiFunction;
+
+public class RetryQueryRunner<T> implements QueryRunner<T>
+{
+ private static final Logger LOG = new Logger(RetryQueryRunner.class);
+
+ private final QueryRunner<T> baseRunner;
+ private final BiFunction<Query<T>, List<SegmentDescriptor>, QueryRunner<T>> retryRunnerCreateFn;
+ private final RetryQueryRunnerConfig config;
+ private final ObjectMapper jsonMapper;
+
+ /**
+ * Runnable executed after the broker creates query distribution tree for the first attempt. This is only
+ * for testing and must not be used in production code.
+ */
+ private final Runnable runnableAfterFirstAttempt;
+
+ private int totalNumRetries;
+
+ public RetryQueryRunner(
+ QueryRunner<T> baseRunner,
+ BiFunction<Query<T>, List<SegmentDescriptor>, QueryRunner<T>> retryRunnerCreateFn,
+ RetryQueryRunnerConfig config,
+ ObjectMapper jsonMapper
+ )
+ {
+ this(baseRunner, retryRunnerCreateFn, config, jsonMapper, () -> {});
+ }
+
+ /**
+ * Constructor only for testing.
+ */
+ @VisibleForTesting
+ RetryQueryRunner(
+ QueryRunner<T> baseRunner,
+ BiFunction<Query<T>, List<SegmentDescriptor>, QueryRunner<T>> retryRunnerCreateFn,
+ RetryQueryRunnerConfig config,
+ ObjectMapper jsonMapper,
+ Runnable runnableAfterFirstAttempt
+ )
+ {
+ this.baseRunner = baseRunner;
+ this.retryRunnerCreateFn = retryRunnerCreateFn;
+ this.config = config;
+ this.jsonMapper = jsonMapper;
+ this.runnableAfterFirstAttempt = runnableAfterFirstAttempt;
+ }
+
+ @VisibleForTesting
+ int getTotalNumRetries()
+ {
+ return totalNumRetries;
+ }
+
+ @Override
+ public Sequence<T> run(final QueryPlus<T> queryPlus, final ResponseContext context)
+ {
+ return new YieldingSequenceBase<T>()
+ {
+ @Override
+ public <OutType> Yielder<OutType> toYielder(OutType initValue, YieldingAccumulator<OutType, T> accumulator)
+ {
+ final Sequence<Sequence<T>> retryingSequence = new BaseSequence<>(
+ new IteratorMaker<Sequence<T>, RetryingSequenceIterator>()
+ {
+ @Override
+ public RetryingSequenceIterator make()
+ {
+ return new RetryingSequenceIterator(queryPlus, context, baseRunner, runnableAfterFirstAttempt);
+ }
+
+ @Override
+ public void cleanup(RetryingSequenceIterator iterFromMake)
+ {
+ totalNumRetries = iterFromMake.retryCount;
+ }
+ }
+ );
+ return new MergeSequence<>(queryPlus.getQuery().getResultOrdering(), retryingSequence)
+ .toYielder(initValue, accumulator);
+ }
+ };
+ }
+
+ private List<SegmentDescriptor> getMissingSegments(QueryPlus<T> queryPlus, final ResponseContext context)
+ {
+ // Sanity check before retrieving missingSegments from responseContext.
+ // The missingSegments in the responseContext is only valid when all servers have responded to the broker.
+ // The remainingResponses must be not null but 0 in the responseContext at this point.
+ final ConcurrentHashMap<String, Integer> idToRemainingResponses =
+ (ConcurrentHashMap<String, Integer>) Preconditions.checkNotNull(
+ context.get(Key.REMAINING_RESPONSES_FROM_QUERY_SERVERS),
+ "%s in responseContext",
+ Key.REMAINING_RESPONSES_FROM_QUERY_SERVERS.getName()
+ );
+
+ final int remainingResponses = Preconditions.checkNotNull(
+ idToRemainingResponses.get(queryPlus.getQuery().getMostRelevantId()),
+ "Number of remaining responses for query[%s]",
+ queryPlus.getQuery().getMostRelevantId()
+ );
+ if (remainingResponses > 0) {
+ throw new ISE("Failed to check missing segments due to missing responds from [%d] servers", remainingResponses);
+ }
+
+ final Object maybeMissingSegments = context.get(ResponseContext.Key.MISSING_SEGMENTS);
+ if (maybeMissingSegments == null) {
+ return Collections.emptyList();
+ }
+
+ return jsonMapper.convertValue(
+ maybeMissingSegments,
+ new TypeReference<List<SegmentDescriptor>>()
+ {
+ }
+ );
+ }
+
+ /**
+ * A lazy iterator populating {@link Sequence} by retrying the query. The first returned sequence is always the base
+ * sequence from the baseQueryRunner. Subsequent sequences are created dynamically whenever it retries the query. All
+ * the sequences populated by this iterator will be merged (not combined) with the base sequence.
