Hadoop HDFS源码分析读取命名空间镜像和编辑日志数据

读取命名空间镜像和编辑日志数据

1.读取命名空间镜像

类FSImage是命名空间镜像的java实现，在源码中，英文注释为，

/**
 * FSImage handles checkpointing and logging of the namespace edits.
 *
 */

FSImage.loadFSImage(FSNamesystem, StartupOption, MetaRecoveryContext) 读取命名空间镜像。

  1     private boolean loadFSImage(FSNamesystem target, StartupOption startOpt,
  2                                 MetaRecoveryContext recovery)
  3             throws IOException {
  4         final boolean rollingRollback
  5                 = RollingUpgradeStartupOption.ROLLBACK.matches(startOpt);
  6         final EnumSet<NameNodeFile> nnfs;
  7         if (rollingRollback) {
  8             // if it is rollback of rolling upgrade, only load from the rollback image
  9             nnfs = EnumSet.of(NameNodeFile.IMAGE_ROLLBACK);
 10         } else {
 11             // otherwise we can load from both IMAGE and IMAGE_ROLLBACK
 12             nnfs = EnumSet.of(NameNodeFile.IMAGE, NameNodeFile.IMAGE_ROLLBACK);
 13         }
 14         final FSImageStorageInspector inspector = storage
 15                 .readAndInspectDirs(nnfs, startOpt);
 16 
 17         isUpgradeFinalized = inspector.isUpgradeFinalized();
 18         List<FSImageFile> imageFiles = inspector.getLatestImages();
 19 
 20         StartupProgress prog = NameNode.getStartupProgress();
 21         prog.beginPhase(Phase.LOADING_FSIMAGE);
 22         File phaseFile = imageFiles.get(0).getFile();
 23         prog.setFile(Phase.LOADING_FSIMAGE, phaseFile.getAbsolutePath());
 24         prog.setSize(Phase.LOADING_FSIMAGE, phaseFile.length());
 25         boolean needToSave = inspector.needToSave();
 26 
 27         Iterable<EditLogInputStream> editStreams = null;
 28 
 29         initEditLog(startOpt);
 30 
 31         if (NameNodeLayoutVersion.supports(
 32                 LayoutVersion.Feature.TXID_BASED_LAYOUT, getLayoutVersion())) {
 33             // If we're open for write, we're either non-HA or we're the active NN, so
 34             // we better be able to load all the edits. If we're the standby NN, it's
 35             // OK to not be able to read all of edits right now.
 36             // In the meanwhile, for HA upgrade, we will still write editlog thus need
 37             // this toAtLeastTxId to be set to the max-seen txid
 38             // For rollback in rolling upgrade, we need to set the toAtLeastTxId to
 39             // the txid right before the upgrade marker.
 40             long toAtLeastTxId = editLog.isOpenForWrite() ? inspector
 41                     .getMaxSeenTxId() : 0;
 42             if (rollingRollback) {
 43                 // note that the first image in imageFiles is the special checkpoint
 44                 // for the rolling upgrade
 45                 toAtLeastTxId = imageFiles.get(0).getCheckpointTxId() + 2;
 46             }
 47             editStreams = editLog.selectInputStreams(
 48                     imageFiles.get(0).getCheckpointTxId() + 1,
 49                     toAtLeastTxId, recovery, false);
 50         } else {
 51             editStreams = FSImagePreTransactionalStorageInspector
 52                     .getEditLogStreams(storage);
 53         }
 54         int maxOpSize = conf.getInt(DFSConfigKeys.DFS_NAMENODE_MAX_OP_SIZE_KEY,
 55                 DFSConfigKeys.DFS_NAMENODE_MAX_OP_SIZE_DEFAULT);
 56         for (EditLogInputStream elis : editStreams) {
 57             elis.setMaxOpSize(maxOpSize);
 58         }
 59 
 60         for (EditLogInputStream l : editStreams) {
 61             LOG.debug("Planning to load edit log stream: " + l);
 62         }
 63         if (!editStreams.iterator().hasNext()) {
 64             LOG.info("No edit log streams selected.");
 65         }
 66 
 67         FSImageFile imageFile = null;
 68         for (int i = 0; i < imageFiles.size(); i++) {
 69             try {
 70                 imageFile = imageFiles.get(i);
 71                 loadFSImageFile(target, recovery, imageFile, startOpt);
 72                 break;
 73             } catch (IOException ioe) {
 74                 LOG.error("Failed to load image from " + imageFile, ioe);
 75                 target.clear();
 76                 imageFile = null;
 77             }
 78         }
 79         // Failed to load any images, error out
 80         if (imageFile == null) {
 81             FSEditLog.closeAllStreams(editStreams);
 82             throw new IOException("Failed to load an FSImage file!");
 83         }
 84         prog.endPhase(Phase.LOADING_FSIMAGE);
 85 
 86         if (!rollingRollback) {
 87             long txnsAdvanced = loadEdits(editStreams, target, startOpt, recovery);
 88             needToSave |= needsResaveBasedOnStaleCheckpoint(imageFile.getFile(),
 89                     txnsAdvanced);
 90             if (RollingUpgradeStartupOption.DOWNGRADE.matches(startOpt)) {
 91                 // rename rollback image if it is downgrade
 92                 renameCheckpoint(NameNodeFile.IMAGE_ROLLBACK, NameNodeFile.IMAGE);
 93             }
 94         } else {
 95             // Trigger the rollback for rolling upgrade. Here lastAppliedTxId equals
 96             // to the last txid in rollback fsimage.
 97             rollingRollback(lastAppliedTxId + 1, imageFiles.get(0).getCheckpointTxId());
 98             needToSave = false;
 99         }
100         editLog.setNextTxId(lastAppliedTxId + 1);
101         return needToSave;
102     }

