From user-return-30461-apmail-cassandra-user-archive=cassandra.apache.org@cassandra.apache.org Tue Dec 4 19:53:06 2012 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 1696BD2C3 for ; Tue, 4 Dec 2012 19:53:06 +0000 (UTC) Received: (qmail 80726 invoked by uid 500); 4 Dec 2012 19:53:03 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 80699 invoked by uid 500); 4 Dec 2012 19:53:03 -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 80691 invoked by uid 99); 4 Dec 2012 19:53:03 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 04 Dec 2012 19:53:03 +0000 X-ASF-Spam-Status: No, hits=2.2 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_PASS X-Spam-Check-By: apache.org Received-SPF: pass (athena.apache.org: local policy) Received: from [208.113.200.5] (HELO homiemail-a43.g.dreamhost.com) (208.113.200.5) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 04 Dec 2012 19:52:57 +0000 Received: from homiemail-a43.g.dreamhost.com (localhost [127.0.0.1]) by homiemail-a43.g.dreamhost.com (Postfix) with ESMTP id A485D8C058 for ; Tue, 4 Dec 2012 11:52:54 -0800 (PST) Received: from [192.168.0.134] (unknown [116.90.132.105]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) (Authenticated sender: aaron@thelastpickle.com) by homiemail-a43.g.dreamhost.com (Postfix) with ESMTPSA id 2F3A78C057 for ; Tue, 4 Dec 2012 11:52:54 -0800 (PST) From: aaron morton Content-Type: multipart/alternative; boundary="Apple-Mail=_9E4C5633-CD46-4720-A28D-382B11667FD3" Message-Id: <81D05238-BD4C-46C4-AAAA-CD6A68CF7567@thelastpickle.com> Mime-Version: 1.0 (Mac OS X Mail 6.2 \(1499\)) Subject: Re: Help on MMap of SSTables Date: Wed, 5 Dec 2012 08:52:35 +1300 References: To: user@cassandra.apache.org In-Reply-To: X-Mailer: Apple Mail (2.1499) X-Virus-Checked: Checked by ClamAV on apache.org --Apple-Mail=_9E4C5633-CD46-4720-A28D-382B11667FD3 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=iso-8859-1 > Will MMapping data files be detrimental for reads, in this case? No.=20 > In general, when should we opt for MMap data files and what are the = factors that need special attention when enabling the same? mmapping is the default, so I would say use it until you have a reason = not to.=20 mmapping will map the entire file, but pages of data are read into = memory on demand and purged when space is needed.=20 Cheers ----------------- Aaron Morton Freelance Cassandra Developer New Zealand @aaronmorton http://www.thelastpickle.com On 4/12/2012, at 11:59 PM, Ravikumar Govindarajan = wrote: > Our current SSTable sizes are far greater than RAM. {150 Gigs of data, = 32GB RAM}. Currently we run with mlockall and mmap_index_only options = and don't experience swapping at all. >=20 > We use wide rows and size-tiered-compaction, so a given key will = definitely be spread across multiple sstables. Will MMapping data files = be detrimental for reads, in this case? >=20 > In general, when should we opt for MMap data files and what are the = factors that need special attention when enabling the same? >=20 > -- > Ravi --Apple-Mail=_9E4C5633-CD46-4720-A28D-382B11667FD3 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=iso-8859-1 Will MMapping data files be detrimental for = reads, in this case?No. 

In general, when should we opt for MMap data files and = what are the factors that need special attention when enabling the = same?
mmapping is the default, so I would say use it until = you have a reason not to. 

mmapping will map the = entire file, but pages of data are read into memory on demand and purged = when space is = needed. 

Cheers

http://www.thelastpickle.com

On 4/12/2012, at 11:59 PM, Ravikumar Govindarajan <ravikumar.govindarajan@gm= ail.com> wrote:

Our = current SSTable sizes are far greater than RAM. {150 Gigs of data, 32GB = RAM}. Currently we run with mlockall and mmap_index_only options and = don't experience swapping at all.

We use wide rows = and size-tiered-compaction, so a given key will definitely be spread = across multiple sstables. Will MMapping data files be detrimental for = reads, in this case?

In general, when should we opt for MMap data files = and what are the factors that need special attention when enabling the = same?

--
Ravi

= --Apple-Mail=_9E4C5633-CD46-4720-A28D-382B11667FD3--