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:

Property name	Description
`prometheus.uri`	Where to find Prometheus coordinator host
`prometheus.query.chunk.size.duration`	The duration of each query to Prometheus
`prometheus.max.query.range.duration`	Width of overall query to Prometheus, will be divided into query-chunk-size-duration queries
`prometheus.cache.ttl`	How long values from this config file are cached
`prometheus.auth.user`	Username for basic authentication
`prometheus.auth.password`	Password for basic authentication
`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
`prometheus.case-insensitive-name-matching`	Match Prometheus metric names case insensitively. Defaults to `false`

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 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.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.

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.