ClickHouse KILL Statement
There are two kinds of kill statements: to kill a query and to kill a mutation. KILL QUERY Attempts to forcibly terminate the currently running queries. The queries to terminate are selected from the system.processes […]
Articles by Can Sayn
ClickHouse Recommended Troubleshooting Metrics
Alert Name Shell or SQL command Severity ClickHouse status $ curl ‘http://localhost:8123/’ Ok. Critical Too many simultaneous queries. Maximum: 100 (by default) select value from system.metrics where metric=’Query’ Critical Replication status $ curl ‘http://localhost:8123/replicas_status’ Ok. […]
How To Check Table and Column Sizes In ClickHouse
With system tables, you can learn the details of the tables and columns on ClickHouse with the following queries. In this article, we will explain two system tables and give examples. First, system.parts table. […]
How to Configure Data Skipping Indexes in ClickHouse for Query Performance
Introduction to Data Skipping Indexes When working on ClickHouse, many different factors can affect its performance of Clickhouse. One of the most critical elements is that ClickHouse determines whether it will use a primary key […]
ClickHouse Upgrade Simplified
Upgrading and downgrading on ClickHouse is a quite simple operation. In this article, we will explain how to do these operations with examples. For the upgrade process, you can start the upgrade process by typing […]
ClickHouse Query Troubleshooting
ClickHouse has tables called ‘system.query_log’ and ‘system_query_thread_log’ that are used for storing statistics of each executed query like duration, memory usage, peak memory usage, etc. There is also a table called ‘system.processes’ that has information about […]
Aggregate Functions via ClickHouse
Introduction Functions that arrive at the resultant value by calculating on a set of values are called aggregation functions. In ClickHouse, aggregate functions work in the normal way as expected by database expert. In this […]
ClickHouse June 2022 Release – v22.6
Introduction This article will introduce the new features defined in the new version of ClickHouse, version 22.6. For more information please visit official ClickHouse docs here. Download the ClickHouse 22.6 release here. ClickHouse Release 22.6 […]
Demystifying JSON Data With ClickHouse
Introduction JSON refers to Javascript Object Notation. It is a popular text data format used to exchange data on modern web and mobile applications. It is based on a subset of the Javascript programming language. […]
How to implement Bloom Filters in ClickHouse for Query Performance
Introduction A Bloom filter is a data structure that tells the user whether a particular item is part of a set. Although it cannot definitively tell if an item is in the set, it can […]