1 /**
2 *
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19
20 package org.apache.hadoop.hbase.wal;
21
22 import java.io.Closeable;
23 import java.io.IOException;
24 import java.util.Set;
25
26 import org.apache.hadoop.hbase.HConstants;
27 import org.apache.hadoop.hbase.HRegionInfo;
28 import org.apache.hadoop.hbase.HTableDescriptor;
29 import org.apache.hadoop.hbase.classification.InterfaceAudience;
30 import org.apache.hadoop.hbase.classification.InterfaceStability;
31 // imports we use from yet-to-be-moved regionsever.wal
32 import org.apache.hadoop.hbase.regionserver.wal.CompressionContext;
33 import org.apache.hadoop.hbase.regionserver.wal.FailedLogCloseException;
34 import org.apache.hadoop.hbase.regionserver.wal.HLogKey;
35 import org.apache.hadoop.hbase.regionserver.wal.WALActionsListener;
36 import org.apache.hadoop.hbase.regionserver.wal.WALCoprocessorHost;
37 import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
38
39 import com.google.common.annotations.VisibleForTesting;
40
41 /**
42 * A Write Ahead Log (WAL) provides service for reading, writing waledits. This interface provides
43 * APIs for WAL users (such as RegionServer) to use the WAL (do append, sync, etc).
44 *
45 * Note that some internals, such as log rolling and performance evaluation tools, will use
46 * WAL.equals to determine if they have already seen a given WAL.
47 */
48 @InterfaceAudience.Private
49 @InterfaceStability.Evolving
50 public interface WAL extends Closeable {
51
52 /**
53 * Registers WALActionsListener
54 */
55 void registerWALActionsListener(final WALActionsListener listener);
56
57 /**
58 * Unregisters WALActionsListener
59 */
60 boolean unregisterWALActionsListener(final WALActionsListener listener);
61
62 /**
63 * Roll the log writer. That is, start writing log messages to a new file.
64 *
65 * <p>
66 * The implementation is synchronized in order to make sure there's one rollWriter
67 * running at any given time.
68 *
69 * @return If lots of logs, flush the returned regions so next time through we
70 * can clean logs. Returns null if nothing to flush. Names are actual
71 * region names as returned by {@link HRegionInfo#getEncodedName()}
72 */
73 byte[][] rollWriter() throws FailedLogCloseException, IOException;
74
75 /**
76 * Roll the log writer. That is, start writing log messages to a new file.
77 *
78 * <p>
79 * The implementation is synchronized in order to make sure there's one rollWriter
80 * running at any given time.
81 *
82 * @param force
83 * If true, force creation of a new writer even if no entries have
84 * been written to the current writer
85 * @return If lots of logs, flush the returned regions so next time through we
86 * can clean logs. Returns null if nothing to flush. Names are actual
87 * region names as returned by {@link HRegionInfo#getEncodedName()}
88 */
89 byte[][] rollWriter(boolean force) throws FailedLogCloseException, IOException;
90
91 /**
92 * Stop accepting new writes. If we have unsynced writes still in buffer, sync them.
93 * Extant edits are left in place in backing storage to be replayed later.
94 */
95 void shutdown() throws IOException;
96
97 /**
98 * Caller no longer needs any edits from this WAL. Implementers are free to reclaim
99 * underlying resources after this call; i.e. filesystem based WALs can archive or
100 * delete files.
101 */
102 @Override
103 void close() throws IOException;
104
105 /**
106 * Append a set of edits to the WAL. The WAL is not flushed/sync'd after this transaction
107 * completes BUT on return this edit must have its region edit/sequence id assigned
108 * else it messes up our unification of mvcc and sequenceid. On return <code>key</code> will
109 * have the region edit/sequence id filled in.
110 * @param info
111 * @param key Modified by this call; we add to it this edits region edit/sequence id.
112 * @param edits Edits to append. MAY CONTAIN NO EDITS for case where we want to get an edit
113 * sequence id that is after all currently appended edits.
114 * @param htd used to give scope for replication TODO refactor out in favor of table name and
115 * info
116 * @param inMemstore Always true except for case where we are writing a compaction completion
117 * record into the WAL; in this case the entry is just so we can finish an unfinished compaction
118 * -- it is not an edit for memstore.
119 * @return Returns a 'transaction id' and <code>key</code> will have the region edit/sequence id
120 * in it.
121 */
122 long append(HTableDescriptor htd, HRegionInfo info, WALKey key, WALEdit edits,
123 boolean inMemstore)
124 throws IOException;
125
126 /**
127 * Sync what we have in the WAL.
128 * @throws IOException
129 */
130 void sync() throws IOException;
131
132 /**
133 * Sync the WAL if the txId was not already sync'd.
134 * @param txid Transaction id to sync to.
