sync_log_chain - is it always needed?

[ellie timoney]

On Thu, Apr 30, 2020, at 12:29 AM, Olaf Frączyk wrote:
> However why the sync_log_chain could be not always active? As the server 
> catches all changes from LMTP, IMAP, POP anyway, why to use a special 
> option for the synchronization protocol? Why to treat replication 
> changes differently from LMTP/IMAP? If we want replication - we want to 
> catch all changes - regardless of the source, if we don't do replication 
> - we don't need to catch any changes.

The rolling sync_client takes care of cleaning up each sync_log file as it finishes replicating it downstream.

Now consider the case where your replica is an end point, not a link in a chain: it does not have a rolling sync_client forwarding replications on, so if it automatically logged incoming replications to the sync_log, the sync_log would simply grow forever and fill the disk.  You would need to set up a special job to delete it.... Better to simply not write it in the first place!

Thus, the default is to sync_log_chain: off, and if you need the special-case chaining behaviour, you turn it on.

Cheers,

ellie