Java tutorial
/** * * 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.hbase.regionserver.handler; import java.io.IOException; import java.util.concurrent.atomic.AtomicBoolean; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.hbase.HRegionInfo; import org.apache.hadoop.hbase.HTableDescriptor; import org.apache.hadoop.hbase.Server; import org.apache.hadoop.hbase.executor.EventHandler; import org.apache.hadoop.hbase.executor.EventType; import org.apache.hadoop.hbase.regionserver.HRegion; import org.apache.hadoop.hbase.regionserver.RegionServerAccounting; import org.apache.hadoop.hbase.regionserver.RegionServerServices; import org.apache.hadoop.hbase.util.CancelableProgressable; import org.apache.hadoop.hbase.zookeeper.ZKAssign; import org.apache.hadoop.hbase.zookeeper.ZKUtil; import org.apache.zookeeper.KeeperException; /** * Handles opening of a region on a region server. * <p> * This is executed after receiving an OPEN RPC from the master or client. */ @InterfaceAudience.Private public class OpenRegionHandler extends EventHandler { private static final Log LOG = LogFactory.getLog(OpenRegionHandler.class); protected final RegionServerServices rsServices; private final HRegionInfo regionInfo; private final HTableDescriptor htd; // We get version of our znode at start of open process and monitor it across // the total open. We'll fail the open if someone hijacks our znode; we can // tell this has happened if version is not as expected. private volatile int version = -1; //version of the offline node that was set by the master private volatile int versionOfOfflineNode = -1; public OpenRegionHandler(final Server server, final RegionServerServices rsServices, HRegionInfo regionInfo, HTableDescriptor htd) { this(server, rsServices, regionInfo, htd, EventType.M_RS_OPEN_REGION, -1); } public OpenRegionHandler(final Server server, final RegionServerServices rsServices, HRegionInfo regionInfo, HTableDescriptor htd, int versionOfOfflineNode) { this(server, rsServices, regionInfo, htd, EventType.M_RS_OPEN_REGION, versionOfOfflineNode); } protected OpenRegionHandler(final Server server, final RegionServerServices rsServices, final HRegionInfo regionInfo, final HTableDescriptor htd, EventType eventType, final int versionOfOfflineNode) { super(server, eventType); this.rsServices = rsServices; this.regionInfo = regionInfo; this.htd = htd; this.versionOfOfflineNode = versionOfOfflineNode; } public HRegionInfo getRegionInfo() { return regionInfo; } @Override public void process() throws IOException { boolean openSuccessful = false; boolean transitionedToOpening = false; final String regionName = regionInfo.getRegionNameAsString(); HRegion region = null; try { if (this.server.isStopped() || this.rsServices.isStopping()) { return; } final String encodedName = regionInfo.getEncodedName(); // 3 different difficult situations can occur // 1) The opening was cancelled. This is an expected situation // 2) The region was hijacked, we no longer have the znode // 3) The region is now marked as online while we're suppose to open. This would be a bug. // Check that this region is not already online if (this.rsServices.getFromOnlineRegions(encodedName) != null) { LOG.error("Region " + encodedName + " was already online when we started processing the opening. " + "Marking this new attempt as failed"); return; } // Check that we're still supposed to open the region and transition. // If fails, just return. Someone stole the region from under us. // Calling transitionZookeeperOfflineToOpening initializes this.version. if (!isRegionStillOpening()) { LOG.error("Region " + encodedName + " opening cancelled"); return; } if (!transitionZookeeperOfflineToOpening(encodedName, versionOfOfflineNode)) { LOG.warn("Region was hijacked? Opening cancelled for encodedName=" + encodedName); // This is a desperate attempt: the znode is unlikely to be ours. But we can't do more. return; } transitionedToOpening = true; // Open region. After a successful open, failures in subsequent // processing needs to do a close as part of cleanup. region = openRegion(); if (region == null) { return; } boolean failed = true; if (tickleOpening("post_region_open")) { if (updateMeta(region)) { failed = false; } } if (failed || this.server.isStopped() || this.rsServices.isStopping()) { return; } if (!isRegionStillOpening() || !transitionToOpened(region)) { // If we fail to transition to opened, it's because of one of two cases: // (a) we lost our ZK lease // OR (b) someone else opened the region before us // OR (c) someone cancelled