Conference ulysse::rdb_vms_competition

No.

    I understand that only TANDEM NONSTOP/SQL is the closest to what we called
    a fully distributed database. And it costs megabucks I heard.
    
    
    Jeffrey

    Megabucks? NonStop SQL is included with the operating system. And yes,
    it's the only thing commercially available that is fully distributed.
    
    ---- Michael Booth

    Sybase and Interbase have some primitive support for 2PC.  They support
    a `prepare to commit' call as well as commit.  This allows the
    application to co-ordinate multiple transactions on multiple databases. 
    
    This isn't what real 2PC is about since there are miriad failure modes
    which the poor application programmer must deal with, most of which
    most of us would never dream of.  For example, what happens when all
    transactions have successfully completed the prepare to commit and the
    application has issued commits to every database but there is a failure
    somewhere which prevents one of the databases from committing.  When
    the error is corrected, the database should proceed to commit, not to
    rollback as you would expect.  Now, tell me how you handle that in an
    application.
    
    -mark

    Also Cognos Starbase has a 2PC protocol which must be similar to MArk's
    description in .-1 since it is based on either Sybase or Interbase.
    
    John.

    Re: .4, .5
    
    Wasn't Starbase previously called Interbase?  Or am I getting the
    various "bases" confused?
    
    As I recall, Rdb/ELN (the DSRI-compliant database for VAXELN) has a
    similar rudimentary two-phase commit -- a PREPARE statement is
    available.  (This should not come as a big surprise, given the origins
    of at least one third-party product.)  I think it maintains a sort of
    chain of record versions; this is how it does snapshots without using
    a snapshot file.  At some point, the latest version gets linked into
    the chain.  I've only seen an overview-y description (and that was some
    time ago), so I don't really know how the rollback worked, but it sure
    looked like most of the work of maintaining database integrity was left
    to the programmer.

    InterBase (aka StarBase) allows the program to attempt to commit a
    transaction that affects multiple databases. The problem is that should
    one of the updates fail, all that happens is a flag is raised in the
    database. The DBA must see the flag, then use the GFIX utility to
    manually bring the databases back in sync.
    
    Hardly state-of-the-art.
    
    ---- Michael Booth

    re.5 & .7
    
    COGNOS's marketing literature says that "their" database STARBASE
    has 2PC, however in a private discussion I had with one of their
    reps, he stated that they do not recommend their customers use this
    functionality for anything but very simple transactions, i.e. 2
    databases on the same machine.
    
    Michael

It's important to remember that applications do more than just database access.
Whatever else they do (file access, message sends, printing, whatever) should
also play in the 2PC arena.  So don't just treat 2PC as a simple YES/NO 
knock-off item on the database.  You need to ask:

1) Does the vendor supply a 2PC coordinator?  Or is the user expected to write
that?

2) What products (not just database) work with that coordinator?

and probably other questions, too.

    (Ever issued a ROLLBACK to the cash-dispenser?)