+ *
+ * The design of this iterator depends on how {@link MergeSequence} works; the MergeSequence pops an item from
+ * each underlying sequence and pushes them to a {@link java.util.PriorityQueue}. Whenever it pops from the queue,
+ * it pushes a new item from the sequence where the returned item was originally from. Since the first returned
+ * sequence from this iterator is always the base sequence, the MergeSequence will call {@link Sequence#toYielder}
+ * on the base sequence first which in turn initializing query distribution tree. Once this tree is built, the query
+ * servers (historicals and realtime tasks) will lock all segments to read and report missing segments to the broker.
+ * If there are missing segments reported, this iterator will rewrite the query with those reported segments and
+ * reissue the rewritten query.
+ *
+ * @see org.apache.druid.client.CachingClusteredClient
+ * @see org.apache.druid.client.DirectDruidClient
+ */
+ private class RetryingSequenceIterator implements Iterator<Sequence<T>>
+ {
+ private final QueryPlus<T> queryPlus;
+ private final ResponseContext context;
+ private final QueryRunner<T> baseQueryRunner;
+ private final Runnable runnableAfterFirstAttempt;
+
+ private boolean first = true;
+ private Sequence<T> sequence = null;
+ private int retryCount = 0;
+
+ private RetryingSequenceIterator(
+ QueryPlus<T> queryPlus,
+ ResponseContext context,
+ QueryRunner<T> baseQueryRunner,
+ Runnable runnableAfterFirstAttempt
+ )
+ {
+ this.queryPlus = queryPlus;
+ this.context = context;
+ this.baseQueryRunner = baseQueryRunner;
+ this.runnableAfterFirstAttempt = runnableAfterFirstAttempt;
+ }
+
+ @Override
+ public boolean hasNext()
+ {
+ if (first) {
+ sequence = baseQueryRunner.run(queryPlus, context);
+ // runnableAfterFirstAttempt is only for testing, it must be no-op for production code.
+ runnableAfterFirstAttempt.run();
Review comment:
Hmm, I feel like this could be done without polluting the production code with test stuff.
How about:
* making `RetryingSequenceIterator` visible for testing so you can extend and override `hasNext` to do this runnable thing
* [move building the retry sequence in the run method](https://github.com/apache/druid/pull/10082/files#diff-661e59db1678430f72450fd2fa5ce061R107) into a new method that you can override, so to have it make the test iterator with the runnable instead
##########
File path: server/src/test/java/org/apache/druid/client/CachingClusteredClientTest.java
##########
@@ -497,10 +499,11 @@ public void testTimeseriesCaching()
);
- TimeseriesQuery query = builder.intervals("2011-01-01/2011-01-10")
- .aggregators(RENAMED_AGGS)
- .postAggregators(RENAMED_POST_AGGS)
- .build();
+ TimeseriesQuery query = (TimeseriesQuery) builder.intervals("2011-01-01/2011-01-10")
+ .aggregators(RENAMED_AGGS)
+ .postAggregators(RENAMED_POST_AGGS)
+ .build()
+ .withId("queryId");
Review comment:
I'm surprised that the builder doesn't have an option to set queryId.
##########
File path: processing/src/main/java/org/apache/druid/query/Query.java
##########
@@ -154,6 +161,17 @@ default String getSqlQueryId()
return null;
}
+ /**
+ * Returns a most relevant ID of this query; if it is a subquery, this will return its subquery ID.
+ * If it is a regular query without subqueries, this will return its query ID.
+ * This method should be called after the relevant ID is assigned using {@link #withId} or {@link #withSubQueryId}.
+ */
+ default String getMostRelevantId()
Review comment:
nit: I think `getMostSpecificId()` might be a better name for this method
tangent: it might be nice if the debug logs in `DirectDruidClient` logged both queryId and subQueryId if set
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