impala/docs/topics/impala_logging.xml

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="logging">

  <title>Using Impala Logging</title>
  <titlealts audience="PDF"><navtitle>Logging</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Logs"/>
      <data name="Category" value="Troubleshooting"/>
      <data name="Category" value="Administrators"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      The Impala logs record information about:
    </p>

    <ul>
      <li>
        Any errors Impala encountered. If Impala experienced a serious error during startup, you must diagnose and
        troubleshoot that problem before you can do anything further with Impala.
      </li>

      <li>
        How Impala is configured.
      </li>

      <li>
        Jobs Impala has completed.
      </li>
    </ul>

    <note>
      <p>
        Formerly, the logs contained the query profile for each query, showing low-level details of how the work is
        distributed among nodes and how intermediate and final results are transmitted across the network. To save
        space, those query profiles are now stored in zlib-compressed files in
        <filepath>/var/log/impala/profiles</filepath>. You can access them through the Impala web user interface.
        For example, at <codeph>http://<varname>impalad-node-hostname</varname>:25000/queries</codeph>, each query
        is followed by a <codeph>Profile</codeph> link leading to a page showing extensive analytical data for the
        query execution.
      </p>

      <p rev="1.1.1">
        The auditing feature introduced in Impala 1.1.1 produces a separate set of audit log files when
        enabled. See <xref href="impala_auditing.xml#auditing"/> for details.
      </p>

      <p rev="2.2.0">
        The lineage feature introduced in Impala 2.2.0 produces a separate lineage log file when
        enabled. See <xref href="impala_lineage.xml#lineage"/> for details.
      </p>
    </note>

    <p outputclass="toc inpage"/>

  </conbody>

  <concept id="logs_details">

    <title>Locations and Names of Impala Log Files</title>

    <conbody>

      <ul>
        <li>
          By default, the log files are under the directory <filepath>/var/log/impala</filepath>.
<!-- TK: split this task out and state CM and non-CM ways. -->
          To change log file locations, modify the defaults file described in
          <xref href="impala_processes.xml#processes"/>.
        </li>

        <li>
          The significant files for the <codeph>impalad</codeph> process are <filepath>impalad.INFO</filepath>,
          <filepath>impalad.WARNING</filepath>, and <filepath>impalad.ERROR</filepath>. You might also see a file
          <filepath>impalad.FATAL</filepath>, although this is only present in rare conditions.
        </li>

        <li>
          The significant files for the <codeph>statestored</codeph> process are
          <filepath>statestored.INFO</filepath>, <filepath>statestored.WARNING</filepath>, and
          <filepath>statestored.ERROR</filepath>. You might also see a file <filepath>statestored.FATAL</filepath>,
          although this is only present in rare conditions.
        </li>

        <li rev="1.2">
          The significant files for the <codeph>catalogd</codeph> process are <filepath>catalogd.INFO</filepath>,
          <filepath>catalogd.WARNING</filepath>, and <filepath>catalogd.ERROR</filepath>. You might also see a file
          <filepath>catalogd.FATAL</filepath>, although this is only present in rare conditions.
        </li>

        <li>
          Examine the <codeph>.INFO</codeph> files to see configuration settings for the processes.
        </li>

        <li>
          Examine the <codeph>.WARNING</codeph> files to see all kinds of problem information, including such
          things as suboptimal settings and also serious runtime errors.
        </li>

        <li>
          Examine the <codeph>.ERROR</codeph> and/or <codeph>.FATAL</codeph> files to see only the most serious
          errors, if the processes crash, or queries fail to complete. These messages are also in the
          <codeph>.WARNING</codeph> file.
        </li>

        <li>
          A new set of log files is produced each time the associated daemon is restarted. These log files have
          long names including a timestamp. The <codeph>.INFO</codeph>, <codeph>.WARNING</codeph>, and
          <codeph>.ERROR</codeph> files are physically represented as symbolic links to the latest applicable log
          files.
        </li>

