Re: Oracle replication wasRe: Sybase 11 TPCC on DEC (your comments please)

james.lawrence_at_epamail.epa.gov (Lawrence James) wrote:

>In article <1f7cc$c2716.d4_at_news> Matthew Houseman <mhouseman_at_arborsoft.com> writes:
 

>>isn't oracle replication simply PL/SQL? it may be easy to
>>use, but don't we all feel the need for speed for this sort
>>of technology?
 

>Yes it does use distributed transactions. Through the front door so to speak
>instead of through the back like sybase. Sybase should perform faster at the
>expense of a possible consistency problem. Oracle replicates the data and
>records that it has been successfully replicated as a single distributed
>commit. This ensures that it has been replicated.

I'm not sure what the implication is here - "front door", "back door".

The Sybase Replication System guarantees transaction delivery. Because transactions are applied to replicate databases in a fashion asynchronous to the primary database, there will be some latency between the time an update is seen in the primary data and replicate data. However, state consistency is achieved. That is, replicate databases will be in the same state that the primary was at an earlier point in time if not at the current point in time.

In comparing the Oracle strategy of a two-phased commit and Sybase's strategy of asynchronous commits we find advantages and disadvantages to both. Your particular implementation will probably dictate the best for you.

While with the two-phased commit strategy you can be sure that all replicate databases are consistent at any given time with the primary, performance does suffer and the possibility of transaction rollback at all sites increases with each replicate database entered into the system - if one replicate database is unavailable, the transaction fails at all sites.

With the asynchronous commit strategy, failure of one replicate database does not affect the primary database or any other replicate database. The transaction will be applied at the failing site once the database is back on-line, while all the other databases in the system committed the transaction as soon as it was received.