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From lars hofhansl <la...@apache.org>
Subject Re: Disambiguate cell time for 1.0
Date Fri, 11 Apr 2014 03:22:00 GMT
Should we discuss this here: https://issues.apache.org/jira/browse/HBASE-10247?

 From: Sergey Shelukhin <sergey@hortonworks.com>
To: dev@hbase.apache.org 
Sent: Thursday, April 10, 2014 6:16 PM
Subject: Re: Disambiguate cell time for 1.0

Adding nonces to deletes and puts is possible, but it is overhead...

On Thu, Apr 10, 2014 at 6:16 PM, Sergey Shelukhin <sergey@hortonworks.com>wrote:

> Just to clarify what I was saying, there was a JIRA where we were
> discussing this.
> Server clocks are unreliable and when region moves (or if we have writable
> replicas) between-server clocks are even more sor.
> So we cannot really promise consistency wrt order even for requests from
> the same client now; even if we manage TS 100%.
> My suggestion was that we have 3 modes: (1) we manage TS on server => TS
> gets written as seqNum which has guarantees, no client-supplied TS; (2)
> client manages TS and supplies it, fail put if no TS; (3) legacy compat
> mode, but TS is generated in the client library instead of RS, so the onus
> is on the client app/client's server to manage clocks and there's no
> expectation that HBase will guarantee order.
> On Thu, Apr 10, 2014 at 5:09 PM, Nick Dimiduk <ndimiduk@gmail.com> wrote:
>> Reading through the write path, it seems to me that
>> RSRpcServices#doBatchOp(RegionActionResult.Builder,HRegion,List<Action>
>> mutations,CellScanner) should be honoring a nonce if present. The reason
>> being: if a client sends some Puts without specifying a TS, it relies on
>> the RS to provide one. Should such an operation succeed on the server but
>> the ACK not reach the client, client may resend the operation, silently
>> inserting more cells than intended. Deletes may well be a more sinister
>> issue, removing more cells than intended.
>> I've not yet written a test to confirm this.
>> There was conversation around the implementation of nonces discussing
>> options for removing the coupling of TS to clock-on-the-wall time. Sergey
>> describes the current situation quite eloquently: "server-generated TS
>> provide illusion of consistency guarantees which is not there by any
>> means". A fix for this will likely subtly break the semantics of our data
>> coordinates, and so should be addressed with 1.0, perhaps along side a
>> revamped client-side API.
>> -n

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