Add index to improve performance of fact deletion

[mbruhin]

Hey, I just made a Pull Request!

I saw that the highest load on my backstage DB by far was from the following query:

delete from "facts" where "id" = $1 and "timestamp" < $2

Which is run as part of the fact generation here.

The performance of this query is very slow for a database with a large number of entities or a large history of facts. We could see somewhat better performance by reducing the number of entities or facts per entity, but adding an index would really help.

There is currently an index on ['id', 'entity', 'timestamp'] but not on ['id', 'timestamp']. Adding this index significantly reduces the load on the DB and the overall performance of the tech insights plugin. Here are my DB metrics from when the index was added:

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
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[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage-community/plugin-tech-insights-backend	workspaces/tech-insights/plugins/tech-insights-backend	patch	v2.4.1

[cal5barton]

@Xantier when will this be released? npm is showing that 2.4.1 was released 2 months ago and not yesterday.

[mbruhin]

@cal5barton It will be released when #5303 is merged as part of version 2.4.2.