# Prometheus Connector#

The Prometheus connector allows reading Prometheus.metrics as tables in Presto.

The mechanism for querying Prometheus is to use the Prometheus HTTP API. Specifically, all queries are resolved to Prometheus Instant queries with a form like: http://localhost:9090/api/v1/query?query=up[21d]&time=1568229904.000” In this case the up metric is taken from the Presto query table name. 21d is the duration of the query. The Prometheus time value corresponds to the timestamp field. Presto queries are translated from their use of the timestamp field to a duration and time value as needed. Presto splits are generated by dividing the query range into attempted equal chunks.

## Configuration#

Create etc/catalog/prometheus.properties to mount the Prometheus connector as the prometheus catalog, replacing the properties as appropriate:

connector.name=prometheus
prometheus.uri=http://localhost:9090
prometheus.query-chunk-duration=1d
prometheus.max-query-duration=1h
prometheus.cache-ttl=30s
prometheus.bearer-token-file=/path/to/bearer/token/file


## Configuration Properties#

The following configuration properties are available:

Property Name

Description

prometheus.uri

prometheus.query-chunk-duration

The duration of each query to Prometheus

prometheus.max-query-duration

Width of overall query to Prometheus, will be divided into query-chunk-duration queries

prometheus.cache-ttl

How long the config values are cached

prometheus.bearer-token-file

## Not Exhausting Your Presto Available Heap#

The prometheus.query-chunk-duration and prometheus.max-query-duration are values to protect Presto from fetching too much data from Prometheus. The prometheus.max-query-duration is the item of particular interest.

On a Prometheus instance that has been running for awhile and depending on data retention settings, 21d might be far too much. Perhaps 1h might be a more reasonable setting. In the case of 1h it might be then useful to set prometheus.query-chunk-duration to 10m, dividing the query window into 6 queries each of which can be handled in a Presto split.

Primarily query issuers can limit the amount of data returned by Prometheus by taking advantage of WHERE clause limits on timestamp, setting an upper bound and lower bound that define a relatively small window. For instance:

SELECT * FROM prometheus.default.up WHERE timestamp > (NOW() - INTERVAL '10' second);


If the query does not include a WHERE clause limit, these config settings are meant to protect against an unlimited query.

## Bearer Token Authentication#

Prometheus can be setup to require a Authorization header with every query. The value in prometheus.bearer-token-file allows for a bearer token to be read from the configured file. This file is optional and not required unless your Prometheus setup requires it.