HBASE-30368 TableSnapshotScanner fails on an already restored MOB tab…

[liuxiaocs7]

…le snapshot

see: HBASE-30368

[Copilot]

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Pull request overview

This PR addresses failures in TableSnapshotScanner when scanning a snapshot that has been restored from a MOB-enabled table (HBASE-30368), by ensuring MOB “dummy” regions are excluded from scan region selection.

Changes:

• Add a new test that restores a MOB snapshot and verifies the scanner behaves correctly with a start row that yields no results.
• Update TableSnapshotScanner to filter out MOB region info entries when determining valid regions to scan.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestTableSnapshotScanner.java	Adds a regression test covering restored MOB snapshot scanning behavior.
hbase-server/src/main/java/org/apache/hadoop/hbase/client/TableSnapshotScanner.java	Excludes MOB dummy regions from isValidRegion to avoid attempting to open non-existent region dirs.

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[junegunn]

Thank you. The fix looks right to me.

I verified it locally: the test fails without the isValidRegion change, and a full scan of a restored mob snapshot still returns the real values, so skipping the pseudo-region does not lose data.

I have one request though. I realized the last clause of the comment ("holds no rows") is not accurate.

DefaultMobStoreFlusher appends the original cell to the mob file, then writes a reference cell to the normal store:

mobFileWriter.append(c);
...
// The key is same, the value is the filename of the mob file
ExtendedCell reference = MobUtils.createMobRefCell(c, fileName, ...);
writer.append(reference);

So the mob files do hold every row, with the real values. They just must not be scanned as a region, since they are reached by reference from the real regions. Simplest fix is to drop that clause:

Suggested change

	// The mob region is a dummy region used only to organise mob files under mobdir. It has no
	// region directory under the table dir to open, and holds no rows. See HBASE-30365 and
	// HBASE-30368.
	// The mob region is a dummy region used only to organise mob files under mobdir. It has no
	// region directory under the table dir to open. See HBASE-30365 and HBASE-30368.

That wording is mine from HBASE-30365, so the same clause is already on master in TableSnapshotInputFormatImpl. Could you fix that one in this PR too?

[liuxiaocs7]

Hi, @junegunn, thanks for catching this and for verifying the full scan. You're right—the “holds no rows” wording is inaccurate. I've removed it from both TableSnapshotScanner and TableSnapshotInputFormatImpl.