Re: 2-Phase commit or replication?
Date: 1995/06/01
Message-ID: <3qki4e$jut_at_caesar.ultra.net>#1/1
hharriso_at_tdc.dircon.co.uk (Henry Harrison) wrote:
>Mr Michael Wai Kee Yung (myung_at_hk.super.net) wrote:
>: Dear all, my company is running a 40-50 Gigabyte database using Oracle 7.
>: We're planning to set up a secondary site as the backup of our business
>: database. Could you all experts give me a clue what's the best solution
>: to implement this? I mean what's the pros and cons to use 2PC or
>: replication? Is 2PC a high performance penalty option? Would appreciate
>: if you can share with me your experience. Many thanks in advance.
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>Depends what you want, what your config is...Replication and 2PC are not
>really alternatives, they're two different ways of dealing with
>distributed databases (in fact, replication is implemented using 2PC).
>If you require complete consistency between the two databases you MUST
>use 2PC. If you just want to refresh the backup periodically, use
>replication.
>As to overhead of 2PC, this will mostly depend on the size and quality of
>the connection between the two sites.
>I personally wouldn't say that either 2PC OR Replication were exactly
>'tried and tested' technology (!) and I don't think I'd recommend them as
>a basis for backing up mission critical systems. If I remember rightly,
>Oracle's line is that this isn't what these technologies were designed for.
>You might like to look at some lower level mirroring schemes, though I
>don't know too much in this area.
>Henry Harrison
In a way of speaking 2PC and replication ARE the same thing.
Both guarantee consistency.
The difference is timing.
2PC gives immediate consistency.
Repication guarantees eventual convergence on consistency (assuming
no non-recoverable hard failure).
If immediate convergence is required then you need 2PC.
The down side is that if any node or link is down then everything is
down.
Replication avoids this and can be set up to converge very quickly if
the transaction rates are low but has severe band width problems.
Received on Thu Jun 01 1995 - 00:00:00 CEST