135 * @throws IOException
136 */
137 void sync(long txid) throws IOException;
138
139 /**
140 * WAL keeps track of the sequence numbers that are as yet not flushed im memstores
141 * in order to be able to do accounting to figure which WALs can be let go. This method tells WAL
142 * that some region is about to flush. The flush can be the whole region or for a column family
143 * of the region only.
144 *
145 * <p>Currently, it is expected that the update lock is held for the region; i.e. no
146 * concurrent appends while we set up cache flush.
147 * @param families Families to flush. May be a subset of all families in the region.
148 * @return Returns {@link HConstants#NO_SEQNUM} if we are flushing the whole region OR if
149 * we are flushing a subset of all families but there are no edits in those families not
150 * being flushed; in other words, this is effectively same as a flush of all of the region
151 * though we were passed a subset of regions. Otherwise, it returns the sequence id of the
152 * oldest/lowest outstanding edit.
153 * @see #completeCacheFlush(byte[])
154 * @see #abortCacheFlush(byte[])
155 */
156 Long startCacheFlush(final byte[] encodedRegionName, Set<byte[]> families);
157
158 /**
159 * Complete the cache flush.
160 * @param encodedRegionName Encoded region name.
161 * @see #startCacheFlush(byte[], Set)
162 * @see #abortCacheFlush(byte[])
163 */
164 void completeCacheFlush(final byte[] encodedRegionName);
165
166 /**
167 * Abort a cache flush. Call if the flush fails. Note that the only recovery
168 * for an aborted flush currently is a restart of the regionserver so the
169 * snapshot content dropped by the failure gets restored to the memstore.
170 * @param encodedRegionName Encoded region name.
171 */
172 void abortCacheFlush(byte[] encodedRegionName);
173
174 /**
175 * @return Coprocessor host.
176 */
177 WALCoprocessorHost getCoprocessorHost();
178
179 /**
180 * Gets the earliest unflushed sequence id in the memstore for the region.
181 * @param encodedRegionName The region to get the number for.
182 * @return The earliest/lowest/oldest sequence id if present, HConstants.NO_SEQNUM if absent.
183 * @deprecated Since version 1.2.0. Removing because not used and exposes subtle internal
184 * workings. Use {@link #getEarliestMemstoreSeqNum(byte[], byte[])}
185 */
186 @VisibleForTesting
187 @Deprecated
188 long getEarliestMemstoreSeqNum(byte[] encodedRegionName);
189
190 /**
191 * Gets the earliest unflushed sequence id in the memstore for the store.
192 * @param encodedRegionName The region to get the number for.
193 * @param familyName The family to get the number for.
194 * @return The earliest/lowest/oldest sequence id if present, HConstants.NO_SEQNUM if absent.
195 */
196 long getEarliestMemstoreSeqNum(byte[] encodedRegionName, byte[] familyName);
197
198 /**
199 * Human readable identifying information about the state of this WAL.
200 * Implementors are encouraged to include information appropriate for debugging.
201 * Consumers are advised not to rely on the details of the returned String; it does
202 * not have a defined structure.
203 */
204 @Override
205 String toString();
206
207 /**
208 * When outside clients need to consume persisted WALs, they rely on a provided
209 * Reader.
210 */
211 interface Reader extends Closeable {
212 Entry next() throws IOException;
213 Entry next(Entry reuse) throws IOException;
214 void seek(long pos) throws IOException;
215 long getPosition() throws IOException;
216 void reset() throws IOException;
217 }
218
219 /**
220 * Utility class that lets us keep track of the edit with it's key.
221 */
222 class Entry {
223 private WALEdit edit;
224 private WALKey key;
225
226 public Entry() {
227 edit = new WALEdit();
228 // we use HLogKey here instead of WALKey directly to support legacy coprocessors.
229 key = new HLogKey();
230 }
231
232 /**
233 * Constructor for both params
234 *
235 * @param edit log's edit
236 * @param key log's key
237 */
238 public Entry(WALKey key, WALEdit edit) {
239 super();
240 this.key = key;
241 this.edit = edit;
242 }
243
244 /**
245 * Gets the edit
246 *
247 * @return edit
248 */
249 public WALEdit getEdit() {
250 return edit;
251 }
252
253 /**
254 * Gets the key
255 *
256 * @return key
257 */
258 public WALKey getKey() {
259 return key;
260 }
261
262 /**
263 * Set compression context for this entry.
264 *
265 * @param compressionContext
266 * Compression context
267 */
268 public void setCompressionContext(CompressionContext compressionContext) {
269 edit.setCompressionContext(compressionContext);
270 key.setCompressionContext(compressionContext);
271 }
272
273 @Override
274 public String toString() {
275 return this.key + "=" + this.edit;
276 }
277
278 }
279
280 }