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| <pre><span class="source-line-no">001</span><span id="line-1">/*</span> |
| <span class="source-line-no">002</span><span id="line-2"> * Licensed to the Apache Software Foundation (ASF) under one</span> |
| <span class="source-line-no">003</span><span id="line-3"> * or more contributor license agreements. See the NOTICE file</span> |
| <span class="source-line-no">004</span><span id="line-4"> * distributed with this work for additional information</span> |
| <span class="source-line-no">005</span><span id="line-5"> * regarding copyright ownership. The ASF licenses this file</span> |
| <span class="source-line-no">006</span><span id="line-6"> * to you under the Apache License, Version 2.0 (the</span> |
| <span class="source-line-no">007</span><span id="line-7"> * "License"); you may not use this file except in compliance</span> |
| <span class="source-line-no">008</span><span id="line-8"> * with the License. You may obtain a copy of the License at</span> |
| <span class="source-line-no">009</span><span id="line-9"> *</span> |
| <span class="source-line-no">010</span><span id="line-10"> * http://www.apache.org/licenses/LICENSE-2.0</span> |
| <span class="source-line-no">011</span><span id="line-11"> *</span> |
| <span class="source-line-no">012</span><span id="line-12"> * Unless required by applicable law or agreed to in writing, software</span> |
| <span class="source-line-no">013</span><span id="line-13"> * distributed under the License is distributed on an "AS IS" BASIS,</span> |
| <span class="source-line-no">014</span><span id="line-14"> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span> |
| <span class="source-line-no">015</span><span id="line-15"> * See the License for the specific language governing permissions and</span> |
| <span class="source-line-no">016</span><span id="line-16"> * limitations under the License.</span> |
| <span class="source-line-no">017</span><span id="line-17"> */</span> |
| <span class="source-line-no">018</span><span id="line-18">package org.apache.hadoop.hbase.wal;</span> |
| <span class="source-line-no">019</span><span id="line-19"></span> |
| <span class="source-line-no">020</span><span id="line-20">import java.io.Closeable;</span> |
| <span class="source-line-no">021</span><span id="line-21">import java.io.IOException;</span> |
| <span class="source-line-no">022</span><span id="line-22">import org.apache.hadoop.hbase.wal.WAL.Entry;</span> |
| <span class="source-line-no">023</span><span id="line-23">import org.apache.yetus.audience.InterfaceAudience;</span> |
| <span class="source-line-no">024</span><span id="line-24"></span> |
| <span class="source-line-no">025</span><span id="line-25">/**</span> |
| <span class="source-line-no">026</span><span id="line-26"> * A WAL reader which is designed for be able to tailing the WAL file which is currently being</span> |
| <span class="source-line-no">027</span><span id="line-27"> * written. It adds support</span> |
| <span class="source-line-no">028</span><span id="line-28"> */</span> |
| <span class="source-line-no">029</span><span id="line-29">@InterfaceAudience.Private</span> |
| <span class="source-line-no">030</span><span id="line-30">public interface WALTailingReader extends Closeable {</span> |
| <span class="source-line-no">031</span><span id="line-31"></span> |
| <span class="source-line-no">032</span><span id="line-32"> enum State {</span> |
| <span class="source-line-no">033</span><span id="line-33"> /** This means we read an Entry without any error */</span> |
| <span class="source-line-no">034</span><span id="line-34"> NORMAL,</span> |
| <span class="source-line-no">035</span><span id="line-35"> /**</span> |
| <span class="source-line-no">036</span><span id="line-36"> * This means the WAL file has a trailer and we have reached it, which means we have finished</span> |
| <span class="source-line-no">037</span><span id="line-37"> * reading this file normally</span> |
| <span class="source-line-no">038</span><span id="line-38"> */</span> |
| <span class="source-line-no">039</span><span id="line-39"> EOF_WITH_TRAILER,</span> |
| <span class="source-line-no">040</span><span id="line-40"> /**</span> |
| <span class="source-line-no">041</span><span id="line-41"> * This means we meet an error so the upper layer need to reset to read again</span> |
| <span class="source-line-no">042</span><span id="line-42"> */</span> |
| <span class="source-line-no">043</span><span id="line-43"> ERROR_AND_RESET,</span> |
| <span class="source-line-no">044</span><span id="line-44"> /**</span> |
| <span class="source-line-no">045</span><span id="line-45"> * Mostly the same with the above {@link #ERROR_AND_RESET}, the difference is that here we also</span> |
| <span class="source-line-no">046</span><span id="line-46"> * mess up the compression dictionary when reading data, so the upper layer should also clear</span> |
| <span class="source-line-no">047</span><span id="line-47"> * the compression context when reseting, which means when calling resetTo method, we need to</span> |
| <span class="source-line-no">048</span><span id="line-48"> * skip to the position instead of just seek to, which will impact performance.</span> |
