Impala Web User Interface for Debugging
The impalad web UI (default port: 25000) includes information about configuration settings, running and completed queries, and associated performance and resource usage for queries. In particular, the Details link for each query displays alternative views of the query including a graphical representation of the plan, and the output of the EXPLAIN, SUMMARY, and PROFILE statements from impala-shell. Each host that runs the impalad daemon has its own instance of the web UI, with details about those queries for which that host served as the coordinator. To get a consolidated view for all queries, it is usually more convenient to use the charts, graphs, and other monitoring features in Cloudera Manager. The impalad web UI is mainly for diagnosing query problems that can be traced to a particular node.
The statestored web UI (default port: 25010) includes information about memory usage, configuration settings, and ongoing health checks performed by this daemon. Because there is only a single instance of this daemon within any cluster, you view the web UI only on the particular host that serves as the Impala Statestore.
The catalogd web UI (default port: 25020) includes information about the databases, tables, and other objects managed by Impala, in addition to the resource usage and configuration settings of the daemon itself. The catalog information is represented as the underlying Thrift data structures. Because there is only a single instance of this daemon within any cluster, you view the web UI only on the particular host that serves as the Impala Catalog Server.
Debug Web UI for impalad
To debug and troubleshoot the impalad daemon using a web-based interface, open the URL http://impala-server-hostname:25000/ in a browser. (For secure clusters, use the prefix https:// instead of http://.) Because each Impala node produces its own set of debug information, choose a specific node that you are curious about or suspect is having problems.
By default, the main page of the debug web UI is at http://impala-server-hostname:25000/ (non-secure cluster) or https://impala-server-hostname:25000/ (secure cluster).
This page lists the version of the impalad daemon, plus basic hardware and software information about the corresponding host, such as information about the CPU, memory, disks, and operating system version.
By default, the backends page of the debug web UI is at http://impala-server-hostname:25000/backends (non-secure cluster) or https://impala-server-hostname:25000/backends (secure cluster).
This page lists the host and port info for each of the impalad nodes in the cluster. Because each impalad daemon knows about every other impalad daemon through the statestore, this information should be the same regardless of which node you select. Links take you to the corresponding debug web pages for any of the other nodes in the cluster.
By default, the catalog page of the debug web UI is at http://impala-server-hostname:25000/catalog (non-secure cluster) or https://impala-server-hostname:25000/catalog (secure cluster).
This page displays a list of databases and associated tables recognized by this instance of impalad. You can use this page to locate which database a table is in, check the exact spelling of a database or table name, look for identical table names in multiple databases, and so on.
By default, the logs page of the debug web UI is at http://impala-server-hostname:25000/logs (non-secure cluster) or https://impala-server-hostname:25000/logs (secure cluster).
This page shows the last portion of the impalad.INFO log file, the most detailed of the info, warning, and error logs for the impalad daemon. You can refer here to see the details of the most recent operations, whether the operations succeeded or encountered errors. This central page can be more convenient than looking around the filesystem for the log files, which could be in different locations on clusters that use Cloudera Manager or not.
By default, the memz page of the debug web UI is at http://impala-server-hostname:25000/memz (non-secure cluster) or https://impala-server-hostname:25000/memz (secure cluster).
This page displays summary and detailed information about memory usage by the impalad daemon. You can see the memory limit in effect for the node, and how much of that memory Impala is currently using.
By default, the metrics page of the debug web UI is at http://impala-server-hostname:25000/metrics (non-secure cluster) or https://impala-server-hostname:25000/metrics (secure cluster).
This page displays the current set of metrics: counters and flags representing various aspects of impalad internal operation. For the meanings of these metrics, see Impala Metrics in the Cloudera Manager documentation.
By default, the queries page of the debug web UI is at http://impala-server-hostname:25000/queries (non-secure cluster) or https://impala-server-hostname:25000/queries (secure cluster).
This page lists all currently running queries, plus any completed queries whose details still reside in memory. The queries are listed in reverse chronological order, with the most recent at the top. (You can control the amount of memory devoted to completed queries by specifying the --query_log_size startup option for impalad.)
On this page, you can see at a glance how many SQL statements are failing (State value of EXCEPTION), how large the result sets are (# rows fetched), and how long each statement took (Start Time and End Time).
Each query has an associated link that displays the detailed query profile, which you can examine to understand the performance characteristics of that query. See Using the Query Profile for Performance Tuning for details.
By default, the sessions page of the debug web UI is at http://impala-server-hostname:25000/sessions (non-secure cluster) or https://impala-server-hostname:25000/sessions (secure cluster).
This page displays information about the sessions currently connected to this impalad instance. For example, sessions could include connections from the impala-shell command, JDBC or ODBC applications, or the Impala Query UI in the Hue web interface.
By default, the threadz page of the debug web UI is at http://impala-server-hostname:25000/threadz (non-secure cluster) or https://impala-server-hostname:25000/threadz (secure cluster).
This page displays information about the threads used by this instance of impalad, and shows which categories they are grouped into. Making use of this information requires substantial knowledge about Impala internals.
By default, the varz page of the debug web UI is at http://impala-server-hostname:25000/varz (non-secure cluster) or https://impala-server-hostname:25000/varz (secure cluster).
This page shows the configuration settings in effect when this instance of impalad communicates with other Hadoop components such as HDFS and YARN. These settings are collected from a set of configuration files; Impala might not actually make use of all settings.
The bottom of this page also lists all the command-line settings in effect for this instance of impalad. See Modifying Impala Startup Options for information about modifying these values.