feat(restore): Introduce incremental restore

[ahsanbarkati]

Incremental restore can be used to restore a set of incremental backups on a cluster with a part of the backup already restored.
No mutations should be made between a normal restore and an incremental restore.

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This change is 

[NamanJain8]

Looks good to me. Nice change. 🎉

One issue that we discussed regarding the stale predicates not getting deleted bcoz of predicate move.

[manishrjain]

Also compare the current manifest with the last manifest that was applied, and drop any predicates that have moved etc.

Secondly, use the incremental stream writer.

Reviewed 9 of 9 files at r1.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @ahsanbarkati)

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worker/draft.go, line 677 at r1 (raw file):

		defer closer.Done()

		glog.Infof("Got restore proposal at Index:%d, ReadTs:%d",

Index: <space> %d

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worker/online_restore.go, line 245 at r1 (raw file):

}

type IncrementalWriter struct {

Don't need this. We should ideally use incremental stream.

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worker/online_restore.go, line 350 at r1 (raw file):

		if mapRes.shouldDropAll {
			if err := pstore.DropAll(); err != nil {
				return errors.Wrap(err, "failed to reduce incremental restore map")

failed to drop all ...

[NamanJain8]

Few nit picks. Rest looks good.

[ahsanbarkati]

Reviewable status: 1 of 48 files reviewed, 4 unresolved discussions (waiting on @manishrjain and @NamanJain8)

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worker/draft.go, line 677 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Index: <space> %d

Done.

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worker/online_restore.go, line 245 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Don't need this. We should ideally use incremental stream.

Done.

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worker/online_restore.go, line 350 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

failed to drop all ...

Done.