        <li>
          The init script for the <codeph>impala-server</codeph> service also produces a consolidated log file
          <codeph>/var/logs/impalad/impala-server.log</codeph>, with all the same information as the
          corresponding<codeph>.INFO</codeph>, <codeph>.WARNING</codeph>, and <codeph>.ERROR</codeph> files.
        </li>

        <li>
          The init script for the <codeph>impala-state-store</codeph> service also produces a consolidated log file
          <codeph>/var/logs/impalad/impala-state-store.log</codeph>, with all the same information as the
          corresponding<codeph>.INFO</codeph>, <codeph>.WARNING</codeph>, and <codeph>.ERROR</codeph> files.
        </li>
      </ul>

      <p>
        Impala stores information using the <codeph>glog_v</codeph> logging system. You will see some messages
        referring to C++ file names. Logging is affected by:
      </p>

      <ul>
        <li>
          The <codeph>GLOG_v</codeph> environment variable specifies which types of messages are logged. See
          <xref href="#log_levels"/> for details.
        </li>

        <li>
          The <codeph>-logbuflevel</codeph> startup flag for the <cmdname>impalad</cmdname> daemon specifies how
          often the log information is written to disk. The default is 0, meaning that the log is immediately
          flushed to disk when Impala outputs an important messages such as a warning or an error, but less
          important messages such as informational ones are buffered in memory rather than being flushed to disk
          immediately.
        </li>

        <li audience="Cloudera">
          Cloudera Manager has an Impala configuration setting that sets the <codeph>-logbuflevel</codeph> startup
          option.
        </li>
      </ul>

    </conbody>

  </concept>

  <concept id="logs_cm_noncm">

    <title>Managing Impala Logs</title>
  <prolog>
    <metadata>
      <data name="Category" value="Administrators"/>
      <data name="Category" value="Cloudera Manager"/>
    </metadata>
  </prolog>

    <conbody>

      <p rev="upstream" audience="Cloudera"><!-- Whole paragraph can probably go. -->
        <ph rev="upstream">Cloudera</ph> recommends installing Impala through the Cloudera Manager administration interface. To assist with
        troubleshooting, Cloudera Manager collects front-end and back-end logs together into a single view, and let
        you do a search across log data for all the managed nodes rather than examining the logs on each node
        separately. If you installed Impala using Cloudera Manager, refer to the topics on Monitoring Services
        (<xref href="http://www.cloudera.com/documentation/enterprise/latest/topics/cm_dg_service_monitoring.html" scope="external" format="html">CDH 5</xref>)
        or Logs (<xref href="http://www.cloudera.com/documentation/enterprise/latest/topics/cm_dg_logs.html" scope="external" format="html">CDH 5</xref>).
      </p>

      <p>
        If you are using Impala in an environment not managed by Cloudera Manager, review Impala log files on each
        host, when you have traced an issue back to a specific system.
      </p>

    </conbody>

  </concept>

  <concept id="logs_rotate">

    <title>Rotating Impala Logs</title>
  <prolog>
    <metadata>
      <data name="Category" value="Disk Storage"/>
    </metadata>
  </prolog>

    <conbody>

      <p>
        Impala periodically switches the physical files representing the current log files, after which it is safe
        to remove the old files if they are no longer needed.
      </p>

      <p>
        Impala can automatically remove older unneeded log files, a feature known as <term>log rotation</term>.
<!-- Another instance of the text also used in impala_new_features.xml
             and impala_fixed_issues.xml. (Just took out the word "new"
             and added the reference to the starting release.)
             At this point, a conref is definitely in the cards. -->
      </p>

      <p>
        In Impala 2.2 and higher, the <codeph>-max_log_files</codeph> configuration option specifies how many log
        files to keep at each severity level. You can specify an appropriate setting for each Impala-related daemon
        (<cmdname>impalad</cmdname>, <cmdname>statestored</cmdname>, and <cmdname>catalogd</cmdname>). The default
        value is 10, meaning that Impala preserves the latest 10 log files for each severity level
        (<codeph>INFO</codeph>, <codeph>WARNING</codeph>, <codeph>ERROR</codeph>, and <codeph>FATAL</codeph>).
        Impala checks to see if any old logs need to be removed based on the interval specified in the
        <codeph>logbufsecs</codeph> setting, every 5 seconds by default.
      </p>

