ClickHouse/docs/en/operations/troubleshooting.md

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46	Troubleshooting

Troubleshooting

• Installation
• Connecting to the server
• Query processing
• Efficiency of query processing

Installation

You Cannot Get Deb Packages from ClickHouse Repository with Apt-get

• Check firewall settings.
• If you cannot access the repository for any reason, download packages as described in the Getting started article and install them manually using the sudo dpkg -i <packages> command. You will also need the tzdata package.

Connecting to the Server

Possible issues:

• The server is not running.
• Unexpected or wrong configuration parameters.

Server Is Not Running

Check if server is runnnig

Command:

$ sudo service clickhouse-server status

If the server is not running, start it with the command:

$ sudo service clickhouse-server start

Check logs

The main log of clickhouse-server is in /var/log/clickhouse-server/clickhouse-server.log by default.

If the server started successfully, you should see the strings:

• <Information> Application: starting up. — Server started.
• <Information> Application: Ready for connections. — Server is running and ready for connections.

If clickhouse-server start failed with a configuration error, you should see the <Error> string with an error description. For example:

2019.01.11 15:23:25.549505 [ 45 ] {} <Error> ExternalDictionaries: Failed reloading 'event2id' external dictionary: Poco::Exception. Code: 1000, e.code() = 111, e.displayText() = Connection refused, e.what() = Connection refused

If you don’t see an error at the end of the file, look through the entire file starting from the string:

<Information> Application: starting up.

If you try to start a second instance of clickhouse-server on the server, you see the following log:

2019.01.11 15:25:11.151730 [ 1 ] {} <Information> : Starting ClickHouse 19.1.0 with revision 54413
2019.01.11 15:25:11.154578 [ 1 ] {} <Information> Application: starting up
2019.01.11 15:25:11.156361 [ 1 ] {} <Information> StatusFile: Status file ./status already exists - unclean restart. Contents:
PID: 8510
Started at: 2019-01-11 15:24:23
Revision: 54413

2019.01.11 15:25:11.156673 [ 1 ] {} <Error> Application: DB::Exception: Cannot lock file ./status. Another server instance in same directory is already running.
2019.01.11 15:25:11.156682 [ 1 ] {} <Information> Application: shutting down
2019.01.11 15:25:11.156686 [ 1 ] {} <Debug> Application: Uninitializing subsystem: Logging Subsystem
2019.01.11 15:25:11.156716 [ 2 ] {} <Information> BaseDaemon: Stop SignalListener thread

See system.d logs

If you don’t find any useful information in clickhouse-server logs or there aren’t any logs, you can view system.d logs using the command:

$ sudo journalctl -u clickhouse-server

Start clickhouse-server in interactive mode

$ sudo -u clickhouse /usr/bin/clickhouse-server --config-file /etc/clickhouse-server/config.xml

This command starts the server as an interactive app with standard parameters of the autostart script. In this mode clickhouse-server prints all the event messages in the console.

Configuration Parameters

Check:

• Docker settings.

  If you run ClickHouse in Docker in an IPv6 network, make sure that network=host is set.

• Endpoint settings.

  Check listen_host and tcp_port settings.

  ClickHouse server accepts localhost connections only by default.

• HTTP protocol settings.

  Check protocol settings for the HTTP API.

• Secure connection settings.

  Check:

  • The tcp_port_secure setting.
  • Settings for SSL sertificates.

  Use proper parameters while connecting. For example, use the port_secure parameter with clickhouse_client.

• User settings.

  You might be using the wrong user name or password.

Query Processing

If ClickHouse is not able to process the query, it sends an error description to the client. In the clickhouse-client you get a description of the error in the console. If you are using the HTTP interface, ClickHouse sends the error description in the response body. For example:

$ curl 'http://localhost:8123/' --data-binary "SELECT a"
Code: 47, e.displayText() = DB::Exception: Unknown identifier: a. Note that there are no tables (FROM clause) in your query, context: required_names: 'a' source_tables: table_aliases: private_aliases: column_aliases: public_columns: 'a' masked_columns: array_join_columns: source_columns: , e.what() = DB::Exception

If you start clickhouse-client with the stack-trace parameter, ClickHouse returns the server stack trace with the description of an error.

You might see a message about a broken connection. In this case, you can repeat the query. If the connection breaks every time you perform the query, check the server logs for errors.

Efficiency of Query Processing

If you see that ClickHouse is working too slowly, you need to profile the load on the server resources and network for your queries.

You can use the clickhouse-benchmark utility to profile queries. It shows the number of queries processed per second, the number of rows processed per second, and percentiles of query processing times.