ClickHouse V UDF

This basic example illustrates a simple sum V powered Clickhouse UDF function

⏱️ Why

Clickhouse is super fast and already has all the functions one could dream. What is this for?

This example is designed to understand the underlying formats and unleash imagination for integrators.

V Function

Create an simple vlang application:

• read input from stdin
• split row values by tabs
• return some output

Example sum function:

import os

fn main() {
        // Parse stdin to array
        data := os.get_lines()
        for line in data {
           // tabSeparated
           tags := line.split('\t')
           // sum integers & return
           sum := tags[0].int() + tags[1].int()
           println(sum)
        }
}

Compile and store into the UDF script directory:

v -o /var/lib/clickhouse/user-scripts/vlang-udf -prod .

The final executable size is < ~92KB all inclusive!

-rwxr-xr-x   1 root root  92K Mar 13 12:49 vlang-udf*

ClickHouse UDF

Create a UDF Function to invoke your vlang application

• use directory /var/lib/clickhouse/user-scripts to store user-scripts

<functions>
    <function>
        <type>executable</type>
        <name>v_sum</name>
        <return_type>UInt64</return_type>
        <argument>
            <type>UInt64</type>
        </argument>
        <argument>
            <type>UInt64</type>
        </argument>
        <format>TabSeparated</format>
        <command>vlang-udf</command>
        <lifetime>0</lifetime>
    </function>
</functions>

Use UDF

SELECT v_sum(10, 20)

Query id: f98a5f83-4e94-41d0-9d9f-78b37d3af152

┌─v_sum(10, 20)─────┐
│                30 │
└───────────────────┘

1 rows in set. Elapsed: 0.006 sec.