上面的代码中，for循环语句包含的代码用于读入文件的信息。

2.读取编辑日志

读取命名空间镜像后，内存中的名字节点只包含了保存镜像的那一个时刻的内容，还需要读取编辑日志中的内容才能恢复数据。

目前 hdfs 通过 FSEditLogLoader类读取编辑日志。读取的代码如下。

  1 long loadFSEdits(EditLogInputStream edits, long expectedStartingTxId,
  2       StartupOption startOpt, MetaRecoveryContext recovery) throws IOException {
  3     StartupProgress prog = NameNode.getStartupProgress();
  4     Step step = createStartupProgressStep(edits);
  5     prog.beginStep(Phase.LOADING_EDITS, step);
  6     fsNamesys.writeLock();
  7     try {
  8       long startTime = now();
  9       FSImage.LOG.info("Start loading edits file " + edits.getName());
 10       long numEdits = loadEditRecords(edits, false, expectedStartingTxId,
 11           startOpt, recovery);
 12       FSImage.LOG.info("Edits file " + edits.getName() 
 13           + " of size " + edits.length() + " edits # " + numEdits 
 14           + " loaded in " + (now()-startTime)/1000 + " seconds");
 15       return numEdits;
 16     } finally {
 17       edits.close();
 18       fsNamesys.writeUnlock();
 19       prog.endStep(Phase.LOADING_EDITS, step);
 20     }
 21   }
 22 
 23   long loadEditRecords(EditLogInputStream in, boolean closeOnExit,
 24       long expectedStartingTxId, StartupOption startOpt,
 25       MetaRecoveryContext recovery) throws IOException {
 26     FSDirectory fsDir = fsNamesys.dir;
 27 
 28     EnumMap<FSEditLogOpCodes, Holder<Integer>> opCounts =
 29       new EnumMap<FSEditLogOpCodes, Holder<Integer>>(FSEditLogOpCodes.class);
 30 
 31     if (LOG.isTraceEnabled()) {
 32       LOG.trace("Acquiring write lock to replay edit log");
 33     }
 34 
 35     fsNamesys.writeLock();
 36     fsDir.writeLock();
 37 
 38     long recentOpcodeOffsets[] = new long[4];
 39     Arrays.fill(recentOpcodeOffsets, -1);
 40     
 41     long expectedTxId = expectedStartingTxId;
 42     long numEdits = 0;
 43     long lastTxId = in.getLastTxId();
 44     long numTxns = (lastTxId - expectedStartingTxId) + 1;
 45     StartupProgress prog = NameNode.getStartupProgress();
 46     Step step = createStartupProgressStep(in);
 47     prog.setTotal(Phase.LOADING_EDITS, step, numTxns);
 48     Counter counter = prog.getCounter(Phase.LOADING_EDITS, step);
 49     long lastLogTime = now();
 50     long lastInodeId = fsNamesys.getLastInodeId();
 51     
 52     try {
 53       while (true) {
 54         try {
 55           FSEditLogOp op;
 56           try {
 57             op = in.readOp();
 58             if (op == null) {
 59               break;
 60             }
 61           } catch (Throwable e) {
 62             // Handle a problem with our input
 63             check203UpgradeFailure(in.getVersion(true), e);
 64             String errorMessage =
 65               formatEditLogReplayError(in, recentOpcodeOffsets, expectedTxId);
 66             FSImage.LOG.error(errorMessage, e);
 67             if (recovery == null) {
 68                // We will only try to skip over problematic opcodes when in
 69                // recovery mode.
 70               throw new EditLogInputException(errorMessage, e, numEdits);
 71             }
 72             MetaRecoveryContext.editLogLoaderPrompt(
 73                 "We failed to read txId " + expectedTxId,
 74                 recovery, "skipping the bad section in the log");
 75             in.resync();
 76             continue;
 77           }
 78           recentOpcodeOffsets[(int)(numEdits % recentOpcodeOffsets.length)] =
 79             in.getPosition();
 80           if (op.hasTransactionId()) {
 81             if (op.getTransactionId() > expectedTxId) { 
 82               MetaRecoveryContext.editLogLoaderPrompt("There appears " +
 83                   "to be a gap in the edit log.  We expected txid " +
 84                   expectedTxId + ", but got txid " +
 85                   op.getTransactionId() + ".", recovery, "ignoring missing " +
