1 /**
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.apache.hadoop.hbase.master.snapshot;
19
20 import java.io.FileNotFoundException;
21 import java.io.IOException;
22 import java.util.Collection;
23 import java.util.HashMap;
24 import java.util.HashSet;
25 import java.util.List;
26 import java.util.Map;
27 import java.util.Set;
28 import java.util.Timer;
29 import java.util.TimerTask;
30
31 import com.google.common.annotations.VisibleForTesting;
32 import com.google.common.collect.Lists;
33 import org.apache.commons.logging.Log;
34 import org.apache.commons.logging.LogFactory;
35 import org.apache.hadoop.hbase.classification.InterfaceAudience;
36 import org.apache.hadoop.hbase.classification.InterfaceStability;
37 import org.apache.hadoop.conf.Configuration;
38 import org.apache.hadoop.fs.FileStatus;
39 import org.apache.hadoop.fs.FileSystem;
40 import org.apache.hadoop.fs.Path;
41 import org.apache.hadoop.hbase.Stoppable;
42 import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
43 import org.apache.hadoop.hbase.util.FSUtils;
44
45 /**
46 * Intelligently keep track of all the files for all the snapshots.
47 * <p>
48 * A cache of files is kept to avoid querying the {@link FileSystem} frequently. If there is a cache
49 * miss the directory modification time is used to ensure that we don't rescan directories that we
50 * already have in cache. We only check the modification times of the snapshot directories
51 * (/hbase/.snapshot/[snapshot_name]) to determine if the files need to be loaded into the cache.
52 * <p>
53 * New snapshots will be added to the cache and deleted snapshots will be removed when we refresh
54 * the cache. If the files underneath a snapshot directory are changed, but not the snapshot itself,
55 * we will ignore updates to that snapshot's files.
56 * <p>
57 * This is sufficient because each snapshot has its own directory and is added via an atomic rename
58 * <i>once</i>, when the snapshot is created. We don't need to worry about the data in the snapshot
59 * being run.
60 * <p>
61 * Further, the cache is periodically refreshed ensure that files in snapshots that were deleted are
62 * also removed from the cache.
63 * <p>
64 * A {@link SnapshotFileCache.SnapshotFileInspector} must be passed when creating <tt>this</tt> to
65 * allow extraction of files under /hbase/.snapshot/[snapshot name] directory, for each snapshot.
66 * This allows you to only cache files under, for instance, all the logs in the .logs directory or
67 * all the files under all the regions.
68 * <p>
69 * <tt>this</tt> also considers all running snapshots (those under /hbase/.snapshot/.tmp) as valid
70 * snapshots and will attempt to cache files from those snapshots as well.
71 * <p>
72 * Queries about a given file are thread-safe with respect to multiple queries and cache refreshes.
73 */
74 @InterfaceAudience.Private
75 @InterfaceStability.Evolving
76 public class SnapshotFileCache implements Stoppable {
77 interface SnapshotFileInspector {
78 /**
79 * Returns a collection of file names needed by the snapshot.
80 * @param snapshotDir {@link Path} to the snapshot directory to scan.
81 * @return the collection of file names needed by the snapshot.
82 */
83 Collection<String> filesUnderSnapshot(final Path snapshotDir) throws IOException;
84 }
85
86 private static final Log LOG = LogFactory.getLog(SnapshotFileCache.class);
87 private volatile boolean stop = false;
88 private final FileSystem fs;
89 private final SnapshotFileInspector fileInspector;
90 private final Path snapshotDir;
91 private final Set<String> cache = new HashSet<String>();
92 /**
93 * This is a helper map of information about the snapshot directories so we don't need to rescan
94 * them if they haven't changed since the last time we looked.
95 */
96 private final Map<String, SnapshotDirectoryInfo> snapshots =
97 new HashMap<String, SnapshotDirectoryInfo>();
98 private final Timer refreshTimer;
99
100 private long lastModifiedTime = Long.MIN_VALUE;
101
102 /**
103 * Create a snapshot file cache for all snapshots under the specified [root]/.snapshot on the
104 * filesystem.
105 * <p>
106 * Immediately loads the file cache.
107 * @param conf to extract the configured {@link FileSystem} where the snapshots are stored and
108 * hbase root directory
109 * @param cacheRefreshPeriod frequency (ms) with which the cache should be refreshed
110 * @param refreshThreadName name of the cache refresh thread
111 * @param inspectSnapshotFiles Filter to apply to each snapshot to extract the files.
112 * @throws IOException if the {@link FileSystem} or root directory cannot be loaded
113 */
114 public SnapshotFileCache(Configuration conf, long cacheRefreshPeriod, String refreshThreadName,
115 SnapshotFileInspector inspectSnapshotFiles) throws IOException {
116 this(FSUtils.getCurrentFileSystem(conf), FSUtils.getRootDir(conf), 0, cacheRefreshPeriod,
117 refreshThreadName, inspectSnapshotFiles);
118 }
119
120 /**
121 * Create a snapshot file cache for all snapshots under the specified [root]/.snapshot on the
122 * filesystem
123 * @param fs {@link FileSystem} where the snapshots are stored
124 * @param rootDir hbase root directory
125 * @param cacheRefreshPeriod period (ms) with which the cache should be refreshed
126 * @param cacheRefreshDelay amount of time to wait for the cache to be refreshed
127 * @param refreshThreadName name of the cache refresh thread
128 * @param inspectSnapshotFiles Filter to apply to each snapshot to extract the files.
