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HBase >> mail # dev >> HBase replication: "in order semantics"


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Re: HBase replication: "in order semantics"
You are right on the last scenario. Deleted data might permanently resurface in that case.

HBASE-4721 is an attempt to deal with that (mostly a hack, IMHO).
-- Lars

________________________________
 From: Jan Van Besien <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Sent: Friday, November 16, 2012 3:18 AM
Subject: Re: HBase replication: "in order semantics"
 
On 11/15/2012 06:45 PM, lars hofhansl wrote:
> Yes. If there are failures in the source cluster the replicated data might be delivered out of order.

ok.

> Note that you will never see partial rows applied; replication will enforce HBase's ACID guarantee here,

ok.

> but rows might be delivered out of order, which means the ordering of deletes and puts might change, and hence lead to *temporary* visibility of deleted data. Eventually the state will be correct, though.

I understand that there are situations in which the reordering results in temporary visibility of deleted data. But additionally I also think that there are (unlikely) situations which can lead to permanent visibility of deleted data on the replica.

The situation I think of is:
- put followed by delete on source cluster
- reordering resulting in delete followed by put on replica
- delete gets executed on replica
- a major compaction happens on the replica (thus "really" deleting)
- put gets executed on the replica (thus permanently staying there)

Is there an error in my reasoning?

thanks,
Jan