Document MV GRACE PERIOD clause

[findepi]

Doc changes for changes added in #15104
Per #15326 issue.

[mosabua]

Re "defaults to infinity". We should clarify what that means in practice. Something like that:

As a result a materialized by default therefore without the specified grace period always uses the materialized data from the last refresh and never falls back to act like a view and retrieve the current data from the source tables.

[findepi]

Thanks for pointing this out.
You worded it very precisely. I am afraid some users may not understand. The sentence feels pretty long. Would it be possible to reword it or split?

Ideally, can you please make it a suggestion, or somehow else indicate which piece of text you would want to have replaced with the new sentence(s)?

[mosabua]

Yeah .. I was struggling putting something together.

How about this? After "inifinity." insert this:

The default behavior therefore is that the queries accessing the materialized view always access the data from the most recent refresh and the materialized view storage tables. The query processing never falls back to process the materialized view access like a view and retrieve the current data from the source tables. This only occurs if a grace period is specified.

I know this is long but I feel like this is the only way to truly explain what is and is not happening. Maybe @colebow can chime in and refine my wording some more.

[mosabua]

@findepi did you forget to pull the above suggestion in?

[mosabua]

Also .. related question .. I am not 100% sure so could you clarify / confirm .. is this a breaking change for MVs that are already defined?

[findepi]

@mosabua see #15326 and #15326 (comment) in particular.

[mosabua]

So at this stage the code change is a breaking change. I am not sure if and how we want to communicate this in the release notes @martint @colebow but it also looks like it is a bit late for that since this was merged on the 16th of December so it shipped already with 405.

[findepi]

but it also looks like it is a bit late for that since this was merged on the 16th of December so it shipped already with 405.

Only the syntax, so the breakage didn't happen yet.

However, I am not prepared to discuss breaking changes mitigations on a docs PR.
I am not breaking docs here, or anything else.

[mosabua]

but it also looks like it is a bit late for that since this was merged on the 16th of December so it shipped already with 405.

Only the syntax, so the breakage didn't happen yet.

However, I am not prepared to discuss breaking changes mitigations on a docs PR. I am not breaking docs here, or anything else.

Sounds good.

[colebow]

LGTM.

[findepi]

Thanks you @mosabua @colebow @ebyhr for your review!

I've took the what we ended up with and put it together with code changes here: #15842