Received: from localhost (maia-3.hub.org [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 9B2029FB4F2 for ; Tue, 27 Feb 2007 05:51:36 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-new, port 10024) with ESMTP id 52894-07 for ; Tue, 27 Feb 2007 05:51:29 -0400 (AST) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.4 Received: from ug-out-1314.google.com (ug-out-1314.google.com [66.249.92.174]) by postgresql.org (Postfix) with ESMTP id 6896C9FB4E1 for ; Tue, 27 Feb 2007 05:51:32 -0400 (AST) Received: by ug-out-1314.google.com with SMTP id k3so907375ugf for ; Tue, 27 Feb 2007 01:51:31 -0800 (PST) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:user-agent:mime-version:to:cc:subject:references:in-reply-to:content-type:content-transfer-encoding:sender; b=W6losyXiNTpaN33zF9Bo4O/jGAPJLmc69qpuQ9Y+m5HS7TQJT87O+EgdoaGlhov3vbUXbGgTbp1KVXhWK1bOTZVF9dkQqoIXaXHGXwBpZ2A+S+EvGr893fJD8RbTiPMGZJHl5y/hQYYfv4liCv/YZQx/doiqA4dJ78wyZOTrRsA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:user-agent:mime-version:to:cc:subject:references:in-reply-to:content-type:content-transfer-encoding:sender; b=RI9mAMOqVAHRKQ7tlCyTv58y0O8SUar8P2GcpckqcJQ0Mu1qjBAGMsxaxiFZRJ+4tphaTL4VRGO1sB6BPNXvLRnJHGIF2371wumXaVsfETCo7xt+NTh7KtqkwfBHL/B/2AoQbKK9Wsc3djhljlesKtTc8nWaOtRjHwVKnLf/IH0= Received: by 10.67.117.2 with SMTP id u2mr7739902ugm.1172569891044; Tue, 27 Feb 2007 01:51:31 -0800 (PST) Received: from ?172.24.32.72? ( [62.232.55.118]) by mx.google.com with ESMTP id y7sm7024888ugc.2007.02.27.01.51.27; Tue, 27 Feb 2007 01:51:29 -0800 (PST) Message-ID: <45E3FF0D.2050104@enterprisedb.com> Date: Tue, 27 Feb 2007 09:51:09 +0000 From: Heikki Linnakangas User-Agent: Icedove 1.5.0.8 (X11/20061116) MIME-Version: 1.0 To: Tom Lane CC: "Jim C. Nasby" , ITAGAKI Takahiro , pgsql-hackers@postgresql.org Subject: Re: Dead Space Map version 2 References: <20070227113655.6381.ITAGAKI.TAKAHIRO@oss.ntt.co.jp> <20070227051144.GK29041@nasby.net> <12631.1172555721@sss.pgh.pa.us> In-Reply-To: <12631.1172555721@sss.pgh.pa.us> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200702/1681 X-Sequence-Number: 99234 Tom Lane wrote: > The main problem with the levels proposed by Takahiro-san is that any > transition from FROZEN to not-FROZEN *must* be exactly recovered, > because vacuum will never visit an allegedly frozen page at all. This > appears to require WAL-logging DSM state changes, which is a pretty > serious performance hit. I doubt it would be a big performance hit. AFAICS, all the information needed to recover the DSM is already written to WAL, so it wouldn't need any new WAL records. > I'd be happier if the DSM content could be > treated as just a hint. I think that means not trusting it for whether > a page is frozen to the extent of not needing vacuum even for > wraparound. So I'm inclined to propose that there be only two states > (hence only one DSM bit per page): page needs vacuum for space recovery, > or not. Vacuum for XID wraparound would have to hit every page > regardless. If we don't have a frozen state, we can't use the DSM to implement index-only scans. Index-only scans will obviously require a lot more work than just the DSM, but I'd like to have a solution that enables it in the future. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com