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 */ filesUnderSnapshot(final Path snapshotDir)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 */ SnapshotFileCache(Configuration conf, long cacheRefreshPeriod, String refreshThreadName, SnapshotFileInspector inspectSnapshotFiles)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 */ SnapshotFileCache(FileSystem fs, Path rootDir, long cacheRefreshPeriod, long cacheRefreshDelay, String refreshThreadName, SnapshotFileInspector inspectSnapshotFiles)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 */ triggerCacheRefreshForTesting()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. getUnreferencedFiles(Iterable<FileStatus> files)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 refreshCache()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 getSnapshotsInProgress()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 run()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 stop(String why)324 public void stop(String why) { 325 if (!this.stop) { 326 this.stop = true; 327 this.refreshTimer.cancel(); 328 } 329 330 } 331 332 @Override isStopped()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 SnapshotDirectoryInfo(long mtime, Collection<String> files)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 */ getFiles()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 */ hasBeenModified(long mtime)362 public boolean hasBeenModified(long mtime) { 363 return this.lastModified < mtime; 364 } 365 } 366 } 367