Return-Path: X-Original-To: apmail-hadoop-hdfs-user-archive@minotaur.apache.org Delivered-To: apmail-hadoop-hdfs-user-archive@minotaur.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id 45F6ADB27 for ; Tue, 2 Oct 2012 23:13:59 +0000 (UTC) Received: (qmail 33244 invoked by uid 500); 2 Oct 2012 23:13:53 -0000 Delivered-To: apmail-hadoop-hdfs-user-archive@hadoop.apache.org Received: (qmail 33097 invoked by uid 500); 2 Oct 2012 23:13:53 -0000 Mailing-List: contact user-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: user@hadoop.apache.org Delivered-To: mailing list user@hadoop.apache.org Received: (qmail 33081 invoked by uid 99); 2 Oct 2012 23:13:53 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 02 Oct 2012 23:13:53 +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 (athena.apache.org: local policy) Received: from [209.85.223.176] (HELO mail-ie0-f176.google.com) (209.85.223.176) by apache.org (qpsmtpd/0.29) with ESMTP; Tue, 02 Oct 2012 23:13:42 +0000 Received: by ieak11 with SMTP id k11so19366602iea.35 for ; Tue, 02 Oct 2012 16:13:22 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type:x-gm-message-state; bh=zs6oipBjULAkJ4fcI3UETgP9byh8pBpKDrpkTaa6lk4=; b=CbjSaJpk2wOuPorwK+yDCuN9mbL0BwV477T5w1VLZktLpR0t5qNgg9+yPrGZRSyHw3 tr4cEOIVfw/ssuSBKMF9Z8gUfzGd1JDnaI4awIi0NfnugqRmVa16uxAd4b5ICysiNT3R dTMQ1zbcwyObcONKkuJnqQAwj+zSrIzNFQ0/rfQfWGsUy7t2Wq8TUe9KLQZkLs7dPBcB aUJpPD836YqOk+HJrHh1huOrJyc/s7coDsXpRNYYKyl0+eA+jD5HUd+9H+6anGJXlG3a 3JYQVZRo75bLbBEOOMATiwXu8XihPNUycyxLvHO2EaowQlzOjhSv0MLLAFByVfVwD14P /+og== Received: by 10.42.65.6 with SMTP id j6mr236324ici.2.1349219601758; Tue, 02 Oct 2012 16:13:21 -0700 (PDT) MIME-Version: 1.0 Received: by 10.64.39.102 with HTTP; Tue, 2 Oct 2012 16:13:01 -0700 (PDT) In-Reply-To: <029C75A3482BE64594E21FC09BB19F411385F342@BY2PRD0711MB428.namprd07.prod.outlook.com> References: <029C75A3482BE64594E21FC09BB19F411385F342@BY2PRD0711MB428.namprd07.prod.outlook.com> From: Ted Dunning Date: Wed, 3 Oct 2012 00:13:01 +0100 Message-ID: Subject: Re: HADOOP in Production To: user@hadoop.apache.org Content-Type: multipart/alternative; boundary=90e6ba6147741637da04cb1bab35 X-Gm-Message-State: ALoCoQkTr+bs7njKPq70Scn/J5CwmgHSw2Abbgb2sZHt8xf9v7J2tFGxGi8s0mZxGE4oxyR8TxGa X-Virus-Checked: Checked by ClamAV on apache.org --90e6ba6147741637da04cb1bab35 Content-Type: text/plain; charset=ISO-8859-1 On Tue, Oct 2, 2012 at 7:05 PM, Hank Cohen wrote: > There is an important difference between real time and real fast > > Real time means that system response must meet a fixed schedule. > Real fast just means sooner is better. > Good thought, but real-time can also include a fixed schedule and a specified list of exceptional conditions which would prevent meeting the schedule. It may also include a fixed schedule that must be met some fraction of the time (usually very near 100% of the time). Without providing exceptions, you basically force the designer to lie about how reliable their system is. > Real time systems always have hard schedules. The schedule could be in > microseconds to control a laser for making masks for semiconductor > manufacturing, milliseconds to control the ignition in your car or flight > controls on an F-22 or seconds for even slower moving processes. In real > time system missing the schedule can mean that very bad things happen: > planes fall from the sky, your laser printer fries it's imaging drum, > factories explode etc. > It can mean that. But if you specify the exceptional situations you can specifically mitigate for them. > Most transaction processing is happy with real fast > The folks doing high velocity trading are pretty close to real time but > they probably will be happy with real fast. > If real fast systems miss a schedule then someone loses money. > Yeah. And if you talk to these guys, they know the difference and ask for real-time. > The reason that RTOS type operating systems are popular for real time > applications is that they don't allow operations to spend indeterminate > amounts of time in uninterruptable states. Java will never qualify as a > real time system because it has garbage collection and garbage collection > can lock up a system for an indefinite amount of time while it goes through > marking and counting. > You are behind the times on a few counts. - Java's collectors don't "count". - Java can be real-time: http://rtjava.blogspot.co.uk/2009/07/real-time-java-vms.html - Garbage collection can be deterministic and real-time: http://www.ibm.com/developerworks/java/library/j-rtj4/index.html http://docs.oracle.com/cd/E13221_01/wlrt/docs30/intro_wlrt/tuning.html --90e6ba6147741637da04cb1bab35 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

On Tue, Oct 2, 2012 at 7:05 PM, Hank Coh= en <hank.cohen@altior.com> wrote:
There is an important difference between real time and real fast

Real time means that system response must meet a fixed schedule.
Real fast just means sooner is better.

= Good thought, but real-time can also include a fixed schedule and a specifi= ed list of exceptional conditions which would prevent meeting the schedule.=

It may also include a fixed schedule that must be met s= ome fraction of the time (usually very near 100% of the time).
Without providing exceptions, you basically force the designer= to lie about how reliable their system is. =A0
=A0
Real time systems always have = hard schedules. The schedule could be in microseconds to control a laser fo= r making masks for semiconductor manufacturing, milliseconds to control the= ignition in your car or flight controls on an F-22 or =A0seconds for even = slower moving processes. =A0In real time system missing the schedule can me= an that very bad things happen: planes fall from the sky, your laser printe= r fries it's imaging drum, factories explode etc.

It can mean that. =A0But if you specify th= e exceptional situations you can specifically mitigate for them.
= =A0
Most transaction processing is happy with real fast
The folks doing high velocity trading are pretty close to real time but the= y probably will be happy with real fast.
If real fast systems miss a schedule then someone loses money.

Yeah. =A0And if you talk to these guys, they know t= he difference and ask for real-time.

=A0
The reason that RTOS type operating systems are popular for real time appli= cations is that they don't allow operations to spend indeterminate amou= nts of time in uninterruptable states. =A0Java will never qualify as a real= time system because it has garbage collection and garbage collection can l= ock up a system for an indefinite amount of time while it goes through mark= ing and counting.

You are behind the times on a few counts.<= /div>

- Java's collectors don't "count"= ;.

- Java can be real-time:


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