Github user keith-turner commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/46#discussion_r39518313
--- Diff: core/src/main/java/org/apache/accumulo/core/sample/Sampler.java
---
@@ -0,0 +1,45 @@
+/*
+ * 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.sample;
+
+import org.apache.accumulo.core.client.admin.SamplerConfiguration;
+import org.apache.accumulo.core.data.Key;
+
+/**
+ * A function that decides which key values are stored in a tables sample.
As Accumuo compacts data and creates rfiles it uses a Sampler to decided what to
+ * store in the rfiles sample section. The class name of the Sampler and
the Samplers configuration are stored in each rfile. A scan of a tables sample
will
+ * only succeed if all rfiles were created with the same sampler and
sampler configuration.
+ *
+ * <p>
+ * Since the decisions that Sampler makes are persisted, the behavior of a
Sampler for a given configuration should always be the same. One way to offer a
new
+ * behavior is to offer new options, while still supporting old behavior
with a Samplers existing options.
+ *
+ * <p>
+ * Ideally a sampler that selects a Key k1 would also select updates for
k1. For example if a Sampler selects :
+ * {@code row='000989' family='name' qualifier='last' visibility='ADMIN'
time=9 value='Doe'}, it would be nice if it also selected :
+ * {@code row='000989' family='name' qualifier='last' visibility='ADMIN'
time=20 value='Dough'}. Using hash and modulo on the key fields is a good way to
+ * accomplish this and {@link AbstractHashSampler} provides a good basis
for implementation.
+ *
+ * @since 1.8.0
+ */
+
+public interface Sampler {
+ void init(SamplerConfiguration config);
+
+ boolean accept(Key k);
--- End diff --
Added javadoc in 3d0be31
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