Re: Synchronization levels in SR

Dimitri Fontaine írta:
> Boszormenyi Zoltan <zb@cybertec.at> writes:
>   
>> Sorry for answering such an old mail, but what is the purpose of
>> a transaction level synchronous behaviour if async transactions
>> can be held back by a sync transaction?
>>     
>
> I don't understand why it would be the case (sync holding back async
> transactions) — it's been proposed that walsender could periodically
> feed back to the master the current WAL position received, synced and
> applied. 
>
> So you can register your sync transaction to wait (and block) until
> walsender sees a synced WAL position after your own (including it) and
> another transaction can wait until walsender sees a received WAL
> position after its own, for example. Of course, meanwhile, any async
> transaction would just commit without caring about slaves.
>   

The locks held by a transaction are released after
RecordTransactionCommit(), and waiting for the sync ack
happens in this function. Now what happens when a sync
transaction hold a lock that an async one is waiting for?

> Not implementing it nor thinking about how to implement it, it seems
> simple enough :)
>
> Regards,
>   


-- 
----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de    http://www.postgresql.at/