Handle case of sequence number 0 files for compatibility with RocksDB.

[sumeerbhola]

Fixes #316

[petermattis]

This change is 

[petermattis]

modulo comment that somehow this scenario is happening in Pebble as well. Do you want me to dig into why?

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @ajkr, @itsbilal, @petermattis, and @sumeerbhola)

---

internal/manifest/version.go, line 461 at r1 (raw file):

		// in the file key intervals. This file is placed in L0 since it overlaps in the file
		// key intervals but since it has no overlapping data, it is assigned a sequence number
		// of 0 in RocksDB. We handle this case for compatibility with RocksDB.

#316 indicates that somehow Pebble is encountering this case as well. I'm not sure how, though.

[petermattis]

Do you want me to dig into why?

Seems to be a bug with range tombstones, and least in the case I'm looking at.

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @ajkr, @itsbilal, and @sumeerbhola)

[sumeerbhola]

thanks for looking. Should I hold off on submitting this?

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @ajkr, @itsbilal, and @sumeerbhola)

[petermattis]

No, this looks good to go. Still tracking down what is going on, but the search is now focused on flushable batches.

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @ajkr, @itsbilal, and @sumeerbhola)