Explore how to keep local cache for beamline alignment

[stan-dot]

We need to keep some cache lookup tables for the purposes of beamline alignment. That could be as a local pod-specific *.npy file, or REDIS in a different pod on a cluster. We certainly need some solution for this.

Potential options include:

• https://github.com/bryceadams3/numpy-redis
• write into a file in tmp
• ....?

[callumforrester]

I would recommend that this not become a feature of blueapi, for the sake of keeping it simple and small-scoped. Previously there has been discussion of using databases for lookup tables, I believe MX have had some success with redis. They have also used shared files as a temporary solution until the database was ready.

[DiamondJoseph]

This equates to Redis in a different pod in the namespace, and the plan calls out to it as part of execution, without it being a part of blueapi. Just a pattern for an adaptive scan

plan_start -> fetch values from external -> plan_body -> store values in external -> plan_finish

[DiamondJoseph]

There's also a non-numpy redis python client https://redis.io/docs/latest/develop/connect/clients/python/ for when using it as just key-value storage and don't need the array support

[stan-dot]

@callumforrester this is a necessary feature and the data captured would be cached directly after running the plan.

And we know it's not beamline specific.

Therefore this will be a centrally developed and maintained feature, whether it's a part of blueapi OR a microservice that wraps reddits that blueapi talks to directly is an architectural decision.

and the 'worse is better' style would be to nicely add this into blueapi runner, whether here or in the #504 engine service.

[callumforrester]

@stan-dot Yes, could have a microservice wrapping redis and then interact with it from you own plans, what functionality is needed in the core of blueapi?

[stan-dot]

possible routes with postgres, differing by protocl

REST

• https://github.com/bitnami/charts/tree/main/bitnami/postgresql
• https://github.com/PostgREST/postgrest

gRPC

• https://docs.rs/postgrpc/latest/postgrpc/

graphQL

• https://www.graphile.org/postgraphile/
• https://hasura.io/pricing (self hosted)

[callumforrester]

Of those, I'd be most interested in where you get with graphile

[keeble]

Without trying to be that guy, is it worth stating the specific use(s) for this?

Are we talking things like "we want to change the focal length of the mirror to the sample position, what are the 16 voltages we need for the bimorphs"? (i.e. things which rarely change) or more like "make a note of this motor position, we'll probably want to come back to this position later"? (i.e. a short-term storage)?

[stan-dot]

what I got from the beamline interview is to replace this

dls_sw/i18/scripts/beamlinestuff/i18scans/Lookuptabledcm_i0.py
and the file
"/dls_sw/i18/software/gda/config/lookupTables/Si111/lookuptable_harmonic7.txt"

[stan-dot]

https://github.com/etcd-io/etcd

and

https://github.com/apache/ignite

look the most promising. the former for 46k stars the latter for being in the Apache ecosystem (but less stars)

[DiamondJoseph]

RE: chatting with Stan

We probably want some simple way of tying into a key-value store instance that can be configured per beamline and interacted with as though it was just a dict. This probably lives in dodal as it is generic enough to be useful across beamlines.

e.g.

lookuptables = PersistedStore()
harmonic_7 = lookuptables["harmonic_7"]

def beamline_stub():
    harmonic_7 = do_alignment()
    lookuptables["harmonic_7"] = harmonic_7