Checking Slow SQL Statements in ClickHouse

Scenario

The SQL statement query in ClickHouse is slow because the conditions such as partitions, where conditions, and indexes of SQL statements are set improperly. As a result, the overall performance of the database is affected. To solve this problem, MRS provides the function of monitoring slow ClickHouse query statements.

Ongoing Slow Queries

You can query information about slow SQL statements that are being executed but do not return any result.

• Procedure

  For versions earlier than MRS 3.2.0, log in to FusionInsight Manager and choose Cluster > Services > ClickHouse. On the displayed page, click the Query Management tab and then the Ongoing Slow Queries tab.

  Log in to FusionInsight Manager of an MRS 3.2.0 cluster or later, click Cluster, choose Services > ClickHouse, click Logic Cluster, and click the name of the target logical cluster. On the displayed page, choose Query Management > Ongoing Slow Queries.

• Parameters

  Table 1 Slow query parameters

  Parameter	Description
  Server Node IP Address	IP address of the ClickHouseServer instance. To view the IP address, log in to FusionInsight Manager and choose Cluster > Services > ClickHouse. On the displayed page, click the Instance tab.
  Query ID	Unique ID generated internally.
  Query	Slow query SQL statement.
  Start Time	Time when the execution of a slow query SQL statement starts.
  End Time	Time when the execution of a slow query SQL statement ends.
  Duration (s)	Total execution time of a slow query SQL statement, in seconds.
  User	ClickHouse user who executes a slow query SQL statement.
  Client IP Address	IP address of the client that submits a slow query SQL statement.
  Memory Used (MB)	Memory used by a slow query SQL statement, in MB.
  Operation	You can click Terminate to terminate the slow query using a slow query SQL statement.

• Filter conditions

  Select the query condition as required and filter the query results.

  Table 2 Filter conditions

  Condition	Description
  Slow query duration exceeding	Filters the slow queries based on the duration. The value can be 3 (s), 9 (s), 15 (s), or 25 (s).
  By Query ID	Filters the slow queries based on the query ID. Fuzzy search based on the query ID is supported. For example, if the query ID is 111-222-333-444-555, you can enter part of it such as 111-222 or -222-333 to query the needed information.
  By User	Filters the slow queries based on the ClickHouse user. Fuzzy search based on part of a username is supported.
  By Client IP Address	Filters the slow queries based on the IP address of the client that submits slow query SQL statements. Fuzzy search based on part of the client IP address is supported. For example, if the client IP address is 192.168.0.1, you can enter part of it such as 192.168 or 192.168.0 to query the information you need.

Completed Queries

You can query information about slow SQL statements that have been executed and returned results.

UI path:

Log in to FusionInsight Manager of a cluster earlier than MRS 3.2.0 and choose Cluster > Services > ClickHouse. On the displayed page, click the Query Management tab and then the Completed Queries tab.

Log in to FusionInsight Manager of an MRS 3.2.0 cluster or later, click Cluster, choose Services > ClickHouse, click Logic Cluster, and click the name of the target logical cluster. On the displayed page, choose Query Management > Completed Queries.

For details about slow query parameters and filter conditions, see Table 1 and Table 2, respectively.