Use k6 to load test log queries

When designing a test scenario for load testing the read path of a Loki installation, it is important to know what types of queries you expect.

Supported query types

Loki has 5 types of queries:

instant query
range query
labels query
label values query
series query

In a real-world use-case, such as querying Loki using it as a Grafana data source, all of these queries are used. Each of them has a different API endpoint. The xk6-loki extension provides a Javascript API for all these query types.

Instant query

Instant queries can be executed using the function instantQuery(query, limit) on the loki.Client instance:

Javascript example code fragment:

export default () => {
  client.instantQuery(`rate({app="my-app-name"} | logfmt | level="error" [5m])`);
}

Range query

Range queries can be executed using the function rangeQuery(query, duration, limit) on the loki.Client instance:

Javascript example code fragment:

export default () => {
  client.rangeQuery(`{app="my-app-name"} | logfmt | level="error"`, "15m");
}

Labels query

Labels queries can be executed using the function labelsQuery(duration) on the loki.Client instance:

Javascript example code fragment:

export default () => {
  client.labelsQuery("10m");
}

Label values query

Label values queries can be executed using the function labelValuesQuery(label, duration) on the loki.Client instance:

Javascript example code fragment:

export default () => {
  client.labelValuesQuery("app", "10m");
}

Series query

Series queries can be executed using the function seriesQuery(matcher, range) on the loki.Client instance:

Javascript example code fragment:

export default () => {
  client.seriesQuery(`match[]={app=~"loki-.*"}`, "10m");
}

Metrics

The extension collects metrics that are printed in the end-of-test summary in addition to the built-in metrics. These metrics are collected only for instant and range queries.

name	description
`loki_bytes_processed_per_second`	amount of bytes processed by Loki per second
`loki_bytes_processed_total`	total amount of bytes processed by Loki
`loki_lines_processed_per_second`	amount of lines processed by Loki per second
`loki_lines_processed_total`	total amount of lines processed by Loki

Labels pool

With the xk6-loki extension, you can use the field labels on the Config object. It contains label names and values that are generated in a reproducible manner. Use the same labels cardinality configuration for both write and read testing.

Javascript example code fragment:

const labelCardinality = {
  "app": 5,
  "namespace": 2,
};
const conf = new loki.Config(BASE_URL, 10000, 1.0, labelCardinality);
const client = new loki.Client(conf);

function randomChoice(items) {
  return items[Math.floor(Math.random() * items.length)];
}

export default() {
  let app = randomChoice(conf.labels.app);
  let namespace = randomChoice(conf.labels.namespace);
  client.rangeQuery(`{app="${app}", namespace="${namespace}"} | logfmt | level="error"`, "15m");
}

Alternatively, you can define your own pool of label names and values, and then randomly select labels from your pool instead of a generated pool.

Javascript example

A more complex example of a read scenario can be found in xk6-loki repository. The test file read-scenario.js can be resused and extended for your needs.

It allows you to configure ratios for each type of query and the ratios of time ranges.

Javascript example:

const queryTypeRatioConfig = [
  {
    ratio: 0.1,
    item: readLabels
  },
  {
    ratio: 0.15,
    item: readLabelValues
  },
  {
    ratio: 0.05,
    item: readSeries
  },
  {
    ratio: 0.5,
    item: readRange
  },
  {
    ratio: 0.2,
    item: readInstant
  },
];

This configuration would execute approximately