Update architecture docs based on "Life of a Query" tech note

[rmloveland]

Richard Loveland (rmloveland) commented:

We have recently (June 2021) seen some very nice updates to the "life of a query" tech note in the CRDB repo.

We should review the content of "life of a query" and port those parts of it that are appropriate for end users to the relevant sections of the CockroachDB architecture docs.

See also:

• Update 'Life of a Distributed Transaction' with Parallel Commits info, as needed #5467
• Review / update architecture docs based on CRDB SIGMOD paper #10794

Jira Issue: DOC-1541

[ianjevans]

As part of these updates, it'd be great to have a more focused discussion of our requirements and recommendations for the number of replicas, the number of availability zones, and the number of nodes within a cluster.

From Slack:

A customer asked me today if we have any docs that point out that it's a best practice to use an odd number of replicas (3, 5, 7, etc.) -- and I can't find one
I think there should be one.

This has also come up as a hole in our architecture in CockroachCloud, when creating a multi-region cluster. We have a couple places where we assert the minimum or recommended values within regions and zones but don't really have a higher-level doc that explains why those minimums/recommendations are present.

[rmloveland]

Makes sense, thanks for capturing this Ian! Also relates to #9239

[mwang1026]

Related:
#5467
#4279

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