Where to put metadata in Dagster

[sryza]

Dagster has a few different vehicles for attaching metadata - op tags, run tags, job metadata, asset definition metadata, asset materialization metadata, asset observation metadata.

When is it appropriate to use each one of these?

• Asset materialization metadata - metadata about an asset that was just materialized. E.g. "number of rows in the table" or "number of bytes in the file".
• Asset observation metadata - similar to asset materialization metadata, e.g. "number of rows in the table" or "number of bytes in the file", but usually recorded for assets that were not materialized by Dagster.
• Asset definition metadata - metadata that describes how an asset is expected to look and its role within an organization. E.g. "owner", "columns".
• Op tags - describes an op. E.g. "uses Spark", "needs a GPU".
• Run tags - metadata attached to a run. E.g. "triggered by Bob" or "targets partition 2022-02-01".
• Job metadata - metadata about a job. E.g. "owner".