<!-- This extra detail only appears here. Consider if it's worth including it
           in the conref so people don't need to follow a link just for a couple of
           minor factoids. -->

      <p>
        A value of 0 preserves all log files, in which case you would set up set up manual log rotation using your
        Linux tool or technique of choice. A value of 1 preserves only the very latest log file.
      </p>

      <p audience="Cloudera">
        To set up log rotation on a system managed by Cloudera Manager 5.4.0 and higher, search for the
        <codeph>max_log_files</codeph> option name and set the appropriate value for the <userinput>Maximum Log
        Files</userinput> field for each Impala configuration category (Impala, Catalog Server, and StateStore).
        Then restart the Impala service. In earlier Cloudera Manager releases, specify the
        <codeph>-max_log_files=<varname>maximum</varname></codeph> option in the <uicontrol>Command Line Argument
        Advanced Configuration Snippet (Safety Valve)</uicontrol> field for each Impala configuration category.
      </p>

    </conbody>

  </concept>

  <concept id="logs_debug">

    <title>Reviewing Impala Logs</title>

    <conbody>

      <p>
        By default, the Impala log is stored at <codeph>/var/logs/impalad/</codeph>. The most comprehensive log,
        showing informational, warning, and error messages, is in the file name <filepath>impalad.INFO</filepath>.
        View log file contents by using the web interface or by examining the contents of the log file. (When you
        examine the logs through the file system, you can troubleshoot problems by reading the
        <filepath>impalad.WARNING</filepath> and/or <filepath>impalad.ERROR</filepath> files, which contain the
        subsets of messages indicating potential problems.)
      </p>

      <p>
        On a machine named <codeph>impala.example.com</codeph> with default settings, you could view the Impala
        logs on that machine by using a browser to access <codeph>http://impala.example.com:25000/logs</codeph>.
      </p>

      <note>
        <p>
          The web interface limits the amount of logging information displayed. To view every log entry, access the
          log files directly through the file system.
        </p>
      </note>

      <p>
        You can view the contents of the <codeph>impalad.INFO</codeph> log file in the file system. With the
        default configuration settings, the start of the log file appears as follows:
      </p>

<codeblock>[user@example impalad]$ pwd
/var/log/impalad
[user@example impalad]$ more impalad.INFO
Log file created at: 2013/01/07 08:42:12
Running on machine: impala.example.com
Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msg
I0107 08:42:12.292155 14876 daemon.cc:34] impalad version 0.4 RELEASE (build 9d7fadca0461ab40b9e9df8cdb47107ec6b27cff)
Built on Fri, 21 Dec 2012 12:55:19 PST
I0107 08:42:12.292484 14876 daemon.cc:35] Using hostname: impala.example.com
I0107 08:42:12.292706 14876 logging.cc:76] Flags (see also /varz are on debug webserver):
--dump_ir=false
--module_output=
--be_port=22000
--classpath=
--hostname=impala.example.com</codeblock>

      <note>
        The preceding example shows only a small part of the log file. Impala log files are often several megabytes
        in size.
      </note>

    </conbody>

  </concept>

  <concept id="log_format">

    <title>Understanding Impala Log Contents</title>

    <conbody>

      <p>
        The logs store information about Impala startup options. This information appears once for each time Impala
        is started and may include:
      </p>

      <ul>
        <li>
          Machine name.
        </li>

        <li>
          Impala version number.
        </li>

        <li>
          Flags used to start Impala.
        </li>

        <li>
          CPU information.
        </li>

        <li>
          The number of available disks.
        </li>
      </ul>

      <p>
        There is information about each job Impala has run. Because each Impala job creates an additional set of
        data about queries, the amount of job specific data may be very large. Logs may contained detailed
        information on jobs. These detailed log entries may include:
      </p>

