| /** |
| * 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.hadoop.hdfs.server.namenode; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.hdfs.protocol.HdfsConstants; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| |
| /** |
| * A generic abstract class to support reading edits log data from |
| * persistent storage. |
| * |
| * It should stream bytes from the storage exactly as they were written |
| * into the #{@link EditLogOutputStream}. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Evolving |
| public abstract class EditLogInputStream implements Closeable { |
| private FSEditLogOp cachedOp = null; |
| |
| /** |
| * Returns the name of the currently active underlying stream. The default |
| * implementation returns the same value as getName unless overridden by the |
| * subclass. |
| * |
| * @return String name of the currently active underlying stream |
| */ |
| public String getCurrentStreamName() { |
| return getName(); |
| } |
| |
| /** |
| * @return the name of the EditLogInputStream |
| */ |
| public abstract String getName(); |
| |
| /** |
| * @return the first transaction which will be found in this stream |
| */ |
| public abstract long getFirstTxId(); |
| |
| /** |
| * @return the last transaction which will be found in this stream |
| */ |
| public abstract long getLastTxId(); |
| |
| |
| /** |
| * Close the stream. |
| * @throws IOException if an error occurred while closing |
| */ |
| @Override |
| public abstract void close() throws IOException; |
| |
| /** |
| * Read an operation from the stream |
| * @return an operation from the stream or null if at end of stream |
| * @throws IOException if there is an error reading from the stream |
| */ |
| public FSEditLogOp readOp() throws IOException { |
| FSEditLogOp ret; |
| if (cachedOp != null) { |
| ret = cachedOp; |
| cachedOp = null; |
| return ret; |
| } |
| return nextOp(); |
| } |
| |
| /** |
| * Position the stream so that a valid operation can be read from it with |
| * readOp(). |
| * |
| * This method can be used to skip over corrupted sections of edit logs. |
| */ |
| public void resync() { |
| if (cachedOp != null) { |
| return; |
| } |
| cachedOp = nextValidOp(); |
| } |
| |
| /** |
| * Get the next operation from the stream storage. |
| * |
| * @return an operation from the stream or null if at end of stream |
| * @throws IOException if there is an error reading from the stream |
| */ |
| protected abstract FSEditLogOp nextOp() throws IOException; |
| |
| /** |
| * Go through the next operation from the stream storage. |
| * @return the txid of the next operation. |
| */ |
| protected long scanNextOp() throws IOException { |
| FSEditLogOp next = readOp(); |
| return next != null ? next.txid : HdfsConstants.INVALID_TXID; |
| } |
| |
| /** |
| * Get the next valid operation from the stream storage. |
| * |
| * This is exactly like nextOp, except that we attempt to skip over damaged |
| * parts of the edit log |
| * |
| * @return an operation from the stream or null if at end of stream |
| */ |
| protected FSEditLogOp nextValidOp() { |
| // This is a trivial implementation which just assumes that any errors mean |
| // that there is nothing more of value in the log. Subclasses that support |
| // error recovery will want to override this. |
| try { |
| return nextOp(); |
| } catch (Throwable e) { |
| return null; |
| } |
| } |
| |
| /** |
| * Skip edit log operations up to a given transaction ID, or until the |
| * end of the edit log is reached. |
| * |
| * After this function returns, the next call to readOp will return either |
| * end-of-file (null) or a transaction with a txid equal to or higher than |
| * the one we asked for. |
| * |
| * @param txid The transaction ID to read up until. |
| * @return Returns true if we found a transaction ID greater than |
| * or equal to 'txid' in the log. |
| */ |
| public boolean skipUntil(long txid) throws IOException { |
| while (true) { |
| FSEditLogOp op = readOp(); |
| if (op == null) { |
| return false; |
| } |
| if (op.getTransactionId() >= txid) { |
| cachedOp = op; |
| return true; |
| } |
| } |
| } |
| |
| /** |
| * return the cachedOp, and reset it to null. |
| */ |
| FSEditLogOp getCachedOp() { |
| FSEditLogOp op = this.cachedOp; |
| cachedOp = null; |
| return op; |
| } |
| |
| /** |
| * Get the layout version of the data in the stream. |
| * @return the layout version of the ops in the stream. |
| * @throws IOException if there is an error reading the version |
| */ |
| public abstract int getVersion(boolean verifyVersion) throws IOException; |
| |
| /** |
| * Get the "position" of in the stream. This is useful for |
| * debugging and operational purposes. |
| * |
| * Different stream types can have a different meaning for |
| * what the position is. For file streams it means the byte offset |
| * from the start of the file. |
| * |
| * @return the position in the stream |
| */ |
| public abstract long getPosition(); |
| |
| /** |
| * Return the size of the current edits log or -1 if unknown. |
| * |
| * @return long size of the current edits log or -1 if unknown |
| */ |
| public abstract long length() throws IOException; |
| |
| /** |
| * Return true if this stream is in progress, false if it is finalized. |
| */ |
| public abstract boolean isInProgress(); |
| |
| /** |
| * Set the maximum opcode size in bytes. |
| */ |
| public abstract void setMaxOpSize(int maxOpSize); |
| } |