the open // In all cases, we try to transition to failed_open to be safe. return; } // We have a znode in the opened state now. We can't really delete it as the master job. // Transitioning to failed open would create a race condition if the master has already // acted the transition to opened. // Cancelling the open is dangerous, because we would have a state where the master thinks // the region is opened while the region is actually closed. It is a dangerous state // to be in. For this reason, from now on, we're not going back. There is a message in the // finally close to let the admin knows where we stand. // Successful region open, and add it to OnlineRegions this.rsServices.addToOnlineRegions(region); openSuccessful = true; // Done! Successful region open LOG.debug("Opened " + regionName + " on " + this.server.getServerName()); } finally { // Do all clean up here if (!openSuccessful) { doCleanUpOnFailedOpen(region, transitionedToOpening); } final Boolean current = this.rsServices.getRegionsInTransitionInRS() .remove(this.regionInfo.getEncodedNameAsBytes()); // Let's check if we have met a race condition on open cancellation.... // A better solution would be to not have any race condition. // this.rsServices.getRegionsInTransitionInRS().remove( // this.regionInfo.getEncodedNameAsBytes(), Boolean.TRUE); // would help, but we would still have a consistency issue to manage with // 1) this.rsServices.addToOnlineRegions(region); // 2) the ZK state. if (openSuccessful) { if (current == null) { // Should NEVER happen, but let's be paranoid. LOG.error("Bad state: we've just opened a region that was NOT in transition. Region=" + regionName); } else if (Boolean.FALSE.equals(current)) { // Can happen, if we're // really unlucky. LOG.error("Race condition: we've finished to open a region, while a close was requested " + " on region=" + regionName + ". It can be a critical error, as a region that" + " should be closed is now opened. Closing it now"); cleanupFailedOpen(region); } } } } private void doCleanUpOnFailedOpen(HRegion region, boolean transitionedToOpening) throws IOException { if (transitionedToOpening) { try { if (region != null) { cleanupFailedOpen(region); } } finally { // Even if cleanupFailed open fails we need to do this transition // See HBASE-7698 tryTransitionFromOpeningToFailedOpen(regionInfo); } } else { // If still transition to OPENING is not done, we need to transition znode // to FAILED_OPEN tryTransitionFromOfflineToFailedOpen(this.rsServices, regionInfo, versionOfOfflineNode); } } /** * Update ZK or META. This can take a while if for example the * hbase:meta is not available -- if server hosting hbase:meta crashed and we are * waiting on it to come back -- so run in a thread and keep updating znode * state meantime so master doesn't timeout our region-in-transition. * Caller must cleanup region if this fails. */ boolean updateMeta(final HRegion r) { if (this.server.isStopped() || this.rsServices.isStopping()) { return false; } // Object we do wait/notify on. Make it boolean. If set, we're done. // Else, wait. final AtomicBoolean signaller = new AtomicBoolean(false); PostOpenDeployTasksThread t = new PostOpenDeployTasksThread(r, this.server, this.rsServices, signaller); t.start(); // Post open deploy task: // meta => update meta location in ZK // other region => update meta // It could fail if ZK/meta is not available and // the update runs out of retries. long now = System.currentTimeMillis(); long lastUpdate = now; boolean tickleOpening = true; while (!signaller.get() && t.isAlive() && !this.server.isStopped() && !this.rsServices.isStopping() && isRegionStillOpening()) { long elapsed = now - lastUpdate; if (elapsed > 120000) { // 2 minutes, no need to tickleOpening too often // Only tickle OPENING if postOpenDeployTasks is taking some time. lastUpdate = now; tickleOpening = tickleOpening("post_open_deploy"); } synchronized (signaller) { try { // Wait for 10 seconds, so that server shutdown // won't take too long if this thread happens to run. signaller.wait(10000); } catch (InterruptedException e) { // Go to the loop check. } } now = System.currentTimeMillis(); } // Is thread still alive? We may have left above loop because server is // stopping or we timed out the edit. Is so, interrupt it. if (t.isAlive()) { if (!signaller.get()) { // Thread still running; interrupt LOG.debug("Interrupting thread " + t); t.interrupt(); } try { t.join(); } catch (InterruptedException ie) { LOG.warn("Interrupted joining " + r.getRegionInfo().getRegionNameAsString(), ie); Thread.currentThread().interrupt(); } } // Was