      <ul>
        <li>
          The composition of the query.
        </li>

        <li>
          The degree of data locality.
        </li>

        <li>
          Statistics on data throughput and response times.
        </li>
      </ul>

    </conbody>

  </concept>

  <concept id="log_levels">

    <title>Setting Logging Levels</title>

    <conbody>

      <p>
        Impala uses the GLOG system, which supports three logging levels. You can adjust the logging levels using
        the Cloudera Manager Admin Console. You can adjust logging levels without going through the Cloudera
        Manager Admin Console by exporting variable settings. To change logging settings manually, use a command
        similar to the following on each node before starting <codeph>impalad</codeph>:
      </p>

<codeblock>export GLOG_v=1</codeblock>

      <note>
        For performance reasons, Cloudera highly recommends not enabling the most verbose logging level of 3.
      </note>

      <p>
        For more information on how to configure GLOG, including how to set variable logging levels for different
        system components, see
        <xref href="http://google-glog.googlecode.com/svn/trunk/doc/glog.html" scope="external" format="html">How
        To Use Google Logging Library (glog)</xref>.
      </p>

      <section id="loglevels_details">

        <title>Understanding What is Logged at Different Logging Levels</title>

        <p>
          As logging levels increase, the categories of information logged are cumulative. For example, GLOG_v=2
          records everything GLOG_v=1 records, as well as additional information.
        </p>

        <p>
          Increasing logging levels imposes performance overhead and increases log size. <ph rev="upstream">Cloudera</ph> recommends using
          GLOG_v=1 for most cases: this level has minimal performance impact but still captures useful
          troubleshooting information.
        </p>

        <p>
          Additional information logged at each level is as follows:
        </p>

        <ul>
          <li>
            GLOG_v=1 - The default level. Logs information about each connection and query that is initiated to an
            <codeph>impalad</codeph> instance, including runtime profiles.
          </li>

          <li>
            GLOG_v=2 - Everything from the previous level plus information for each RPC initiated. This level also
            records query execution progress information, including details on each file that is read.
          </li>

          <li>
            GLOG_v=3 - Everything from the previous level plus logging of every row that is read. This level is
            only applicable for the most serious troubleshooting and tuning scenarios, because it can produce
            exceptionally large and detailed log files, potentially leading to its own set of performance and
            capacity problems.
          </li>
        </ul>

      </section>

    </conbody>

  </concept>

  <concept id="redaction" rev="2.2.0">

    <title>Redacting Sensitive Information from Impala Log Files</title>
    <prolog>
      <metadata>
        <data name="Category" value="Redaction"/>
      </metadata>
    </prolog>

    <conbody>

      <p>
        <indexterm audience="Cloudera">redaction</indexterm>
        <term>Log redaction</term> is a security feature that prevents sensitive information from being displayed in
        locations used by administrators for monitoring and troubleshooting, such as log files, the Cloudera Manager
        user interface, and the Impala debug web user interface. You configure regular expressions that match
        sensitive types of information processed by your system, such as credit card numbers or tax IDs, and literals
        matching these patterns are obfuscated wherever they would normally be recorded in log files or displayed in
        administration or debugging user interfaces.
      </p>

      <p>
        In a security context, the log redaction feature is complementary to the Sentry authorization framework.
        Sentry prevents unauthorized users from being able to directly access table data. Redaction prevents
        administrators or support personnel from seeing the smaller amounts of sensitive or personally identifying
        information (PII) that might appear in queries issued by those authorized users.
      </p>

      <p>
        See
        <xref audience="integrated" href="sg_redaction.xml#log_redact"/><xref audience="standalone" href="http://www.cloudera.com/documentation/enterprise/latest/topics/sg_redaction.html" scope="external" format="html"/>
        for details about how to enable this feature and set
        up the regular expressions to detect and redact sensitive information within SQL statement text.
      </p>

    </conbody>

  </concept>

</concept>