From oracle-l-bounce@freelists.org Fri May 20 12:41:33 2005 Return-Path: Received: from air891.startdedicated.com (root@localhost) by orafaq.com (8.12.10/8.12.10) with ESMTP id j4KHfWGG012620 for ; Fri, 20 May 2005 12:41:32 -0500 X-ClientAddr: 206.53.239.180 Received: from turing.freelists.org (freelists-180.iquest.net [206.53.239.180]) by air891.startdedicated.com (8.12.10/8.12.10) with ESMTP id j4KHfV4Z012615 for ; Fri, 20 May 2005 12:41:32 -0500 Received: from localhost (localhost [127.0.0.1]) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTP id 2DF06195E19; Fri, 20 May 2005 11:38:27 -0500 (EST) Received: from turing.freelists.org ([127.0.0.1]) by localhost (turing [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 23646-05; Fri, 20 May 2005 11:38:27 -0500 (EST) Received: from turing (localhost [127.0.0.1]) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTP id A99EB194E5C; Fri, 20 May 2005 11:38:26 -0500 (EST) X-MimeOLE: Produced By Microsoft Exchange V6.0.6487.1 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Subject: RE: sequential read on full-table scan? Date: Fri, 20 May 2005 18:36:37 +0200 Message-ID: <7F0C000A3ABA6241A10C9ABF37EEB46D0A4A19@MSXVS01.trivadis.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: sequential read on full-table scan? Thread-Index: AcVdWIXtjzeaVzRITi6UKCC5I/peHAAASbfg From: "Christian Antognini" To: Cc: X-archive-position: 20020 X-ecartis-version: Ecartis v1.0.0 Sender: oracle-l-bounce@freelists.org Errors-To: oracle-l-bounce@freelists.org X-original-sender: Christian.Antognini@trivadis.com Precedence: normal Reply-To: Christian.Antognini@trivadis.com X-list: oracle-l X-Virus-Scanned: by amavisd-new-20030616-p9 (Debian) at avenirtech.net X-Spam-Level: X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on air891.startdedicated.com X-Spam-Status: No, hits=0.0 required=5.0 tests=AWL autolearn=ham version=2.63 Hi Paul >Why in the world would Oracle be reading a block at a time rather than >performing full-table scans? If Oracle recognizes that a single block has to be read, even while = executing a full table scan, it performs a db file sequential read. Three common situations lead to multi-block reads that are smaller than = the specified value: - Oracle reads headers with single-block reads - Oracle never does an I/O that spans more extents=20 - Oracle never reads a block that is already in the buffer cache HTH Chris -- http://www.freelists.org/webpage/oracle-l