| <span class="source-line-no">049</span><span id="line-49"> */</span> |
| <span class="source-line-no">050</span><span id="line-50"> ERROR_AND_RESET_COMPRESSION,</span> |
| <span class="source-line-no">051</span><span id="line-51"> /**</span> |
| <span class="source-line-no">052</span><span id="line-52"> * This means we reach the EOF and the upper layer need to reset to see if there is more data.</span> |
| <span class="source-line-no">053</span><span id="line-53"> * Notice that this does not mean that there is necessarily more data, the upper layer should</span> |
| <span class="source-line-no">054</span><span id="line-54"> * determine whether they need to reset and read again.</span> |
| <span class="source-line-no">055</span><span id="line-55"> */</span> |
| <span class="source-line-no">056</span><span id="line-56"> EOF_AND_RESET,</span> |
| <span class="source-line-no">057</span><span id="line-57"> /**</span> |
| <span class="source-line-no">058</span><span id="line-58"> * Mostly the same with the above {@link #EOF_AND_RESET}, the difference is that here we also</span> |
| <span class="source-line-no">059</span><span id="line-59"> * mess up the compression dictionary when reading data, so the upper layer should also clear</span> |
| <span class="source-line-no">060</span><span id="line-60"> * the compression context when reseting, which means when calling resetTo method, we need to</span> |
| <span class="source-line-no">061</span><span id="line-61"> * skip to the position instead of just seek to, which will impact performance. The</span> |
| <span class="source-line-no">062</span><span id="line-62"> * implementation should try its best to not fall into this situation.</span> |
| <span class="source-line-no">063</span><span id="line-63"> */</span> |
| <span class="source-line-no">064</span><span id="line-64"> EOF_AND_RESET_COMPRESSION;</span> |
| <span class="source-line-no">065</span><span id="line-65"></span> |
| <span class="source-line-no">066</span><span id="line-66"> /**</span> |
| <span class="source-line-no">067</span><span id="line-67"> * A dummy result for returning, as except {@link NORMAL}, for other state we do not need to</span> |
| <span class="source-line-no">068</span><span id="line-68"> * provide fields other than state in the returned {@link Result}.</span> |
| <span class="source-line-no">069</span><span id="line-69"> */</span> |
| <span class="source-line-no">070</span><span id="line-70"> private Result result = new Result(this, null, -1);</span> |
| <span class="source-line-no">071</span><span id="line-71"></span> |
| <span class="source-line-no">072</span><span id="line-72"> public Result getResult() {</span> |
| <span class="source-line-no">073</span><span id="line-73"> return result;</span> |
| <span class="source-line-no">074</span><span id="line-74"> }</span> |
| <span class="source-line-no">075</span><span id="line-75"></span> |
| <span class="source-line-no">076</span><span id="line-76"> public boolean resetCompression() {</span> |
| <span class="source-line-no">077</span><span id="line-77"> return this == ERROR_AND_RESET_COMPRESSION || this == EOF_AND_RESET_COMPRESSION;</span> |
| <span class="source-line-no">078</span><span id="line-78"> }</span> |
| <span class="source-line-no">079</span><span id="line-79"></span> |
| <span class="source-line-no">080</span><span id="line-80"> public boolean eof() {</span> |
| <span class="source-line-no">081</span><span id="line-81"> return this == EOF_AND_RESET || this == EOF_AND_RESET_COMPRESSION || this == EOF_WITH_TRAILER;</span> |
| <span class="source-line-no">082</span><span id="line-82"> }</span> |
| <span class="source-line-no">083</span><span id="line-83"> }</span> |
| <span class="source-line-no">084</span><span id="line-84"></span> |
| <span class="source-line-no">085</span><span id="line-85"> final class Result {</span> |
| <span class="source-line-no">086</span><span id="line-86"></span> |
| <span class="source-line-no">087</span><span id="line-87"> private final State state;</span> |
| <span class="source-line-no">088</span><span id="line-88"> private final Entry entry;</span> |
| <span class="source-line-no">089</span><span id="line-89"> private final long entryEndPos;</span> |
| <span class="source-line-no">090</span><span id="line-90"></span> |
| <span class="source-line-no">091</span><span id="line-91"> public Result(State state, Entry entry, long entryEndPos) {</span> |
| <span class="source-line-no">092</span><span id="line-92"> this.state = state;</span> |
| <span class="source-line-no">093</span><span id="line-93"> this.entry = entry;</span> |
| <span class="source-line-no">094</span><span id="line-94"> this.entryEndPos = entryEndPos;</span> |
| <span class="source-line-no">095</span><span id="line-95"> }</span> |
| <span class="source-line-no">096</span><span id="line-96"></span> |
| <span class="source-line-no">097</span><span id="line-97"> public State getState() {</span> |
| <span class="source-line-no">098</span><span id="line-98"> return state;</span> |
| <span class="source-line-no">099</span><span id="line-99"> }</span> |
| <span class="source-line-no">100</span><span id="line-100"></span> |
