Github user ivakegg commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/260#discussion_r119151013
--- Diff:
core/src/main/java/org/apache/accumulo/core/iterators/user/ScanYieldException.java
---
@@ -0,0 +1,35 @@
+/*
+ * 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.iterators.user;
+
+import org.apache.accumulo.core.data.Key;
+
+/**
+ * This exception can be thrown at from a next or seek call on an iterator
to allow other scans to get time slots. This mechanism is intended to avoid a
set of
+ * scans to dominate all of the scan slots (readahead threads) and starve
other scans out.
+ */
+public class ScanYieldException extends RuntimeException {
+ private final Key position;
+
+ public ScanYieldException(Key position) {
--- End diff --
You make a good point of making SKVI more "user-friendly". I am
considering writing an alternative implementation where I will create a
yielding SKVI interface which adds a method to specify whether the the last
next or seek call yielded control before finding the next top key, and a method
to return the key where we decided to yield control. This way the initial SKVI
api would not change and we would not be using exceptions for flow-control.
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