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| |
| <h1>Apache Kudu (incubating) Troubleshooting</h1> |
| <div class="sect1"> |
| <h2 id="_issues_starting_the_master_or_tablet_server"><a class="link" href="#_issues_starting_the_master_or_tablet_server">Issues starting the Master or Tablet Server</a></h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="req_hole_punching"><a class="link" href="#req_hole_punching">Errors During Hole Punching Test</a></h3> |
| <div class="paragraph"> |
| <p>Kudu requires hole punching capabilities in order to be efficient. Hole punching support |
| depends upon your operation system kernel version and local filesystem implementation.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>RHEL or CentOS 6.4 or later, patched to kernel version of 2.6.32-358 or later. |
| Unpatched RHEL or CentOS 6.4 does not include a kernel with support for hole punching.</p> |
| </li> |
| <li> |
| <p>Ubuntu 14.04 includes version 3.13 of the Linux kernel, which supports hole punching.</p> |
| </li> |
| <li> |
| <p>Newer versions of the EXT4 or XFS file systems support hole punching, but EXT3 does |
| not. Older versions of XFS that do not support hole punching return a <code>EOPNOTSUPP</code> |
| (operation not supported) error. Older versions of either EXT4 or XFS that do |
| not support hole punching cause Kudu to emit an error message such as the following |
| and to fail to start:</p> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>Error during hole punch test. The log block manager requires a |
| filesystem with hole punching support such as ext4 or xfs. On el6, |
| kernel version 2.6.32-358 or newer is required. To run without hole |
| punching (at the cost of some efficiency and scalability), reconfigure |
| Kudu with --block_manager=file. Refer to the Kudu documentation for more |
| details. Raw error message follows.</pre> |
| </div> |
| </div> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Without hole punching support, the log block manager is unsafe to use. It won’t |
| ever delete blocks, and will consume ever more space on disk.</p> |
| </div> |
| <div class="paragraph"> |
| <p>If you can’t use hole punching in your environment, you can still |
| try Kudu. Enable the file block manager instead of the log block manager by |
| adding the <code>--block_manager=file</code> flag to the commands you use to start the master |
| and tablet servers. The file block manager does not scale as well as the log block |
| manager.</p> |
| </div> |
| <div class="admonitionblock warning"> |
| <table> |
| <tr> |
| <td class="icon"> |
| <i class="fa icon-warning" title="Warning"></i> |
| </td> |
| <td class="content"> |
| The file block manager is known to scale and perform poorly, and should |
| only be used for small-scale evaluation and development. |
| </td> |
| </tr> |
| </table> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="ntp"><a class="link" href="#ntp">NTP clock synchronization</a></h3> |
| <div class="paragraph"> |
| <p>For the master and tablet server daemons, the server’s clock must be synchronized using NTP. |
| In addition, the <strong>maximum clock error</strong> (not to be mistaken with the estimated error) |
| be below a configurable threshold. The default value is 10 seconds, but it can be set with the flag |
| <code>--max_clock_sync_error_usec</code>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>If NTP is not installed, or if the clock is reported as unsynchronized, Kudu will not |
| start, and will emit a message such as:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>F0924 20:24:36.336809 14550 hybrid_clock.cc:191 Couldn't get the current time: Clock unsynchronized. Status: Service unavailable: Error reading clock. Clock considered unsynchronized.</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>If NTP is installed and synchronized, but the maximum clock error is too high, |
| the user will see a message such as:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>Sep 17, 8:13:09.873 PM FATAL hybrid_clock.cc:196 Couldn't get the current time: Clock synchronized, but error: 11130000, is past the maximum allowable error: 10000000</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>or</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>Sep 17, 8:32:31.135 PM FATAL tablet_server_main.cc:38 Check failed: _s.ok() Bad status: Service unavailable: Cannot initialize clock: Cannot initialize HybridClock. Clock synchronized but error was too high (11711000 us).</pre> |
| </div> |
| </div> |
| <div class="admonitionblock tip"> |
| <table> |
| <tr> |
| <td class="icon"> |
| <i class="fa icon-tip" title="Tip"></i> |
| </td> |
| <td class="content"> |
| If NTP is installed the user can monitor the synchronization status by running |
| <code>ntptime</code>. The relevant value is what is reported for <code>maximum error</code>. |
| </td> |
| </tr> |
| </table> |
| </div> |
| <div class="paragraph"> |
| <p>To install NTP, use the appropriate command for your operating system:</p> |
| </div> |
| <table class="tableblock frame-all grid-all spread"> |
| <colgroup> |
| <col style="width: 50%;"> |
| <col style="width: 50%;"> |
| </colgroup> |
