Received: from maia.hub.org (maia-3.hub.org [200.46.204.243]) by mail.postgresql.org (Postfix) with ESMTP id 2C1DB1337B97 for ; Fri, 18 Mar 2011 10:31:04 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.243]) (amavisd-maia, port 10024) with ESMTP id 61881-08 for ; Fri, 18 Mar 2011 13:30:56 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-iy0-f174.google.com (mail-iy0-f174.google.com [209.85.210.174]) by mail.postgresql.org (Postfix) with ESMTP id E11651337B83 for ; Fri, 18 Mar 2011 10:30:55 -0300 (ADT) Received: by iyb26 with SMTP id 26so3979126iyb.19 for ; Fri, 18 Mar 2011 06:30:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=ovycO4RK9WYyOtF7VsCPLzf+wWd3YiIlHm8PUbYFEi4=; b=GFp2LWGwuGczj/0xqWQPR/v8LZMwaPcWxXdIUI7KYJ3rd2B15IjILhQ8aYq3icNUbk kRQCmqNdsVoLllqekhsJsRDUuxouptGqc0aofy4JweRcyZFHFEYreb4exNbwsPBwhwTW R3aKC44HmRcf4ylxfR/slKkW7+7VrGXP32wBY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=cty3pe7/Z6IP/WTkPEZ2IZTENEVnrD6pxvCtTdjwzCNbNy+P5Do/yfBYU+mx+0txX0 pY7RiMqkY55uaABZ/u2eDwN1oG1ygIw98DIIGSkVmq6HOsHq8Ox0LvG4NMAPxf+Qfj1F lPuDoBul2R7Lq6ZahNngwYczfi2asZqlD3QYs= MIME-Version: 1.0 Received: by 10.42.161.202 with SMTP id u10mr1634029icx.160.1300455056165; Fri, 18 Mar 2011 06:30:56 -0700 (PDT) Received: by 10.43.47.129 with HTTP; Fri, 18 Mar 2011 06:30:56 -0700 (PDT) In-Reply-To: References: <4D741441.2090704@dunslane.net> <1299454125.1696.6138.camel@ebony> <4D74896C.5030402@enterprisedb.com> <4D74DDFA.70800@dunslane.net> <4D74E584.7080409@enterprisedb.com> <4D74E9FA.7070202@dunslane.net> <4D74F3AE.9000802@dunslane.net> <4D74FDEC.5040406@enterprisedb.com> <4D74FF15.1070804@dunslane.net> <1299513979-sup-1987@alvh.no-ip.org> <4D832571.5030808@bluegap.ch> Date: Fri, 18 Mar 2011 09:30:56 -0400 Message-ID: Subject: Re: Re: [COMMITTERS] pgsql: Efficient transaction-controlled synchronous replication. From: Robert Haas To: MARK CALLAGHAN Cc: Markus Wanner , Alvaro Herrera , Andrew Dunstan , Heikki Linnakangas , Aidan Van Dyk , Simon Riggs , pgsql-hackers Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=1.72 tagged_above=-5 required=5 tests=BAYES_00=-1.9, FREEMAIL_FROM=0.001, FS_REPLICA=3.599, RCVD_IN_DNSWL_LOW=-0.7, SARE_SPEC_REPLICA=0.72 X-Spam-Level: * X-Archive-Number: 201103/1115 X-Sequence-Number: 184365 On Fri, Mar 18, 2011 at 9:16 AM, MARK CALLAGHAN wrote: > On Fri, Mar 18, 2011 at 9:27 AM, Markus Wanner wrote: >> Google invented the term "semi-syncronous" for something that's >> essentially the same that we have, now, I think. =A0However, I full >> heartedly hate that term (based on the reasoning that there's no >> semi-pregnant, either). > > We didn't invent the term, we just implemented something that Heikki > Tuuri briefly described, for example: > http://bugs.mysql.com/bug.php?id=3D7440 > > In the Google patch and official MySQL version, the sequence is: > 1) commit on master > 2) wait for slave to ack > 3) return to user > > After step 1 another user on the master can observe the commit and the > following is possible: > 1) commit on master > 2) other user observes that commit on master > 3) master blows up and a user observed a commit that never made it to a s= lave > > I do not think this sequence should be possible in a sync replication > system. But it is possible in what has been implemented for MySQL. > Thus it was named semi-sync rather than sync. Thanks for the insight. That can't happen with our implementation, I belie= ve. --=20 Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company