Github user joshelser commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/224#discussion_r105268539
--- Diff:
core/src/main/java/org/apache/accumulo/core/client/summary/summarizers/DeletesSummarizer.java
---
@@ -0,0 +1,75 @@
+/*
+ * 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.accumulo.core.client.summary.summarizers;
+
+import org.apache.accumulo.core.client.admin.TableOperations;
+import org.apache.accumulo.core.client.summary.Summarizer;
+import org.apache.accumulo.core.client.summary.SummarizerConfiguration;
+import org.apache.accumulo.core.data.Key;
+import org.apache.accumulo.core.data.Value;
+
+/**
+ * This summarizer tracks the total number of delete Keys seen and the
total number of keys seen.
+ *
+ * <p>
+ * This summarizer is used by
org.apache.accumulo.tserver.compaction.strategies.TooManyDeletesCompactionStrategy
to make compaction decisions based on the
+ * number of deletes.
+ *
+ * @since 2.0.0
+ * @see TableOperations#addSummarizers(String,
org.apache.accumulo.core.client.summary.SummarizerConfiguration...)
+ */
+public class DeletesSummarizer implements Summarizer {
+
+ /**
+ * The name of the statistics for the number of deletes.
+ */
+ public static final String DELETES_STAT = "deletes";
+
+ /**
+ * The name of the statistics for the total number of keys.
+ */
+ public static final String TOTAL_STAT = "total";
+
+ @Override
+ public Collector collector(SummarizerConfiguration sc) {
+ return new Collector() {
+
+ long total = 0;
+ long deletes = 0;
+
+ @Override
+ public void accept(Key k, Value v) {
+ total++;
+ if (k.isDeleted()) {
+ deletes++;
+ }
+ }
+
+ @Override
+ public void summarize(StatisticConsumer sc) {
+ sc.accept(DELETES_STAT, deletes);
+ sc.accept(TOTAL_STAT, total);
+ }
+ };
+ }
+
+ @Override
+ public Combiner combiner(SummarizerConfiguration sc) {
+ return (m1, m2) -> m2.forEach((k, v) -> m1.merge(k, v, Long::sum));
--- End diff --
My guess is that summations would be the most common summaries that we'd
want to do in Accumulo so, even if the boilerplate reduction is small for each,
there might be some long-term gain for all of the uses of summation-summaries.
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