| <thead> |
| <tr> |
| <th class="tableblock halign-left valign-top">OS</th> |
| <th class="tableblock halign-left valign-top">Command</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Debian/Ubuntu</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><code>sudo apt-get install ntp</code></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">RHEL/CentOS</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><code>sudo yum install ntp</code></p></td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="paragraph"> |
| <p>If NTP is installed but not running, start it using one of these commands:</p> |
| </div> |
| <table class="tableblock frame-all grid-all spread"> |
| <colgroup> |
| <col style="width: 50%;"> |
| <col style="width: 50%;"> |
| </colgroup> |
| <thead> |
| <tr> |
| <th class="tableblock halign-left valign-top">OS</th> |
| <th class="tableblock halign-left valign-top">Command</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Debian/Ubuntu</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><code>sudo service ntp restart</code></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">RHEL/CentOS</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><code>sudo /etc/init.d/ntpd restart</code></p></td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="admonitionblock tip"> |
| <table> |
| <tr> |
| <td class="icon"> |
| <i class="fa icon-tip" title="Tip"></i> |
| </td> |
| <td class="content"> |
| NTP requires a network connection and may take a few minutes to synchronize the clock. |
| In some cases a spotty network connection may make NTP report the clock as unsynchronized. |
| A common, though temporary, workaround for this is to restart NTP with one of the commands above. |
| </td> |
| </tr> |
| </table> |
| </div> |
| <div class="paragraph"> |
| <p>If the clock is being reported as synchronized by NTP, but the maximum error is too high, |
| the user can increase the threshold to a higher value by setting the above |
| mentioned flag. For example to increase the possible maximum error to |
| 20 seconds the flag should be set like: <code>--max_clock_sync_error_usec=20000000</code></p> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_troubleshooting_performance_issues"><a class="link" href="#_troubleshooting_performance_issues">Troubleshooting Performance Issues</a></h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="kudu_tracing"><a class="link" href="#kudu_tracing">Kudu Tracing</a></h3> |
| <div class="paragraph"> |
| <p>The <code>kudu-master</code> and <code>kudu-tserver</code> daemons include built-in tracing support |
| based on the open source |
| <a href="https://www.chromium.org/developers/how-tos/trace-event-profiling-tool">Chromium Tracing</a> |
| framework. You can use tracing to help diagnose latency issues or other problems |
| on Kudu servers.</p> |
| </div> |
| <div class="sect3"> |
| <h4 id="_accessing_the_tracing_interface"><a class="link" href="#_accessing_the_tracing_interface">Accessing the tracing interface</a></h4> |
| <div class="paragraph"> |
| <p>The tracing interface is accessed via a web browser as part of the |
| embedded web server in each of the Kudu daemons.</p> |
| </div> |
| <table class="tableblock frame-all grid-all spread"> |
| <caption class="title">Table 1. Tracing Interface URLs</caption> |
| <colgroup> |
| <col style="width: 50%;"> |
| <col style="width: 50%;"> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Daemon</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">URL</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Tablet Server</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="http://tablet-server-1.example.com:8050/tracing.html" class="bare">http://tablet-server-1.example.com:8050/tracing.html</a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Master</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="http://master-1.example.com:8051/tracing.html" class="bare">http://master-1.example.com:8051/tracing.html</a></p></td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="admonitionblock warning"> |
| <table> |
| <tr> |
| <td class="icon"> |
| <i class="fa icon-warning" title="Warning"></i> |
| </td> |
| <td class="content"> |
| The tracing interface is known to work in recent versions of Google Chrome. |
| Other browsers may not work as expected. |
| </td> |
| </tr> |
| </table> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_collecting_a_trace"><a class="link" href="#_collecting_a_trace">Collecting a trace</a></h4> |
| <div class="paragraph"> |
| <p>After navigating to the tracing interface, click the <strong>Record</strong> button on the top left corner |
| of the screen. When beginning to diagnose a problem, start by selecting all categories. |
| Click <strong>Record</strong> to begin recording a trace.</p> |
| </div> |
| <div class="paragraph"> |
| <p>During the trace collection, events are collected into an in-memory ring buffer. |
| This ring buffer is fixed in size, so it will eventually fill up to 100%. However, new events |
| are still being collected while older events are being removed. While recording the trace, |
| trigger the behavior or workload you are interested in exploring.</p> |
