Prometheus connector

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

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 Trino query table name, 21d is the duration of the query. The Prometheus time value corresponds to the TIMESTAMP field. Trino queries are translated from their use of the TIMESTAMP field to a duration and time value as needed. Trino splits are generated by dividing the query range into attempted equal chunks.

Requirements

To query Prometheus, you need:

• Network access from the Trino coordinator and workers to the Prometheus server. The default port is 9090.
• Prometheus version 2.15.1 or later.

Configuration

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

connector.name=prometheus
prometheus.uri=http://localhost:9090
prometheus.query.chunk.size.duration=1d
prometheus.max.query.range.duration=21d
prometheus.cache.ttl=30s
prometheus.bearer.token.file=/path/to/bearer/token/file
prometheus.read-timeout=10s

Configuration properties

The following configuration properties are available:

Prometheus configuration properties

Property name	Description	Default
prometheus.uri	Where to find Prometheus coordinator host.	http://localhost:9090
prometheus.query.chunk.size.duration	The duration of each query to Prometheus. The equivalent catalog session property is query_chunk_size_duration.	1d
prometheus.max.query.range.duration	Width of overall query to Prometheus, will be divided into prometheus.query.chunk.size.duration queries. The equivalent catalog session property is max_query_range_duration.	21d
prometheus.cache.ttl	How long values from this config file are cached.	30s
prometheus.read-timeout	How much time a query to Prometheus has before timing out.	10s
prometheus.auth.user	Username for basic authentication.
prometheus.auth.password	Password for basic authentication.
prometheus.auth.http.header.name	Name of the header to use for authorization.	Authorization
prometheus.bearer.token.file	File holding bearer token if needed for access to Prometheus.
prometheus.read-timeout	How much time a query to Prometheus has before timing out.	10s
prometheus.case-insensitive-name-matching	Match Prometheus metric names case insensitively.	false
prometheus.http.additional-headers	Additional headers to send to Prometheus endpoint. These headers must be comma-separated and delimited using :. For example, header1:value1,header2:value2 sends two headers header1 and header2 with the values as value1 and value2. Escape comma (,) or colon(:) characters in a header name or value with a backslash (\).

Not exhausting your Trino available heap

The prometheus.query.chunk.size.duration and prometheus.max.query.range.duration are values to protect Trino from too much data coming back from Prometheus. The prometheus.max.query.range.duration is the item of particular interest.

On a Prometheus instance that has been running for a while 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.size.duration to 10m, dividing the query window into 6 queries each of which can be handled in a Trino 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 example:

SELECT * FROM example.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.
prometheus.auth.http.header.name allows you to use a custom header name for bearer token. Default value is Authorization.

Type mapping

Because Trino and Prometheus each support types that the other does not, this connector modifies some types when reading data.

The connector returns fixed columns that have a defined mapping to Trino types according to the following table:

Prometheus column to Trino type mapping

Prometheus column	Trino type
labels	MAP(VARCHAR,VARCHAR)
TIMESTAMP	TIMESTAMP(3) WITH TIMEZONE
value	DOUBLE

No other types are supported.

The following example query result shows how the Prometheus up metric is represented in Trino:

SELECT * FROM example.default.up;

                        labels                         |           timestamp            | value
--------------------------------------------------------+--------------------------------+-------
{instance=localhost:9090, job=prometheus, __name__=up} | 2022-09-01 06:18:54.481 +09:00 |   1.0
{instance=localhost:9090, job=prometheus, __name__=up} | 2022-09-01 06:19:09.446 +09:00 |   1.0
(2 rows)

SQL support

The connector provides globally available and read operation statements to access data and metadata in Prometheus.