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From ivakegg <...@git.apache.org>
Subject [GitHub] accumulo pull request #260: ACCUMULO-4643 initial implementation
Date Tue, 30 May 2017 16:35:27 GMT
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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