there an exception opening the region? This should trigger on // InterruptedException too. If so, we failed. Even if tickle opening fails // then it is a failure. return ((!Thread.interrupted() && t.getException() == null) && tickleOpening); } /** * Thread to run region post open tasks. Call {@link #getException()} after * the thread finishes to check for exceptions running * {@link RegionServerServices#postOpenDeployTasks( * HRegion, org.apache.hadoop.hbase.catalog.CatalogTracker)} * . */ static class PostOpenDeployTasksThread extends Thread { private Throwable exception = null; private final Server server; private final RegionServerServices services; private final HRegion region; private final AtomicBoolean signaller; PostOpenDeployTasksThread(final HRegion region, final Server server, final RegionServerServices services, final AtomicBoolean signaller) { super("PostOpenDeployTasks:" + region.getRegionInfo().getEncodedName()); this.setDaemon(true); this.server = server; this.services = services; this.region = region; this.signaller = signaller; } public void run() { try { this.services.postOpenDeployTasks(this.region, this.server.getCatalogTracker()); } catch (KeeperException e) { server.abort("Exception running postOpenDeployTasks; region=" + this.region.getRegionInfo().getEncodedName(), e); } catch (Throwable e) { LOG.warn("Exception running postOpenDeployTasks; region=" + this.region.getRegionInfo().getEncodedName(), e); this.exception = e; } // We're done. Set flag then wake up anyone waiting on thread to complete. this.signaller.set(true); synchronized (this.signaller) { this.signaller.notify(); } } /** * @return Null or the run exception; call this method after thread is done. */ Throwable getException() { return this.exception; } } /** * @param r Region we're working on. * @return whether znode is successfully transitioned to OPENED state. * @throws IOException */ boolean transitionToOpened(final HRegion r) throws IOException { boolean result = false; HRegionInfo hri = r.getRegionInfo(); final String name = hri.getRegionNameAsString(); // Finally, Transition ZK node to OPENED try { if (ZKAssign.transitionNodeOpened(this.server.getZooKeeper(), hri, this.server.getServerName(), this.version) == -1) { String warnMsg = "Completed the OPEN of region " + name + " but when transitioning from " + " OPENING to OPENED "; try { String node = ZKAssign.getNodeName(this.server.getZooKeeper(), hri.getEncodedName()); if (ZKUtil.checkExists(this.server.getZooKeeper(), node) < 0) { // if the znode rsServices.abort(warnMsg + "the znode disappeared", null); } else { LOG.warn(warnMsg + "got a version mismatch, someone else clashed; " + "so now unassigning -- closing region on server: " + this.server.getServerName()); } } catch (KeeperException ke) { rsServices.abort(warnMsg, ke); } } else { LOG.debug("Transitioned " + r.getRegionInfo().getEncodedName() + " to OPENED in zk on " + this.server.getServerName()); result = true; } } catch (KeeperException e) { LOG.error("Failed transitioning node " + name + " from OPENING to OPENED -- closing region", e); } return result; } /** * This is not guaranteed to succeed, we just do our best. * @param hri Region we're working on. * @return whether znode is successfully transitioned to FAILED_OPEN state. */ private boolean tryTransitionFromOpeningToFailedOpen(final HRegionInfo hri) { boolean result = false; final String name = hri.getRegionNameAsString(); try { LOG.info("Opening of region " + hri + " failed, transitioning" + " from OPENING to FAILED_OPEN in ZK, expecting version " + this.version); if (ZKAssign.transitionNode(this.server.getZooKeeper(), hri, this.server.getServerName(), EventType.RS_ZK_REGION_OPENING, EventType.RS_ZK_REGION_FAILED_OPEN, this.version) == -1) { LOG.warn("Unable to mark region " + hri + " as FAILED_OPEN. " + "It's likely that the master already timed out this open " + "attempt, and thus another RS already has the region."); } else { result = true; } } catch (KeeperException e) { LOG.error("Failed transitioning node " + name + " from OPENING to FAILED_OPEN", e); } return result; } /** * Try to transition to open. This function is static to make it usable before creating the * handler. * * This is not guaranteed to succeed, we just do our best. * * @param rsServices * @param hri Region we're working on. * @param versionOfOfflineNode version to checked. * @return whether znode is successfully transitioned to FAILED_OPEN state. */ public static boolean