 86                   " transaction IDs");
 87             } else if (op.getTransactionId() < expectedTxId) { 
 88               MetaRecoveryContext.editLogLoaderPrompt("There appears " +
 89                   "to be an out-of-order edit in the edit log.  We " +
 90                   "expected txid " + expectedTxId + ", but got txid " +
 91                   op.getTransactionId() + ".", recovery,
 92                   "skipping the out-of-order edit");
 93               continue;
 94             }
 95           }
 96           try {
 97             if (LOG.isTraceEnabled()) {
 98               LOG.trace("op=" + op + ", startOpt=" + startOpt
 99                   + ", numEdits=" + numEdits + ", totalEdits=" + totalEdits);
100             }
101             long inodeId = applyEditLogOp(op, fsDir, startOpt,
102                 in.getVersion(true), lastInodeId);
103             if (lastInodeId < inodeId) {
104               lastInodeId = inodeId;
105             }
106           } catch (RollingUpgradeOp.RollbackException e) {
107             throw e;
108           } catch (Throwable e) {
109             LOG.error("Encountered exception on operation " + op, e);
110             if (recovery == null) {
111               throw e instanceof IOException? (IOException)e: new IOException(e);
112             }
113 
114             MetaRecoveryContext.editLogLoaderPrompt("Failed to " +
115              "apply edit log operation " + op + ": error " +
116              e.getMessage(), recovery, "applying edits");
117           }
118           // Now that the operation has been successfully decoded and
119           // applied, update our bookkeeping.
120           incrOpCount(op.opCode, opCounts, step, counter);
121           if (op.hasTransactionId()) {
122             lastAppliedTxId = op.getTransactionId();
123             expectedTxId = lastAppliedTxId + 1;
124           } else {
125             expectedTxId = lastAppliedTxId = expectedStartingTxId;
126           }
127           // log progress
128           if (op.hasTransactionId()) {
129             long now = now();
130             if (now - lastLogTime > REPLAY_TRANSACTION_LOG_INTERVAL) {
131               long deltaTxId = lastAppliedTxId - expectedStartingTxId + 1;
132               int percent = Math.round((float) deltaTxId / numTxns * 100);
133               LOG.info("replaying edit log: " + deltaTxId + "/" + numTxns
134                   + " transactions completed. (" + percent + "%)");
135               lastLogTime = now;
136             }
137           }
138           numEdits++;
139           totalEdits++;
140         } catch (RollingUpgradeOp.RollbackException e) {
141           LOG.info("Stopped at OP_START_ROLLING_UPGRADE for rollback.");
142           break;
143         } catch (MetaRecoveryContext.RequestStopException e) {
144           MetaRecoveryContext.LOG.warn("Stopped reading edit log at " +
145               in.getPosition() + "/"  + in.length());
146           break;
147         }
148       }
149     } finally {
150       fsNamesys.resetLastInodeId(lastInodeId);
151       if(closeOnExit) {
152         in.close();
153       }
154       fsDir.writeUnlock();
155       fsNamesys.writeUnlock();
156 
157       if (LOG.isTraceEnabled()) {
158         LOG.trace("replaying edit log finished");
159       }
160 
161       if (FSImage.LOG.isDebugEnabled()) {
162         dumpOpCounts(opCounts);
163       }
164     }
165     return numEdits;
166   }
167

在上述代码while循环中，每次读取EditLogInputStream流中的一个FSEditLogOp。

posted @ 2015-02-22 16:51 birdhack 阅读(1938) 评论(0) 编辑收藏举报

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Hadoop HDFS源码分析读取命名空间镜像和编辑日志数据

读取命名空间镜像和编辑日志数据

1.读取命名空间镜像

2.读取编辑日志

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Hadoop HDFS源码分析 读取命名空间镜像和编辑日志数据

读取命名空间镜像和编辑日志数据

1.读取命名空间镜像

2.读取编辑日志

公告

Hadoop HDFS源码分析读取命名空间镜像和编辑日志数据