Error Policy

An error policy defines how a metric collector handles specific MySQL errors. Error policies are optional, and most metric collectors do not define any. To see which collectors have error policies, check the domain reference or use --print-domains:

$ blip --print-domains

repl
	Replication status

	(No options)

	Errors:
		access-denied: MySQL error 1227: access denied on 'SHOW REPLICA STATUS' (need REPLICATION CLIENT priv)

	Metrics:
		running (gauge): 1=running (no error), 0=not running, -1=not a replica

The output above is truncated to highlight the error policy that the repl collector handles: access-denied. If MySQL returns error 1227 to the collector, it handles the error according to the error policy if defined. The default error policy is report,drop,retry: report the error, drop the metric, and retry.

Default error policy: report,drop,retry: report the error, drop the metric, and retry.

A different error policy can be specified for the collector in the plan:

collect:
  repl:
    metrics:
      - running
    errors:
      access-denied: "ignore,drop,stop"  # New error policy; override default

In the example above, instead of the default (report,drop,retry), the collector will ignore the error, drop the metric, and stop trying to collect it. The format of the error policy value is defined in the next section.

Since error policies handle specific MySQL errors, they are not intended for general error handling. Instead, error policies make it possible to write plans that are “best effort” depending on the MySQL instance: if a collector works, then great; but if not, an error policy prevents Blip from spewing errors.

An error policy value is a string and comma-separated value with three parts: <report>,<metric>,<retry>

Report:

• ignore: Silently ignore the error; report nothing (not even an event)
• report: Report the metric (default)
• report-once: Report the metric only the first time it occurs, then ignore further errors

Metric:

• drop: Drop the metric (default)
• zero: Report zero value

Retry:

• retry: Keep trying to collect metric (default)
• stop: Stop collecting metric