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- Newsgroups: comp.databases
- Path: sparky!uunet!gatech!hubcap!ncrcae!ncr-sd!SanDiego.NCR.COM!robin!don
- From: don@robin.SanDiego.NCR.COM (Don.Russell)
- Subject: Re: Hot Standby DBMS's
- Message-ID: <1992Aug28.170456.12162@donner.SanDiego.NCR.COM>
- Summary: blocking 2-phase commit
- Keywords: X/Open, heuristic decisions
- Sender: news@donner.SanDiego.NCR.COM (News Owner)
- Reply-To: don@robin.SanDiego.NCR.COM (Don.Russell)
- Organization: NCR Corporation, Rancho Bernardo
- References: <1992Aug20.192538.17842@cbnewsl.cb.att.com> <BtB7Lo.26u@world.std.com> <1992Aug25.201150.22996@fig.citib.com> <BtLzB8.H9J@world.std.com>
- Date: Fri, 28 Aug 1992 17:04:56 GMT
- Lines: 40
-
- In article <BtLzB8.H9J@world.std.com> edwards@world.std.com (Jonathan Edwards) writes:
- >
- >Does the brokerage application makes changes to its own database as part
- >of a distributed transaction that includes changes in the requesting system?
- >If so, you have the well known problem that a 2-phase commit protocol can
- >block due to failure situations. This forces locks on one system to be held
- >till the other has recovered; manually breaking those locks can leave the
- >distributed transaction non-atomic: only parts of it completed. This is the
- >problem I was referring to.
- (stuff deleted)
- >
- >
- >
- >--
- >Jonathan Edwards edwards@intranet.com
- >IntraNet, Inc 617-527-7020
-
- X/Open allows for heuristic transaction completion. This could be a manual
- "breaking of locks". The resource manager (DBMS) is required to
- remember the heuristic decision. If the transaction coordinator times
- out the commit phase of the 2-phase commit, it tells the application
- that there is a heuristic hazard (possibility of non-atomic results).
- If the subordinate (broderage) takew a heuristic decision, it must
- remember it until told to forget it by the traansaction manager. When
- communications is restored between the two systems, recovery will
- cause the commit to finish properly (if the brokerage blocked or took
- a heuristic commit), or recovery will detect that the brokerage took
- the wrong decision -- in this case: heuristic rollback. At this
- point, an admiistrator can "fix" the problem.
-
- No patents are necessary here since it is covered by the X/Open XA
- Specification. TOP END is a transaction manager implementing the XA
- interface.
-
- Don Russell
- TOP END Distributed Transaction Management
- NCR Corporation
- San Diego, CA
-
- don.russell@SanDiegoCA.NCR.COM
-