129 */
130 public SnapshotFileCache(FileSystem fs, Path rootDir, long cacheRefreshPeriod,
131 long cacheRefreshDelay, String refreshThreadName, SnapshotFileInspector inspectSnapshotFiles) {
132 this.fs = fs;
133 this.fileInspector = inspectSnapshotFiles;
134 this.snapshotDir = SnapshotDescriptionUtils.getSnapshotsDir(rootDir);
135 // periodically refresh the file cache to make sure we aren't superfluously saving files.
136 this.refreshTimer = new Timer(refreshThreadName, true);
137 this.refreshTimer.scheduleAtFixedRate(new RefreshCacheTask(), cacheRefreshDelay,
138 cacheRefreshPeriod);
139 }
140
141 /**
142 * Trigger a cache refresh, even if its before the next cache refresh. Does not affect pending
143 * cache refreshes.
144 * <p>
145 * Blocks until the cache is refreshed.
146 * <p>
147 * Exposed for TESTING.
148 */
149 public void triggerCacheRefreshForTesting() {
150 try {
151 SnapshotFileCache.this.refreshCache();
152 } catch (IOException e) {
153 LOG.warn("Failed to refresh snapshot hfile cache!", e);
154 }
155 LOG.debug("Current cache:" + cache);
156 }
157
158 /**
159 * Check to see if any of the passed file names is contained in any of the snapshots.
160 * First checks an in-memory cache of the files to keep. If its not in the cache, then the cache
161 * is refreshed and the cache checked again for that file.
162 * This ensures that we never return files that exist.
163 * <p>
164 * Note this may lead to periodic false positives for the file being referenced. Periodically, the
165 * cache is refreshed even if there are no requests to ensure that the false negatives get removed
166 * eventually. For instance, suppose you have a file in the snapshot and it gets loaded into the
167 * cache. Then at some point later that snapshot is deleted. If the cache has not been refreshed
168 * at that point, cache will still think the file system contains that file and return
169 * <tt>true</tt>, even if it is no longer present (false positive). However, if the file never was
170 * on the filesystem, we will never find it and always return <tt>false</tt>.
171 * @param files file to check, NOTE: Relies that files are loaded from hdfs before method
172 * is called (NOT LAZY)
173 * @return <tt>unReferencedFiles</tt> the collection of files that do not have snapshot references
174 * @throws IOException if there is an unexpected error reaching the filesystem.
175 */
176 // XXX this is inefficient to synchronize on the method, when what we really need to guard against
177 // is an illegal access to the cache. Really we could do a mutex-guarded pointer swap on the
178 // cache, but that seems overkill at the moment and isn't necessarily a bottleneck.
179 public synchronized Iterable<FileStatus> getUnreferencedFiles(Iterable<FileStatus> files)
180 throws IOException {
181 List<FileStatus> unReferencedFiles = Lists.newArrayList();
182 List<String> snapshotsInProgress = null;
183 boolean refreshed = false;
184 for (FileStatus file : files) {
185 String fileName = file.getPath().getName();
186 if (!refreshed && !cache.contains(fileName)) {
187 refreshCache();
188 refreshed = true;
189 }
190 if (cache.contains(fileName)) {
191 continue;
192 }
193 if (snapshotsInProgress == null) {
194 snapshotsInProgress = getSnapshotsInProgress();
195 }
196 if (snapshotsInProgress.contains(fileName)) {
197 continue;
198 }
199 unReferencedFiles.add(file);
200 }
201 return unReferencedFiles;
202 }
203
204 private synchronized void refreshCache() throws IOException {
205 long lastTimestamp = Long.MAX_VALUE;
206 boolean hasChanges = false;
207
208 // get the status of the snapshots directory and check if it is has changes
209 try {
210 FileStatus dirStatus = fs.getFileStatus(snapshotDir);
211 lastTimestamp = dirStatus.getModificationTime();
212 hasChanges |= (lastTimestamp >= lastModifiedTime);
213 } catch (FileNotFoundException e) {
214 if (this.cache.size() > 0) {
215 LOG.error("Snapshot directory: " + snapshotDir + " doesn't exist");
216 }
217 return;
218 }
219
220 // get the status of the snapshots temporary directory and check if it has changes
221 // The top-level directory timestamp is not updated, so we have to check the inner-level.
