From user-return-32383-apmail-cassandra-user-archive=cassandra.apache.org@cassandra.apache.org Mon Mar 4 21:02:19 2013 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 CC92DDFE0 for ; Mon, 4 Mar 2013 21:02:19 +0000 (UTC) Received: (qmail 9525 invoked by uid 500); 4 Mar 2013 21:02:17 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 9496 invoked by uid 500); 4 Mar 2013 21:02:17 -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 9488 invoked by uid 99); 4 Mar 2013 21:02:17 -0000 Received: from nike.apache.org (HELO nike.apache.org) (192.87.106.230) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 04 Mar 2013 21:02:17 +0000 X-ASF-Spam-Status: No, hits=2.9 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_NEUTRAL X-Spam-Check-By: apache.org Received-SPF: neutral (nike.apache.org: local policy) Received: from [206.225.165.119] (HELO HUB024-nj-4.exch024.serverdata.net) (206.225.165.119) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 04 Mar 2013 21:02:09 +0000 Received: from MBX024-E1-NJ-6.exch024.domain.local ([10.240.10.56]) by HUB024-NJ-4.exch024.domain.local ([10.240.10.39]) with mapi id 14.02.0318.001; Mon, 4 Mar 2013 13:01:48 -0800 From: Kanwar Sangha To: "user@cassandra.apache.org" Subject: RE: Replication Question Thread-Topic: Replication Question Thread-Index: Ac4ZGZavqYAClJ9/RiiW4MswcjUniQAActSg Date: Mon, 4 Mar 2013 21:01:47 +0000 Message-ID: <57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE39@mbx024-e1-nj-6.exch024.domain.local> References: <57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE24@mbx024-e1-nj-6.exch024.domain.local> In-Reply-To: <57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE24@mbx024-e1-nj-6.exch024.domain.local> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [38.122.186.90] Content-Type: multipart/alternative; boundary="_000_57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE39mbx024e1nj6exch_" MIME-Version: 1.0 X-Virus-Checked: Checked by ClamAV on apache.org --_000_57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE39mbx024e1nj6exch_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Keep in mind that even at consistency level ONE or LOCAL_QUORUM, the write = is still sent to all replicas for the written key, even replicas in other d= ata centers. The consistency level just determines how many replicas are re= quired to respond that they received the write. Is this true for Reads also ? From: Kanwar Sangha [mailto:kanwar@mavenir.com] Sent: 04 March 2013 14:54 To: user@cassandra.apache.org Subject: Replication Question Hi - If I configure a RF across 2 Data centres as below and assuming 3 nod= es per Data centre. DC1: 2, DC2:2 I do a write with consistency level - local_quorum which ensures that there= is no inter DC latency. Now say 2 nodes in DC1 crash and I am doing a read= with CL =3D One. Will it return failure to client since the data is now on= ly present in DC2 ? So I would need to do a read with CL =3D ALL/EACH_QUOR= UM to ensure that I always get the data even in case of crashes in the loca= l DC ? Thanks, Kanwar --_000_57C7C3CBDCB04F45A57AEC4CB21C0CCD1DB5EE39mbx024e1nj6exch_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Keep in mind that even at consistency level ONE or LOCAL_= QUORUM, the write is still sent to all replicas for the writt= en key, even replicas in other data centers. The consistency level just det= ermines how many replicas are required to respond that they received the write.

 

Is this true for Reads also ?

 

 

 

From: Kanwar S= angha [mailto:kanwar@mavenir.com]
Sent: 04 March 2013 14:54
To: user@cassandra.apache.org
Subject: Replication Question

 

Hi – If I configure a RF = across 2 Data centres as below  and assuming 3 nodes per Data centre.<= o:p>

 

DC1: 2, DC2:2

 

I do a write with consistency l= evel – local_quorum which ensures that there is no inter DC latency. = Now say 2 nodes in DC1 crash and I am doing a read with CL =3D One. Will it= return failure to client since the data is now only present in DC2 ? So  I would need to do a read with CL =3D A= LL/EACH_QUORUM to ensure that I always get the data even in case of crashes= in the local DC ?

 

Thanks,

Kanwar

 

 

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