From 5848710aa707c41d1c3ecaa1442859ab2b9f878c Mon Sep 17 00:00:00 2001 From: Jonathan M Hsieh Date: Thu, 7 Aug 2014 13:27:40 -0700 Subject: [PATCH] HBASE-6626 Add a chapter on HDFS in the troubleshooting section of the HBase reference guide (Misty Stanley-Jones) --- src/main/docbkx/troubleshooting.xml | 209 ++++++++++++++++++++++++++++ 1 file changed, 209 insertions(+) diff --git a/src/main/docbkx/troubleshooting.xml b/src/main/docbkx/troubleshooting.xml index 01ad5dc9e07..4cd4a9e379c 100644 --- a/src/main/docbkx/troubleshooting.xml +++ b/src/main/docbkx/troubleshooting.xml @@ -1267,6 +1267,215 @@ sv4r6s38: at org.apache.hadoop.security.UserGroupInformation.ensureInitial +
+ HBase and HDFS + General configuration guidance for Apache HDFS is out of the scope of this guide. Refer to + the documentation available at http://hadoop.apache.org/ for extensive + information about configuring HDFS. This section deals with HDFS in terms of HBase. + + In most cases, HBase stores its data in Apache HDFS. This includes the HFiles containing + the data, as well as the write-ahead logs (WALs) which store data before it is written to the + HFiles and protect against RegionServer crashes. HDFS provides reliability and protection to + data in HBase because it is distributed. To operate with the most efficiency, HBase needs data + to be available locally. Therefore, it is a good practice to run an HDFS datanode on each + RegionServer. + + Important Information and Guidelines for HBase and HDFS + + HBase is a client of HDFS. + + HBase is an HDFS client, using the HDFS DFSClient class, and references + to this class appear in HBase logs with other HDFS client log messages. + + + + Configuration is necessary in multiple places. + + Some HDFS configurations relating to HBase need to be done at the HDFS (server) side. + Others must be done within HBase (at the client side). Other settings need + to be set at both the server and client side. + + + + + Write errors which affect HBase may be logged in the HDFS logs rather than HBase logs. + + When writing, HDFS pipelines communications from one datanode to another. HBase + communicates to both the HDFS namenode and datanode, using the HDFS client classes. + Communication problems between datanodes are logged in the HDFS logs, not the HBase + logs. + HDFS writes are always local when possible. HBase RegionServers should not + experience many write errors, because they write the local datanode. If the datanode + cannot replicate the blocks, the errors are logged in HDFS, not in the HBase + RegionServer logs. + + + + HBase communicates with HDFS using two different ports. + + HBase communicates with datanodes using the ipc.Client interface and + the DataNode class. References to these will appear in HBase logs. Each of + these communication channels use a different port (50010 and 50020 by default). The + ports are configured in the HDFS configuration, via the + dfs.datanode.address and dfs.datanode.ipc.address + parameters. + + + + Errors may be logged in HBase, HDFS, or both. + + When troubleshooting HDFS issues in HBase, check logs in both places for errors. + + + + HDFS takes a while to mark a node as dead. You can configure HDFS to avoid using stale + datanodes. + + By default, HDFS does not mark a node as dead until it is unreachable for 630 + seconds. In Hadoop 1.1 and Hadoop 2.x, this can be alleviated by enabling checks for + stale datanodes, though this check is disabled by default. You can enable the check for + reads and writes separately, via dfs.namenode.avoid.read.stale.datanode and + dfs.namenode.avoid.write.stale.datanode settings. A stale datanode is one + that has not been reachable for dfs.namenode.stale.datanode.interval + (default is 30 seconds). Stale datanodes are avoided, and marked as the last possible + target for a read or write operation. For configuration details, see the HDFS + documentation. + + + + Settings for HDFS retries and timeouts are important to HBase. + + You can configure settings for various retries and timeouts. Always refer to the + HDFS documentation for current recommendations and defaults. Some of the settings + important to HBase are listed here. Defaults are current as of Hadoop 2.3. Check the + Hadoop documentation for the most current values and recommendations. + + Retries + + ipc.client.connect.max.retries (default: 10) + + The number of times a client will attempt to establish a connection with the + server. This value sometimes needs to be increased. You can specify different + setting for the maximum number of retries if a timeout occurs. For SASL + connections, the number of retries is hard-coded at 15 and cannot be + configured. + + + ipc.client.connect.max.retries.on.timeouts (default: 45) + The number of times a client will attempt to establish a connection + with the server in the event of a timeout. If some retries are due to timeouts and + some are due to other reasons, this counter is added to + ipc.client.connect.max.retries, so the maximum number of retries for + all reasons could be the combined value. + + + dfs.client.block.write.retries (default: 3) + How many times the client attempts to write to the datanode. After the + number of retries is reached, the client reconnects to the namenode to get a new + location of a datanode. You can try increasing this value. + + + + HDFS Heartbeats + HDFS heartbeats are entirely on the HDFS side, between the namenode and datanodes. + + dfs.heartbeat.interval (default: 3) + The interval at which a node heartbeats. + + + dfs.namenode.heartbeat.recheck-interval (default: 300000) + + The interval of time between heartbeat checks. The total time before a node is + marked as stale is determined by the following formula, which works out to 10 + minutes and 30 seconds: + 2 * (dfs.namenode.heartbeat.recheck-interval) + 10 * 1000 * (dfs.heartbeat.interval) + + + + dfs.namenode.stale.datanode.interval (default: 3000) + + How long (in milliseconds) a node can go without a heartbeat before it is + determined to be stale, if the other options to do with stale datanodes are + configured (off by default). + + + + + + + Connection Timeouts + Connection timeouts occur between the client (HBASE) and the HDFS datanode. They may + occur when establishing a connection, attempting to read, or attempting to write. The two + settings below are used in combination, and affect connections between the DFSClient and the + datanode, the ipc.cClient and the datanode, and communication between two datanodes. + + dfs.client.socket-timeout (default: 60000) + + The amount of time before a client connection times out when establishing a + connection or reading. The value is expressed in milliseconds, so the default is 60 + seconds. + + + + dfs.datanode.socket.write.timeout (default: 480000) + + The amount of time before a write operation times out. The default is 8 + minutes, expressed as milliseconds. + + + + + Typical Error Logs + The following types of errors are often seen in the logs. + + INFO HDFS.DFSClient: Failed to connect to /xxx50010, add to deadNodes and + continue java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel + to be ready for connect. ch : java.nio.channels.SocketChannel[connection-pending + remote=/region-server-1:50010] + + All datanodes for a block are dead, and recovery is not possible. Here is the + sequence of events that leads to this error: + + + The client attempts to connect to a dead datanode. + + + The connection fails, so the client moves down the list of datanodes and tries + the next one. It also fails. + + + When the client exhausts its entire list, it sleeps for 3 seconds and requests a + new list. It is very likely to receive the exact same list as before, in which case + the error occurs again. + + + + + + INFO org.apache.hadoop.HDFS.DFSClient: Exception in createBlockOutputStream + java.net.SocketTimeoutException: 69000 millis timeout while waiting for channel to be + ready for connect. ch : java.nio.channels.SocketChannel[connection-pending remote=/ + xxx:50010] + + This type of error indicates a write issue. In this case, the master wants to split + the log. It does not have a local datanode so it tries to connect to a remote datanode, + but the datanode is dead. + In this situation, there will be three retries (by default). If all retries fail, a + message like the following is logged: + +WARN HDFS.DFSClient: DataStreamer Exception: java.io.IOException: Unable to create new block + + If the operation was an attempt to split the log, the following type of message may + also appear: + +FATAL wal.HLogSplitter: WriterThread-xxx Got while writing log entry to log + + + + +
+
Running unit or integration tests