storage: renaming functions in the Reader interface

[sumeerbhola]

• Get to MVCCGet
• GetProto to MVCCGetProto
• Iterate to MVCCIterate
• ExportToSst to ExportMVCCToSst

Also added MVCCIterKind.

Release note: None

[cockroach-teamcity]

This change is 

[dt]

I'm not sure if we care, but ExportToSST isn't quite like the others in that it doesn't always do normal MVCC lastest-as-of-x reads, e.g. if revisions=true. Maybe it is still more MVCC-ish than not though?

[petermattis]

I don't have good thoughts on @dt's comment.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @dt, @itsbilal, @nvanbenschoten, @petermattis, and @sumeerbhola)

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pkg/storage/engine.go, line 636 at r5 (raw file):

// start (inclusive) and ending at end (non-inclusive).
// Specify max=0 for unbounded scans.
func Scan(reader Reader, start, end roachpb.Key, max int64) ([]MVCCKeyValue, error) {

This function is a bit dangerous, especially with max=0. Not for this PR, but I wonder if we should get rid of it. There are only 4 uses.

[sumeerbhola]

TFTRs!

I'm not sure if we care, but ExportToSST isn't quite like the others in that it doesn't always do normal MVCC lastest-as-of-x reads, e.g. if revisions=true. Maybe it is still more MVCC-ish than not though?

The use of "MVCC" in the naming here is saying that we are iterating over the part of the key space that can have multiple versions. Whether the caller is only interested in the latest version, or all, is orthogonal to this naming.

This is to distinguish it from iterating over the more general EngineKey key space which would include MVCC and lock table.

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @dt, @itsbilal, @nvanbenschoten, and @petermattis)

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pkg/storage/engine.go, line 636 at r5 (raw file):

Previously, petermattis (Peter Mattis) wrote…

This function is a bit dangerous, especially with max=0. Not for this PR, but I wonder if we should get rid of it. There are only 4 uses.

There are a lot of test uses (I see more than 20).

[sumeerbhola]

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)