| </div> |
| <div class="paragraph"> |
| <p>After collecting for several seconds, click <strong>Stop</strong>. The collected trace will be |
| downloaded and displayed. Use the <strong>?</strong> key to display help text about using the tracing |
| interface to explore the trace.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_saving_a_trace"><a class="link" href="#_saving_a_trace">Saving a trace</a></h4> |
| <div class="paragraph"> |
| <p>You can save collected traces as JSON files for later analysis by clicking <strong>Save</strong> |
| after collecting the trace. To load and analyze a saved JSON file, click <strong>Load</strong> |
| and choose the file.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_rpc_timeout_traces"><a class="link" href="#_rpc_timeout_traces">RPC Timeout Traces</a></h3> |
| <div class="paragraph"> |
| <p>If client applications are experiencing RPC timeouts, the Kudu tablet server |
| <code>WARNING</code> level logs should contain a log entry which includes an RPC-level trace. For example:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>W0922 00:56:52.313848 10858 inbound_call.cc:193] Call kudu.consensus.ConsensusService.UpdateConsensus |
| from 192.168.1.102:43499 (request call id 3555909) took 1464ms (client timeout 1000). |
| W0922 00:56:52.314888 10858 inbound_call.cc:197] Trace: |
| 0922 00:56:50.849505 (+ 0us) service_pool.cc:97] Inserting onto call queue |
| 0922 00:56:50.849527 (+ 22us) service_pool.cc:158] Handling call |
| 0922 00:56:50.849574 (+ 47us) raft_consensus.cc:1008] Updating replica for 2 ops |
| 0922 00:56:50.849628 (+ 54us) raft_consensus.cc:1050] Early marking committed up to term: 8 index: 880241 |
| 0922 00:56:50.849968 (+ 340us) raft_consensus.cc:1056] Triggering prepare for 2 ops |
| 0922 00:56:50.850119 (+ 151us) log.cc:420] Serialized 1555 byte log entry |
| 0922 00:56:50.850213 (+ 94us) raft_consensus.cc:1131] Marking committed up to term: 8 index: 880241 |
| 0922 00:56:50.850218 (+ 5us) raft_consensus.cc:1148] Updating last received op as term: 8 index: 880243 |
| 0922 00:56:50.850219 (+ 1us) raft_consensus.cc:1195] Filling consensus response to leader. |
| 0922 00:56:50.850221 (+ 2us) raft_consensus.cc:1169] Waiting on the replicates to finish logging |
| 0922 00:56:52.313763 (+1463542us) raft_consensus.cc:1182] finished |
| 0922 00:56:52.313764 (+ 1us) raft_consensus.cc:1190] UpdateReplicas() finished |
| 0922 00:56:52.313788 (+ 24us) inbound_call.cc:114] Queueing success response</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>These traces can give an indication of which part of the request was slow. Please |
| include them in bug reports related to RPC latency outliers.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_kernel_stack_watchdog_traces"><a class="link" href="#_kernel_stack_watchdog_traces">Kernel Stack Watchdog Traces</a></h3> |
| <div class="paragraph"> |
| <p>Each Kudu server process has a background thread called the Stack Watchdog, which |
| monitors the other threads in the server in case they have blocked for |
| longer-than-expected periods of time. These traces can indicate operating system issues |
| or bottlenecked storage.</p> |
| </div> |
| <div class="paragraph"> |
| <p>When the watchdog thread identifies a case of thread blockage, it logs an entry |
| in the <code>WARNING</code> log like the following:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre>W0921 23:51:54.306350 10912 kernel_stack_watchdog.cc:111] Thread 10937 stuck at /data/kudu/consensus/log.cc:505 for 537ms: |
| Kernel stack: |
| [<ffffffffa00b209d>] do_get_write_access+0x29d/0x520 [jbd2] |
| [<ffffffffa00b2471>] jbd2_journal_get_write_access+0x31/0x50 [jbd2] |
| [<ffffffffa00fe6d8>] __ext4_journal_get_write_access+0x38/0x80 [ext4] |
| [<ffffffffa00d9b23>] ext4_reserve_inode_write+0x73/0xa0 [ext4] |
| [<ffffffffa00d9b9c>] ext4_mark_inode_dirty+0x4c/0x1d0 [ext4] |
| [<ffffffffa00d9e90>] ext4_dirty_inode+0x40/0x60 [ext4] |
| [<ffffffff811ac48b>] __mark_inode_dirty+0x3b/0x160 |
| [<ffffffff8119c742>] file_update_time+0xf2/0x170 |
| [<ffffffff8111c1e0>] __generic_file_aio_write+0x230/0x490 |
| [<ffffffff8111c4c8>] generic_file_aio_write+0x88/0x100 |
| [<ffffffffa00d3fb1>] ext4_file_write+0x61/0x1e0 [ext4] |
| [<ffffffff81180f5b>] do_sync_readv_writev+0xfb/0x140 |
| [<ffffffff81181ee6>] do_readv_writev+0xd6/0x1f0 |
| [<ffffffff81182046>] vfs_writev+0x46/0x60 |
| [<ffffffff81182102>] sys_pwritev+0xa2/0xc0 |
| [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b |
| [<ffffffffffffffff>] 0xffffffffffffffff |
| |
| User stack: |
| @ 0x3a1ace10c4 (unknown) |
| @ 0x1262103 (unknown) |
| @ 0x12622d4 (unknown) |
| @ 0x12603df (unknown) |
| @ 0x8e7bfb (unknown) |
| @ 0x8f478b (unknown) |
| @ 0x8f55db (unknown) |
| @ 0x12a7b6f (unknown) |
| @ 0x3a1b007851 (unknown) |
| @ 0x3a1ace894d (unknown) |
| @ (nil) (unknown)</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>These traces can be useful for diagnosing root-cause latency issues when they are caused by systems |
| below Kudu, such as disk controllers or file systems.</p> |
| </div> |
| </div> |
| </div> |
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