Return-Path: X-Original-To: apmail-cassandra-user-archive@www.apache.org Delivered-To: apmail-cassandra-user-archive@www.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id 7DE0F4B87 for ; Wed, 13 Jul 2011 11:14:25 +0000 (UTC) Received: (qmail 40940 invoked by uid 500); 13 Jul 2011 11:14:22 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 40654 invoked by uid 500); 13 Jul 2011 11:14:15 -0000 Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: user@cassandra.apache.org Delivered-To: mailing list user@cassandra.apache.org Received: (qmail 40637 invoked by uid 99); 13 Jul 2011 11:14:13 -0000 Received: from nike.apache.org (HELO nike.apache.org) (192.87.106.230) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 13 Jul 2011 11:14:13 +0000 X-ASF-Spam-Status: No, hits=2.2 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_LOW,SPF_NEUTRAL X-Spam-Check-By: apache.org Received-SPF: neutral (nike.apache.org: local policy) Received: from [209.85.161.43] (HELO mail-fx0-f43.google.com) (209.85.161.43) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 13 Jul 2011 11:14:05 +0000 Received: by fxg17 with SMTP id 17so4889704fxg.30 for ; Wed, 13 Jul 2011 04:13:44 -0700 (PDT) MIME-Version: 1.0 Received: by 10.223.99.153 with SMTP id u25mr1507125fan.112.1310555623920; Wed, 13 Jul 2011 04:13:43 -0700 (PDT) Received: by 10.223.72.196 with HTTP; Wed, 13 Jul 2011 04:13:43 -0700 (PDT) In-Reply-To: References: Date: Wed, 13 Jul 2011 14:13:43 +0300 Message-ID: Subject: Re: Why do Digest Queries return hash instead of timestamp? From: David Boxenhorn To: user@cassandra.apache.org Content-Type: multipart/alternative; boundary=0015174beb466c131004a7f182b1 X-Virus-Checked: Checked by ClamAV on apache.org --0015174beb466c131004a7f182b1 Content-Type: text/plain; charset=ISO-8859-1 How would you know which data is correct, if they both have the same timestamp? On Wed, Jul 13, 2011 at 12:40 PM, Boris Yen wrote: > I can only say, "data" does matter, that is why the developers use hash > instead of timestamp. If hash value comes from other node is not a match, a > read repair would perform. so that correct data can be returned. > > > On Wed, Jul 13, 2011 at 5:08 PM, David Boxenhorn wrote: > >> If you have to pieces of data that are different but have the same >> timestamp, how can you resolve consistency? >> >> This is a pathological situation to begin with, why should you waste >> effort to (not) solve it? >> >> On Wed, Jul 13, 2011 at 12:05 PM, Boris Yen wrote: >> >>> I guess it is because the timestamp does not guarantee data consistency, >>> but hash does. >>> >>> Boris >>> >>> >>> On Wed, Jul 13, 2011 at 4:27 PM, David Boxenhorn wrote: >>> >>>> I just saw this >>>> >>>> http://wiki.apache.org/cassandra/DigestQueries >>>> >>>> and I was wondering why it returns a hash of the data. Wouldn't it be >>>> better and easier to return the timestamp? You don't really care what the >>>> data is, you only care whether it is more or less recent than another piece >>>> of data. >>>> >>> >>> >> > --0015174beb466c131004a7f182b1 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
How would you know which data is correct, if they both hav= e the same timestamp?

On Wed, Jul 13, 20= 11 at 12:40 PM, Boris Yen <yulinyen@gmail.com> wrote:
I can only say, "data" does matte= r, that is why the developers use hash instead of timestamp. If hash value = comes from other node is not a match, a read repair would perform. so that = correct data can be returned.=A0


On Wed, Jul 13, 2011 at 5:08 PM, David Boxen= horn <david@citypath.com> wrote:
If you have to pieces of data that are different but have = the same timestamp, how can you resolve consistency?

This is a path= ological situation to begin with, why should you waste effort to (not) solv= e it?

On Wed, Jul 13, 2011 at 12:05 PM, Boris Yen = <yulinyen@gmail.com> wrote:
I guess it is because the timestamp does not guarantee data consistency, bu= t hash does.

Boris


On Wed, Jul 13, 2011 at 4:= 27 PM, David Boxenhorn <david@citypath.com> wrote:
I just saw this

ht= tp://wiki.apache.org/cassandra/DigestQueries

and I was wondering why it returns a hash of the data. Wouldn't it = be better and easier to return the timestamp? You don't really care wha= t the data is, you only care whether it is more or less recent than another= piece of data.




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