sqlliveness: encode region in session id

[jeffswenson]

Encode a region enum in the sqlliveness session id. The region will be used to support converting the sqlliveness and sql_instances table to regional by row tables.

This change creates a custom encoding for the session id. The encoding is convenient, as it allows adding a region to the session id without requiring modifications to the jobs table or the
crdb_internal.sql_liveness_is_alive built in.

The enum.One value is a work around for the fact the system database does not include a region enum by default. In the absence of a region enum, enum.One will be used in the session.

Part of #85736

Release note: None

[cockroach-teamcity]

This change is 

[jeffswenson]

This was extracted from #90408 in order to unblock work on converting sql_instances to an RBR table.

[ajwerner]

I just have nits, but I think this is also going to skew with #90875 which does some decoding.

Reviewed 6 of 7 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @jaylim-crl and @jeffswenson)

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 19 at r1 (raw file):

)

const sessionIDVersion = 1

nit: define a type which is a uint8 and then make this const that.

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pkg/sql/sqlliveness/slstorage/sessionid.go line 66 at r1 (raw file):

		return nil, b, nil
	}
	if len(b) < (uuid.Size + 3) {

nit: how do you feel about being pedantic with consts to explain it? Maybe something like:

const (
	legacyLen              = uuid.Size
	versionLen             = 1
	regionLengthLen        = 1
	minimumRegionLen       = 1
	minimumPrefixLen       = versionLen + regionLengthLen + minimumRegionLen
	minimumNonLegacyLen    = minimumPrefixLen + uuid.Size
)

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 72 at r1 (raw file):

	}

	// Decode the version

nit: period

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 79 at r1 (raw file):

	rest := b[2:]

	// Decode and validate the length of the region

nit: period

[jeffswenson]

In this case there was no skew, because the decoding is introduced by #90408.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @ajwerner and @jaylim-crl)

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pkg/sql/sqlliveness/slstorage/sessionid.go line 19 at r1 (raw file):

Previously, ajwerner wrote…

nit: define a type which is a uint8 and then make this const that.

Done

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 66 at r1 (raw file):

Previously, ajwerner wrote…

nit: how do you feel about being pedantic with consts to explain it? Maybe something like:

const (
	legacyLen              = uuid.Size
	versionLen             = 1
	regionLengthLen        = 1
	minimumRegionLen       = 1
	minimumPrefixLen       = versionLen + regionLengthLen + minimumRegionLen
	minimumNonLegacyLen    = minimumPrefixLen + uuid.Size
)

Done

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 72 at r1 (raw file):

Previously, ajwerner wrote…

nit: period

Done

---

pkg/sql/sqlliveness/slstorage/sessionid.go line 79 at r1 (raw file):

Previously, ajwerner wrote…

nit: period

Done

[ajwerner]

This pr makes me feel like having session ID defined as opaque bytes wasn't such a bad idea.

[jeffswenson]

bors r+

[craig]

Build succeeded:

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