| <span class="source-line-no">101</span><span id="line-101"> public Entry getEntry() {</span> |
| <span class="source-line-no">102</span><span id="line-102"> return entry;</span> |
| <span class="source-line-no">103</span><span id="line-103"> }</span> |
| <span class="source-line-no">104</span><span id="line-104"></span> |
| <span class="source-line-no">105</span><span id="line-105"> public long getEntryEndPos() {</span> |
| <span class="source-line-no">106</span><span id="line-106"> return entryEndPos;</span> |
| <span class="source-line-no">107</span><span id="line-107"> }</span> |
| <span class="source-line-no">108</span><span id="line-108"> }</span> |
| <span class="source-line-no">109</span><span id="line-109"></span> |
| <span class="source-line-no">110</span><span id="line-110"> /**</span> |
| <span class="source-line-no">111</span><span id="line-111"> * Read the next entry and make sure the position after reading does not go beyond the given</span> |
| <span class="source-line-no">112</span><span id="line-112"> * {@code limit}.</span> |
| <span class="source-line-no">113</span><span id="line-113"> * <p/></span> |
| <span class="source-line-no">114</span><span id="line-114"> * Notice that we will not throw any checked exception out, all the states are represented by the</span> |
| <span class="source-line-no">115</span><span id="line-115"> * return value. Of course we will log the exceptions out. The reason why we do this is that, for</span> |
| <span class="source-line-no">116</span><span id="line-116"> * tailing a WAL file which is currently being written, we will hit EOFException many times, so it</span> |
| <span class="source-line-no">117</span><span id="line-117"> * should not be considered as an 'exception' and also, creating an Exception is a bit expensive.</span> |
| <span class="source-line-no">118</span><span id="line-118"> * @param limit the position limit. See HBASE-14004 for more details about why we need this</span> |
| <span class="source-line-no">119</span><span id="line-119"> * limitation. -1 means no limit.</span> |
| <span class="source-line-no">120</span><span id="line-120"> */</span> |
| <span class="source-line-no">121</span><span id="line-121"> Result next(long limit);</span> |
| <span class="source-line-no">122</span><span id="line-122"></span> |
| <span class="source-line-no">123</span><span id="line-123"> /**</span> |
| <span class="source-line-no">124</span><span id="line-124"> * Get the current reading position.</span> |
| <span class="source-line-no">125</span><span id="line-125"> */</span> |
| <span class="source-line-no">126</span><span id="line-126"> long getPosition() throws IOException;</span> |
| <span class="source-line-no">127</span><span id="line-127"></span> |
| <span class="source-line-no">128</span><span id="line-128"> /**</span> |
| <span class="source-line-no">129</span><span id="line-129"> * Reopen the reader to see if there is new data arrives, and also seek(or skip) to the given</span> |
| <span class="source-line-no">130</span><span id="line-130"> * position.</span> |
| <span class="source-line-no">131</span><span id="line-131"> * <p/></span> |
| <span class="source-line-no">132</span><span id="line-132"> * If you want to read from the beginning instead of a given position, please pass -1 as</span> |
| <span class="source-line-no">133</span><span id="line-133"> * {@code position}, then the reader will locate to the first entry. Notice that, since we have a</span> |
| <span class="source-line-no">134</span><span id="line-134"> * magic header and a pb header, the first WAL entry is not located at position 0, so passing 0</span> |
| <span class="source-line-no">135</span><span id="line-135"> * will cause trouble.</span> |
| <span class="source-line-no">136</span><span id="line-136"> * @param position the position we want to start reading from after resetting, or -1 if</span> |
| <span class="source-line-no">137</span><span id="line-137"> * you want to start reading from the beginning.</span> |
| <span class="source-line-no">138</span><span id="line-138"> * @param resetCompression whether we also need to clear the compression context. If {@code true},</span> |
| <span class="source-line-no">139</span><span id="line-139"> * we will use skip instead of seek after resetting.</span> |
| <span class="source-line-no">140</span><span id="line-140"> */</span> |
| <span class="source-line-no">141</span><span id="line-141"> void resetTo(long position, boolean resetCompression) throws IOException;</span> |
| <span class="source-line-no">142</span><span id="line-142"></span> |
| <span class="source-line-no">143</span><span id="line-143"> /**</span> |
| <span class="source-line-no">144</span><span id="line-144"> * Override to remove the 'throws IOException' as we are just a reader.</span> |
| <span class="source-line-no">145</span><span id="line-145"> */</span> |
| <span class="source-line-no">146</span><span id="line-146"> @Override</span> |
| <span class="source-line-no">147</span><span id="line-147"> void close();</span> |
| <span class="source-line-no">148</span><span id="line-148">}</span> |
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