tryTransitionFromOfflineToFailedOpen(RegionServerServices rsServices, final HRegionInfo hri, final int versionOfOfflineNode) { boolean result = false; final String name = hri.getRegionNameAsString(); try { LOG.info("Opening of region " + hri + " failed, transitioning" + " from OFFLINE to FAILED_OPEN in ZK, expecting version " + versionOfOfflineNode); if (ZKAssign.transitionNode(rsServices.getZooKeeper(), hri, rsServices.getServerName(), EventType.M_ZK_REGION_OFFLINE, EventType.RS_ZK_REGION_FAILED_OPEN, versionOfOfflineNode) == -1) { LOG.warn("Unable to mark region " + hri + " as FAILED_OPEN. " + "It's likely that the master already timed out this open " + "attempt, and thus another RS already has the region."); } else { result = true; } } catch (KeeperException e) { LOG.error("Failed transitioning node " + name + " from OFFLINE to FAILED_OPEN", e); } return result; } /** * @return Instance of HRegion if successful open else null. */ HRegion openRegion() { HRegion region = null; try { // Instantiate the region. This also periodically tickles our zk OPENING // state so master doesn't timeout this region in transition. region = HRegion.openHRegion(this.regionInfo, this.htd, this.rsServices.getWAL(this.regionInfo), this.server.getConfiguration(), this.rsServices, new CancelableProgressable() { public boolean progress() { // We may lose the znode ownership during the open. Currently its // too hard interrupting ongoing region open. Just let it complete // and check we still have the znode after region open. return tickleOpening("open_region_progress"); } }); } catch (Throwable t) { // We failed open. Our caller will see the 'null' return value // and transition the node back to FAILED_OPEN. If that fails, // we rely on the Timeout Monitor in the master to reassign. LOG.error("Failed open of region=" + this.regionInfo.getRegionNameAsString() + ", starting to roll back the global memstore size.", t); // Decrease the global memstore size. if (this.rsServices != null) { RegionServerAccounting rsAccounting = this.rsServices.getRegionServerAccounting(); if (rsAccounting != null) { rsAccounting.rollbackRegionReplayEditsSize(this.regionInfo.getRegionName()); } } } return region; } void cleanupFailedOpen(final HRegion region) throws IOException { if (region != null) { this.rsServices.removeFromOnlineRegions(region, null); region.close(); } } private boolean isRegionStillOpening() { byte[] encodedName = regionInfo.getEncodedNameAsBytes(); Boolean action = rsServices.getRegionsInTransitionInRS().get(encodedName); return Boolean.TRUE.equals(action); // true means opening for RIT } /** * Transition ZK node from OFFLINE to OPENING. * @param encodedName Name of the znode file (Region encodedName is the znode * name). * @param versionOfOfflineNode - version Of OfflineNode that needs to be compared * before changing the node's state from OFFLINE * @return True if successful transition. */ boolean transitionZookeeperOfflineToOpening(final String encodedName, int versionOfOfflineNode) { // TODO: should also handle transition from CLOSED? try { // Initialize the znode version. this.version = ZKAssign.transitionNode(server.getZooKeeper(), regionInfo, server.getServerName(), EventType.M_ZK_REGION_OFFLINE, EventType.RS_ZK_REGION_OPENING, versionOfOfflineNode); } catch (KeeperException e) { LOG.error("Error transition from OFFLINE to OPENING for region=" + encodedName, e); this.version = -1; return false; } boolean b = isGoodVersion(); if (!b) { LOG.warn("Failed transition from OFFLINE to OPENING for region=" + encodedName); } return b; } /** * Update our OPENING state in zookeeper. * Do this so master doesn't timeout this region-in-transition. * @param context Some context to add to logs if failure * @return True if successful transition. */ boolean tickleOpening(final String context) { if (!isRegionStillOpening()) { LOG.warn("Open region aborted since it isn't opening any more"); return false; } // If previous checks failed... do not try again. if (!isGoodVersion()) return false; String encodedName = this.regionInfo.getEncodedName(); try { this.version = ZKAssign.confirmNodeOpening(server.getZooKeeper(), this.regionInfo, this.server.getServerName(), this.version); } catch (KeeperException e) { server.abort("Exception refreshing OPENING; region=" + encodedName + ", context=" + context, e); this.version = -1; return false; } boolean b = isGoodVersion(); if (!b) { LOG.warn("Failed refreshing OPENING; region=" + encodedName + ", context=" + context); } return b; } private boolean isGoodVersion() { return this.version != -1; } }