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 214219FB2 for ; Mon, 13 Feb 2012 08:59:30 +0000 (UTC) Received: (qmail 94002 invoked by uid 500); 13 Feb 2012 08:59:27 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 93691 invoked by uid 500); 13 Feb 2012 08:59:14 -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 93679 invoked by uid 99); 13 Feb 2012 08:59:08 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Mon, 13 Feb 2012 08:59:08 +0000 X-ASF-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_MED,SPF_NEUTRAL X-Spam-Check-By: apache.org Received-SPF: neutral (athena.apache.org: local policy) Received: from [74.125.149.145] (HELO na3sys009aog121.obsmtp.com) (74.125.149.145) by apache.org (qpsmtpd/0.29) with SMTP; Mon, 13 Feb 2012 08:59:01 +0000 Received: from mail-lpp01m020-f173.google.com ([209.85.217.173]) (using TLSv1) by na3sys009aob121.postini.com ([74.125.148.12]) with SMTP ID DSNKTzjQvh1xdnSXOmqGHVVdz9z7BDaQuzvL@postini.com; Mon, 13 Feb 2012 00:58:41 PST Received: by lbbgf7 with SMTP id gf7so3109887lbb.18 for ; Mon, 13 Feb 2012 00:58:37 -0800 (PST) Received: by 10.152.148.106 with SMTP id tr10mr10741249lab.41.1329123517150; Mon, 13 Feb 2012 00:58:37 -0800 (PST) MIME-Version: 1.0 Received: by 10.112.26.199 with HTTP; Mon, 13 Feb 2012 00:58:17 -0800 (PST) In-Reply-To: References: <201202131403484201571@jike.com> From: Franc Carter Date: Mon, 13 Feb 2012 19:58:17 +1100 Message-ID: Subject: Re: keycache persisted to disk ? To: user@cassandra.apache.org Content-Type: multipart/alternative; boundary=e89a8f22c62f1a352904b8d4afe3 X-Gm-Message-State: ALoCoQk3vTqvjIG74Qh5ebcu3idCgOnb+P7iyqeTTzFzNIARPqPO3c6ssBFd3hVCNOxd5QTx1UMX --e89a8f22c62f1a352904b8d4afe3 Content-Type: text/plain; charset=ISO-8859-1 On Mon, Feb 13, 2012 at 7:49 PM, Peter Schuller wrote: > > I'm making an assumption . . . I don't yet know enough about cassandra > to > > prove they are in the cache. I have my keycache set to 2 million, and am > > only querying ~900,000 keys. so after the first time I'm assuming they > are > > in the cache. > > Note that the key cache only caches the index positions in the data > file, and not the actual data. The key cache will only ever eliminate > the I/O that would have been required to lookup the index entry; it > doesn't help to eliminate seeking to get the data (but as usual, it > may still be in the operating system page cache). > Yep - I haven't enabled row caches, my calculations at the moment indicate that the hit-ratio won't be great - but I'll be testing that later > > -- > / Peter Schuller (@scode, http://worldmodscode.wordpress.com) > -- *Franc Carter* | Systems architect | Sirca Ltd franc.carter@sirca.org.au | www.sirca.org.au Tel: +61 2 9236 9118 Level 9, 80 Clarence St, Sydney NSW 2000 PO Box H58, Australia Square, Sydney NSW 1215 --e89a8f22c62f1a352904b8d4afe3 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Mon, Feb 13, 2012 at 7:49 PM, Peter Schuller <peter.schuller@infidyne.com&g= t; wrote:
> I'm making an assumption . . . =A0I don't ye= t know enough about cassandra to
> prove they are in the cache. I have my keycache set to 2 million, and = am
> only querying ~900,000 keys. so after the first time I'm assuming = they are
> in the cache.

Note that the key cache only caches the index positions in the data file, and not the actual data. The key cache will only ever eliminate
the I/O that would have been required to lookup the index entry; it
doesn't help to eliminate seeking to get the data (but as usual, it
may still be in the operating system page cache).

=
Yep - I haven't enabled row caches, my calculations at the m= oment indicate that the hit-ratio won't be great - but I'll be test= ing that later
=A0

--
/ Peter Schuller (@scode, http://worldmodscode.wordpress.com)



--

Franc Carter<= /b> |<= /span> Systems architect | Sirca Ltd

franc.carter@sirca.org.au=A0|=A0www.sirca.org.au

Tel:= =A0+61 2 9236 9118

Level 9, 80 Clarence St, Sydney=A0NSW 2000

PO Box H58, Australia Square, Sydney NSW 1215<= /span>


--e89a8f22c62f1a352904b8d4afe3--