On 5/3/12 2:54 PM, Josh Berkus wrote:
(2)  If logical transactions had been implemented as additions to
>  the WAL stream, and Slony was using that, do you think they would
>  still have been usable for this recovery?
Quite possibly not.

The key advantage that I see in londiste/slony replication is that your data 
stream has absolutely nothing to do with anything binary or internal to 
Postgres. That means that the only way corruption will travel from a master to 
a slave is if the corruption is in the actual fields being updated, and even 
that's not a given (ie: UPDATING a field to a completely new value would not 
propagate corruption even if the old value of the field was corrupted).

So, embedding a logical stream into WAL is not inherently bad... what would be bad is if 
that "logical" stream was susceptible to corruption due to something like full 
page writes. Simply embedding the exact same info slony or londiste captures into the WAL 
should be fine (though likely defeats the purpose). Translating binary WAL data into DML 
statements would very likely allow corruption to travel from master to slave.
Jim C. Nasby, Database Architect                   j...@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net

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