Managing queries

Understand to manage queries for Lenses SQL Snapshot concepts engine for Apache Kafka

Termination Control

SELECT * FROM topicA WHERE _key.deviceId=123 LIMIT 10

Adding a LIMIT 10 in the SQL query will result in the SQL terminating early, as soon as 10 x messages have been discovered. It’s not a perfect solution as we might never find 10 x messages, and thus perform a full scan.

You can also set a maximum query or idle time:

SET max.query.time = 30s;

or max idle time, the idea is that there is no reason to keep polling if we have exhausted the entire topic:

SET max.idle.time = 5s;

or a maximum amount of data to read from Kafka. This controls how much data to read from Kafka NOT the required memory.

SET max.size = 1M;

Recent queries

Recent queries are displayed, but only for the current session, they are not currently retained.

Click on the play button to run a previous query. If a query is already running, you will be asked if you want to stop it first.

View All queries

SHOW ALL QUERIES

View Running queries

You can see all running queries by Lenses users using SQL:

SHOW QUERIES

Kill Running queries

You can force stop a query by another user using SQL:

KILL QUERY <id>

Concurrent queries limit

Starting with 6.1.3 version, there's a global limit on concurrent queries, as well as a limit per user. They can be set via the agent configuration:

lenses.sql.settings.max.concurrent.queries=200
lenses.sql.settings.max.concurrent.queries.per.user=2