Clarify use of read replicas

[grubbins]

The docs suggest that reads are evenly distributed between the master DB and the read replica DBs. Based on both the server code and the observed behaviour, I do not believe that is the case - I believe that (if any read replicas are available) read queries are distributed among the read replicas only. This is a useful distinction to keep in mind for site admins.

[mattermost-build]

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[agnivade]

The original text is technically correct. While it's true that 99% of times, read requests are sent to the read replicas, there are cases where they aren't. If you want to change the text to reflect this, we can do it. Otherwise we can leave it as is.

[grubbins]

Yes - I think there's a big difference between "Mattermost distributes read requests across all databases", and "Mattermost distributes almost all read requests across the read replicas only". Would indeed like to see an update...

Are you asking me to propose different wording?

[cwarnermm]

@grubbins - We'd welcome your docs contribution with updated, clarified wording if you're open to it.

[grubbins]

OK - please see what you think of my latest wording.

[cwarnermm]

Thank you so much, @grubbins!

[grubbins]

Oops - I think the markdown requires a linebreak before the bullet points. The html currently up on the docs page has them as inline asterisks.

Could you insert the linebreak @cwarnermm ? Or do you need me to open a new PR with it?

[cwarnermm]

I'm happy to update the formatting, @grubbins!

[cwarnermm]

Fixed via #6627