From derby-dev-return-64780-apmail-db-derby-dev-archive=db.apache.org@db.apache.org Fri Nov 28 16:14:35 2008 Return-Path: Delivered-To: apmail-db-derby-dev-archive@www.apache.org Received: (qmail 4665 invoked from network); 28 Nov 2008 16:14:35 -0000 Received: from hermes.apache.org (HELO mail.apache.org) (140.211.11.2) by minotaur.apache.org with SMTP; 28 Nov 2008 16:14:35 -0000 Received: (qmail 98788 invoked by uid 500); 28 Nov 2008 16:14:46 -0000 Delivered-To: apmail-db-derby-dev-archive@db.apache.org Received: (qmail 98762 invoked by uid 500); 28 Nov 2008 16:14:46 -0000 Mailing-List: contact derby-dev-help@db.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: Delivered-To: mailing list derby-dev@db.apache.org Received: (qmail 98750 invoked by uid 99); 28 Nov 2008 16:14:46 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Fri, 28 Nov 2008 08:14:46 -0800 X-ASF-Spam-Status: No, hits=-2000.0 required=10.0 tests=ALL_TRUSTED X-Spam-Check-By: apache.org Received: from [140.211.11.140] (HELO brutus.apache.org) (140.211.11.140) by apache.org (qpsmtpd/0.29) with ESMTP; Fri, 28 Nov 2008 16:13:27 +0000 Received: from brutus (localhost [127.0.0.1]) by brutus.apache.org (Postfix) with ESMTP id 9EAFF234C2B0 for ; Fri, 28 Nov 2008 08:13:44 -0800 (PST) Message-ID: <1161043518.1227888824648.JavaMail.jira@brutus> Date: Fri, 28 Nov 2008 08:13:44 -0800 (PST) From: "Bryan Pendleton (JIRA)" To: derby-dev@db.apache.org Subject: [jira] Commented: (DERBY-2991) Index split deadlock In-Reply-To: <16734720.1186114252905.JavaMail.jira@brutus> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Virus-Checked: Checked by ClamAV on apache.org [ https://issues.apache.org/jira/browse/DERBY-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12651592#action_12651592 ] Bryan Pendleton commented on DERBY-2991: ---------------------------------------- Thanks for running the performance tests. It seems like the cases where you are seeing some performance problems are mostly those cases where the deadlocks were occurring. Since a small performance penalty is vastly superior to a deadlock, I think it would be reasonable to accept that penalty if the deadlocks are greatly reduced or (hopefully) eliminated. > Index split deadlock > -------------------- > > Key: DERBY-2991 > URL: https://issues.apache.org/jira/browse/DERBY-2991 > Project: Derby > Issue Type: Bug > Components: Store > Affects Versions: 10.2.2.0, 10.3.1.4 > Environment: Windows XP, Java 6 > Reporter: Bogdan Calmac > Assignee: Knut Anders Hatlen > Attachments: d2991-preview-1a.diff, d2991-preview-1a.stat, d2991-preview-1b.diff, d2991-preview-1b.stat, d2991-preview-1c.diff, d2991-preview-1c.stat, derby.log, InsertSelectDeadlock.java, Repro2991.java, stacktraces_during_deadlock.txt > > > After doing dome research on the mailing list, it appears that the index split deadlock is a known behaviour, so I will start by describing the theoretical problem first and then follow with the details of my test case. > If you have concurrent select and insert transactions on the same table, the observed locking behaviour is as follows: > - the select transaction acquires an S lock on the root block of the index and then waits for an S lock on some uncommitted row of the insert transaction > - the insert transaction acquires X locks on the inserted records and if it needs to do an index split creates a sub-transaction that tries to acquire an X lock on the root block of the index > In summary: INDEX LOCK followed by ROW LOCK + ROW LOCK followed by INDEX LOCK = deadlock > In the case of my project this is an important issue (lack of concurrency after being forced to use table level locking) and I would like to contribute to the project and fix this issue (if possible). I was wondering if someone that knows the code can give me a few pointers on the implications of this issue: > - Is this a limitation of the top-down algorithm used? > - Would fixing it require to use a bottom up algorithm for better concurrency (which is certainly non trivial)? > - Trying to break the circular locking above, I would first question why does the select transaction need to acquire (and hold) a lock on the root block of the index. Would it be possible to ensure the consistency of the select without locking the index? > ----- > The attached test (InsertSelectDeadlock.java) tries to simulate a typical data collection application, it consists of: > - an insert thread that inserts records in batch > - a select thread that 'processes' the records inserted by the other thread: 'select * from table where id > ?' > The derby log provides detail about the deadlock trace and stacktraces_during_deadlock.txt shows that the inser thread is doing an index split. > The test was run on 10.2.2.0 and 10.3.1.4 with identical behaviour. > Thanks, > Bogdan Calmac. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.