Using Impala Logging

The Impala logs record information about:


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 /var/log/impala/profiles. You can access them through the Impala web user interface. For example, at http://impalad-node-hostname:25000/queries, each query is followed by a Profile link leading to a page showing extensive analytical data for the query execution.

The auditing feature introduced in Impala 1.1.1 produces a separate set of audit log files when enabled. See Auditing Impala Operations for details.

In Impala 2.9 and higher, you can control how many audit event log files are kept on each host through the ‑‑max_audit_event_log_files startup option for the impalad daemon, similar to the ‑‑max_log_files option for regular log files.

The lineage feature introduced in Impala 2.2.0 produces a separate lineage log file when enabled. See Viewing Lineage Information for Impala Data for details.

Locations and Names of Impala Log Files

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

Rotating Impala Logs

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.

Impala can automatically remove older unneeded log files, a feature known as log rotation.

In Impala 2.2 and higher, the ‑‑max_log_files configuration option specifies how many log files to keep at each severity level (INFO, WARNING, ERROR, and FATAL). You can specify an appropriate setting for each Impala-related daemon (impalad, statestored, and catalogd).
  • 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.
  • The default value is 10.

Impala checks to see if any old logs need to be removed based on the interval specified in the ‑‑logbufsecs setting, every 5 seconds by default.

For some log levels, Impala logs are first temporarily buffered in memory and only written to disk periodically. The ‑‑logbufsecs setting controls the maximum time that log messages are buffered for. For example, with the default value of 5 seconds, there may be up to a 5 second delay before a logged message shows up in the log file.

It is not recommended that you set ‑‑logbufsecs to 0 as the setting makes the Impala daemon to spin in the thread that tries to delete old log files.

Changing Log Levels Dynamically

For debugging purposes you may be adjusting the logging configuration for Catalog and impalad servers. This required restarting the services. Impala supports adjusting the log levels dynamically without the need to restart the server. There is a /log_level tab in the debug page of all Impala servers. You can query the log4j log level of root or org.apache.impala by using the Get Java Log Level button. Also you can change the vlog/log4j levels to any supported levels of logging. You can select the log level using the LOG LEVEL drop down box. You also have an option to restore the log levels to their original configuration by using the RESET button.

Here is the format of a Glog:

${level}${month}${day} HH:MM:SS.${us} ${thread-id} ${source-file}:${line}] ${query-id}] ${message}


Reviewing Impala Logs

By default, the Impala log is stored at /var/log/impalad/. The most comprehensive log, showing informational, warning, and error messages, is in the file name impalad.INFO. 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 impalad.WARNING and/or impalad.ERROR files, which contain the subsets of messages indicating potential problems.)


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

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

[user@example impalad]$ pwd
[user@example impalad]$ more impalad.INFO
Log file created at: 2013/01/07 08:42:12
Running on machine:
Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msg
I0107 08:42:12.292155 14876] impalad version 0.4 RELEASE (build 9d7fadca0461ab40b9e9df8cdb47107ec6b27cff)
Built on Fri, 21 Dec 2012 12:55:19 PST
I0107 08:42:12.292484 14876] Using hostname:
I0107 08:42:12.292706 14876] Flags (see also /varz are on debug webserver):
Note: The preceding example shows only a small part of the log file. Impala log files are often several megabytes in size.

Understanding Impala Log Contents

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

Setting Logging Levels

Impala uses the GLOG system, which supports three logging levels. You can adjust logging levels by exporting variable settings. To change logging settings manually, use a command similar to the following on each node before starting impalad:

export GLOG_v=1
Note: For performance reasons, do not enable the most verbose logging level of 3 unless there is no other alternative for troubleshooting.

For more information on how to configure GLOG, including how to set variable logging levels for different system components, see documentation for the glog project on github.

Understanding What is Logged at Different Logging Levels

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.

Increasing logging levels imposes performance overhead and increases log size. Where practical, use GLOG_v=1 for most cases: this level has minimal performance impact but still captures useful troubleshooting information.

Additional information logged at each level is as follows:

  • GLOG_v=1 - The default level. Logs information about each connection and query that is initiated to an impalad instance, including runtime profiles.
  • 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.
  • 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.

Redacting Sensitive Information from Impala Log Files

Log redaction is a security feature that prevents sensitive information from being displayed in locations used by administrators for monitoring and troubleshooting, such as log files 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.

In a security context, the log redaction feature is complementary to the Ranger authorization framework. Ranger 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.

See the documentation for your Apache Hadoop distribution for details about how to enable this feature and set up the regular expressions to detect and redact sensitive information within SQL statement text.