Looks good to me, but it would really be nice to have a bit more documentation/explanation on how stuff work and are organized in Cassandra, be it in the code itself and as docu material in doc/

typos

In T2003#41459, @vlorentz wrote:

In T2003#41457, @douardda wrote:

One question could be 'what is the definitive source of truth in our stack?'

I assumed we wanted to aim for Kafka to be the source of truth

In T2003#41456, @olasd wrote:

Now that I think of it, we can decompose this in stages in the storage pipeline:

• add an input validating proxy high up the stack
• replace the journal writer calls sprinkled in all methods with a journal writing proxy
• add a "don't insert objects" filter low down the stack

so we'd end up with the following pipeline for workers:

• input validation proxy
• object bundling proxy
• object deduplication against read-only proxy
• journal writer proxy
• addition-blocking filter
• underlying read-only storage

and the following pipeline for the "main storage replayer":

• underlying read-write storage

(it's a very short pipeline... a pipedash?)

In T2003#41443, @vlorentz wrote:

We already discussed this at the time we replaced the journal-publisher with journal-writer. Adding to Kafka after inserting to the DB means that Kafka will be missing some messages, and we would need to run a backfiller on a regular basis to fix it.

In T2003#41428, @olasd wrote:

This component would centralize the "has this object already appeared?" logic, as well as the queueing+retry logic, and would replace the current kafka mirror component.

How does that sound?

In T2003#41429, @olasd wrote:

Key metrics for the filter component:

• kafka consumer offset
• min(latest_attempt) where in_flight = true (time it takes for a message from submission in the buffer to (re-)processing by the filter; should stay close to the current time)
• count(*) where given_up = false group by topic (number of objects pending a retry, should be small)
• count(*) where in_flight = true group by topic (number of objects buffered for reprocessing, should be small)
• max(latest_attempt) (last processing time by the requeuing process)
• count(*) where given_up = true (checks whether the housekeeping process)

Note: haven't read the other comment below, just reacting at this one as I am reading it.

Is this still "a thing"?

Since T1914 is high priority, this one is too.

What is the status of this issue? Do we still face this bug?

Agreed, this no longer need to be a high priority task.

Fix typos and address ardumont's comments

closed by 490c2454749679186ffca9cdd3f480e50d2147c2

In D2552#60770, @vlorentz wrote:

Why does setup_pip call scheduler_host.check_output()?

Not a definitive solution but as discussed IRL, let's quick fix the cran lister then refactor it "the proper way"

I'm fine with the code, but as I already said, I'd really like the commit message to have a paragraph on why this is needed and what problem it solves.