Return-Path: Delivered-To: apmail-cassandra-user-archive@www.apache.org Received: (qmail 80405 invoked from network); 18 Feb 2011 08:36:51 -0000 Received: from hermes.apache.org (HELO mail.apache.org) (140.211.11.3) by minotaur.apache.org with SMTP; 18 Feb 2011 08:36:51 -0000 Received: (qmail 77962 invoked by uid 500); 18 Feb 2011 08:36:48 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 77491 invoked by uid 500); 18 Feb 2011 08:36:45 -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 77477 invoked by uid 99); 18 Feb 2011 08:36:44 -0000 Received: from nike.apache.org (HELO nike.apache.org) (192.87.106.230) by apache.org (qpsmtpd/0.29) with ESMTP; Fri, 18 Feb 2011 08:36:44 +0000 X-ASF-Spam-Status: No, hits=1.5 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_LOW,SPF_PASS X-Spam-Check-By: apache.org Received-SPF: pass (nike.apache.org: domain of sylvain@datastax.com designates 74.125.83.44 as permitted sender) Received: from [74.125.83.44] (HELO mail-gw0-f44.google.com) (74.125.83.44) by apache.org (qpsmtpd/0.29) with ESMTP; Fri, 18 Feb 2011 08:36:35 +0000 Received: by gwb20 with SMTP id 20so1638868gwb.31 for ; Fri, 18 Feb 2011 00:36:13 -0800 (PST) MIME-Version: 1.0 Received: by 10.147.167.12 with SMTP id u12mr744717yao.13.1298018173738; Fri, 18 Feb 2011 00:36:13 -0800 (PST) Received: by 10.146.86.1 with HTTP; Fri, 18 Feb 2011 00:36:13 -0800 (PST) X-Originating-IP: [88.183.33.171] In-Reply-To: References: Date: Fri, 18 Feb 2011 09:36:13 +0100 Message-ID: Subject: Re: Frequent updates of freshly written columns From: Sylvain Lebresne To: user@cassandra.apache.org Cc: Aklin_81 Content-Type: multipart/alternative; boundary=20cf30433dec285e5b049c8a68a7 X-Virus-Checked: Checked by ClamAV on apache.org --20cf30433dec285e5b049c8a68a7 Content-Type: text/plain; charset=ISO-8859-1 On Fri, Feb 18, 2011 at 8:14 AM, Aklin_81 wrote: > Are the very freshly written columns to a row in memtables, efficiently > updated/overwritten by edited/new column values. > > After flushing of memtable, are those(edited + unedited ones) columns > stored together on disk (in same blocks!?) as if they were written in one > single operation or same time ?? I know if old columns are edited then > several copies of same column will be dispersed in different sst tables, > what about fresh columns ? > > Are there any disadvantages to frequently updating fresh columns present in > memtable ? > The SSTables are immutable but the memtable are not. As long as you update/overwrite a column that is still in memtable, it is simply replaced in memory (so it's as efficient as it gets). In other words, when the memtable is flushed, only the last version of the column goes in. -- Sylvain --20cf30433dec285e5b049c8a68a7 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Fri, Feb 18, 2011 at 8:14 AM, Aklin_81 <asdkl93@gmail.com> wrote:

Are the very freshly written columns to a row in memtables, efficiently upd= ated/overwritten by edited/new column values.

After flushing of mem= table, are those(edited + unedited ones) columns stored together on disk (i= n same blocks!?) as if they were written in one single operation or same ti= me ?? I know if old columns are edited then several copies of same column w= ill be dispersed in different sst tables, what about fresh columns ?

Are there any disadvantages to frequently updating fresh columns presen= t in memtable ?

The SSTables are immutable but the memtable are= not. As long as you update/overwrite a column that is still in memtable, i= t is simply replaced in memory (so it's as efficient as it gets).

In other words, when the memtable is flushed, only the last version of= the column goes in.=A0

Sylvain

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