Re: TPC-A and -B Benchmarks

In <KGOR.93Jun26121035_at_aadt.aadt.com> kgor_at_aadt.aadt.com (Kent S. Gordon) writes:

>Can someone explain exactly what oracle discrete transactions are?

To quote from Section Q of some Oracle doc or other:

   Discrete transactions are useful for transactions that:

      o   modify only a few database blocks
      o   change each database block only once per transaction
      o   do not modify data likely to be requested by long-running queries
      o   do not need to see the old value of data before modifying the data

   During a discrete transaction, all changes made to any data are    deferred until the transaction commits. Redo information is    generated, but is stored in a separate location in memory. When the    transaction issues a commit request, the redo information is written    to the redo log file (along with other group commits) and the changes    to the database block are applied directly to the block. Then    control is returned to the application, once the commit completes.    This eliminates the need to generate undo information since the block    is not actually modified until the transaction is committed and the    redo information is stored in the redo log buffers.

In other words, all modified pages (and associated redo information) are locked in memory until commit time, and are unreadable by any transaction (including the originating discrete transaction). No rollback segment information is generated, so read-consistency is not maintained.

graeme

--
Disclaimer:	The author's opinions are his own, and not necessarily
		those of Pyramid Technology Ltd. or Pyramid Technology Inc.
---------------------------------------------------------------------------
      -m------- Graeme Sargent                 Voice: +44 (0)252 373035
    ---mmm----- Senior Database Consultant     Fax  : +44 (0)252 373135
  -----mmmmm--- Pyramid Technology Ltd.        Telex: Tell who???
-------mmmmmmm- Farnborough, Hants  GU14 7PL   Email: graeme_at_pyra.co.uk
---------------------------------------------------------------------------
    We have the technology.  The tricky bit is learning how to use it.