![]() If we cut ABe’s transaction into two independent transactions, then the server would be allowed to behave as if the order was:īut this is not a deadlock cycle – note the direction of arrows, they do not form a cycle! □Īlso, this picture depicts a violation of assumption that Write access to file A should be exclusive, as we can see two arrows going out of file A, so we have a contradiction with our assumptions. Remember that to achieve the promised serializability server has to come up with a convincing lie about the order of all transactions. Perhaps it is instructive to first answer a lingering question: Why can’t one of them simply release the Read access right as soon as they are done reading the first file and before requesting the Write access right for next file? For example, why not let ABe release his Read access right to file A, so that BAsil can obtain the Write access right to file A, finish his work, releasing all held access rights and thus letting ABe continue without any further delays? This would surely eliminate the deadlock, so why not do this seemingly smart thing? The short answer is: that would effectively be undistinguishable from cutting a transaction into two smaller ones, which might have surprising results. In InnoDB Data Locking – Part 1 “Introduction” we’ve seen a simple example of scenario in which two people can not finish what they’ve started, because one is waiting for the other to release a resource which is currently in use by the other and vice-versa: ABe already had Read access to file A and requested Write access to file B, but had to wait for BAsil to first release his Read access rights for this file, however BAsil can not do that until he finishes what he planned, which was to obtain Write access to file A, currently in use by ABe. Summary of this post: In this post I’ll describe how deadlock detection works in InnoDB 8.0.18, and thus introduce following concepts : deadlocks caused by granularity, and ways to overcome them by lock ordering.granularity of a lock (access right to everything vs.read views (read-only snapshots which allow stale reads concurrent to new writes).starvation (permanent inflow of readers starving a writer waiting for its turn).reader-writer lock (shared/exclusive access rights).timeouts (for misbehaving lock owners, and to resolve deadlocks).serializability of transactions (ability to explain states observed over time with a convincing story about relative order of parallel operations). ![]() databases, tables, rows (like files on a shared drive, spreadsheets inside a file, and rows inside a spreadsheet).In InnoDB Data Locking – Part 1 “Introduction” I’ve introduced basic concepts required to understand current post: Code: ERROR (.:1526): An error occurred in channel P_NLA_ADT_GW_IN (3df73330-2b02-4af2-bed5-92de82fe54f0) while processing message ID 13080 from the source queueĬom.data.DonkeyDaoException: .jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock try restarting transactionĪt .updateStatus(JdbcDao.java:722)Īt .executeTasks(BufferedDao.java:107)Īt .commit(BufferedDao.java:74)Īt .commit(BufferedDao.java:56)Īt .(Channel.java:1390)Īt .(Channel.java:1524)Īt .(Channel.java:1511)Īt (Thread.java:701)Caused by: .jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock try restarting transactionĪt 0(Native Method)Īt (NativeConstructorAccessorImpl.java:57)Īt (DelegatingConstructorAccessorImpl.java:45)Īt .newInstance(Constructor.java:534)Īt .handleNewInstance(Util.java:411)Īt .getInstance(Util.java:386)Īt .createSQLException(SQLError.java:1066)Īt .checkErrorPacket(MysqlIO.java:4187)Īt .checkErrorPacket(MysqlIO.java:4119)Īt .sendCommand(MysqlIO.java:2570)Īt .sqlQueryDirect(MysqlIO.java:2731)Īt .execSQL(ConnectionImpl.java:2815)Īt .executeInternal(PreparedStatement.java:2155)Īt .executeUpdate(PreparedStatement.java:2458)Īt .executeUpdate(PreparedStatement.java:2375)Īt .executeUpdate(PreparedStatement.java:2359)Īt .updateStatus(JdbcDao.In this blog series, I’m describing how InnoDB locks data (tables and rows) in order to provide illusion to clients that their queries are executed one after another, and how this was improved in recent releases.
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