222 try {
223 Path snapshotTmpDir = new Path(snapshotDir, SnapshotDescriptionUtils.SNAPSHOT_TMP_DIR_NAME);
224 FileStatus tempDirStatus = fs.getFileStatus(snapshotTmpDir);
225 lastTimestamp = Math.min(lastTimestamp, tempDirStatus.getModificationTime());
226 hasChanges |= (lastTimestamp >= lastModifiedTime);
227 if (!hasChanges) {
228 FileStatus[] tmpSnapshots = FSUtils.listStatus(fs, snapshotDir);
229 if (tmpSnapshots != null) {
230 for (FileStatus dirStatus: tmpSnapshots) {
231 lastTimestamp = Math.min(lastTimestamp, dirStatus.getModificationTime());
232 }
233 hasChanges |= (lastTimestamp >= lastModifiedTime);
234 }
235 }
236 } catch (FileNotFoundException e) {
237 // Nothing todo, if the tmp dir is empty
238 }
239
240 // if the snapshot directory wasn't modified since we last check, we are done
241 if (!hasChanges) {
242 return;
243 }
244
245 // directory was modified, so we need to reload our cache
246 // there could be a slight race here where we miss the cache, check the directory modification
247 // time, then someone updates the directory, causing us to not scan the directory again.
248 // However, snapshot directories are only created once, so this isn't an issue.
249
250 // 1. update the modified time
251 this.lastModifiedTime = lastTimestamp;
252
253 // 2.clear the cache
254 this.cache.clear();
255 Map<String, SnapshotDirectoryInfo> known = new HashMap<String, SnapshotDirectoryInfo>();
256
257 // 3. check each of the snapshot directories
258 FileStatus[] snapshots = FSUtils.listStatus(fs, snapshotDir);
259 if (snapshots == null) {
260 // remove all the remembered snapshots because we don't have any left
261 if (LOG.isDebugEnabled() && this.snapshots.size() > 0) {
262 LOG.debug("No snapshots on-disk, cache empty");
263 }
264 this.snapshots.clear();
265 return;
266 }
267
268 // 3.1 iterate through the on-disk snapshots
269 for (FileStatus snapshot : snapshots) {
270 String name = snapshot.getPath().getName();
271 // its not the tmp dir,
272 if (!name.equals(SnapshotDescriptionUtils.SNAPSHOT_TMP_DIR_NAME)) {
273 SnapshotDirectoryInfo files = this.snapshots.remove(name);
274 // 3.1.1 if we don't know about the snapshot or its been modified, we need to update the
275 // files the latter could occur where I create a snapshot, then delete it, and then make a
276 // new snapshot with the same name. We will need to update the cache the information from
277 // that new snapshot, even though it has the same name as the files referenced have
278 // probably changed.
279 if (files == null || files.hasBeenModified(snapshot.getModificationTime())) {
280 // get all files for the snapshot and create a new info
281 Collection<String> storedFiles = fileInspector.filesUnderSnapshot(snapshot.getPath());
282 files = new SnapshotDirectoryInfo(snapshot.getModificationTime(), storedFiles);
283 }
284 // 3.2 add all the files to cache
285 this.cache.addAll(files.getFiles());
286 known.put(name, files);
287 }
288 }
289
290 // 4. set the snapshots we are tracking
291 this.snapshots.clear();
292 this.snapshots.putAll(known);
293 }
294
295 @VisibleForTesting List<String> getSnapshotsInProgress() throws IOException {
296 List<String> snapshotInProgress = Lists.newArrayList();
297 // only add those files to the cache, but not to the known snapshots
298 Path snapshotTmpDir = new Path(snapshotDir, SnapshotDescriptionUtils.SNAPSHOT_TMP_DIR_NAME);
299 // only add those files to the cache, but not to the known snapshots
300 FileStatus[] running = FSUtils.listStatus(fs, snapshotTmpDir);
301 if (running != null) {
302 for (FileStatus run : running) {
303 snapshotInProgress.addAll(fileInspector.filesUnderSnapshot(run.getPath()));
304 }
305 }
306 return snapshotInProgress;
307 }
308
309 /**
310 * Simple helper task that just periodically attempts to refresh the cache
311 */
312 public class RefreshCacheTask extends TimerTask {
313 @Override
314 public void run() {
315 try {
316 SnapshotFileCache.this.refreshCache();
317 } catch (IOException e) {
318 LOG.warn("Failed to refresh snapshot hfile cache!", e);
319 }
320 }
321 }
322
323 @Override
324 public void stop(String why) {
325 if (!this.stop) {
326 this.stop = true;
327 this.refreshTimer.cancel();
328 }
329
330 }
331
332 @Override
333 public boolean isStopped() {
334 return this.stop;
335 }
336
337 /**
338 * Information about a snapshot directory
339 */
340 private static class SnapshotDirectoryInfo {
341 long lastModified;
342 Collection<String> files;
343
344 public SnapshotDirectoryInfo(long mtime, Collection<String> files) {
345 this.lastModified = mtime;
346 this.files = files;
347 }
348
349 /**
350 * @return the hfiles in the snapshot when <tt>this</tt> was made.
351 */
352 public Collection<String> getFiles() {
353 return this.files;
354 }
355
356 /**
357 * Check if the snapshot directory has been modified
358 * @param mtime current modification time of the directory
359 * @return <tt>true</tt> if it the modification time of the directory is newer time when we
360 * created <tt>this</tt>
361 */
362 public boolean hasBeenModified(long mtime) {
363 return this.lastModified < mtime;
364 }
365 }
366 }