How can I force a out-of-date client to do a sync with master?

Question

I use 'DB_REPMGR_ACKS_NONE' for some clients which locate in different areas. But sometimes the network is not that good, and causes the client data out-of-date.
My question is that:
1. Is there a api that can do a manual sync without restarting the deamon? It seems 'DB_ENV->rep_sync' does not work. I know if I restart the client deamon, I can do it. But if I not?
2. If I continue to put lots of data on a master, it seems the client can catch up with master because I found that the 'next_lsn' of client is same with master. But if I only put some small data on a master, the 'next_lsn' of client still fall behind..Can you tell why?
Here's my environment:
Linux
db-4.6.21
using repmgr, not base api
Regards,
Steve

Answer 1

Hi Steve,
There is no API for on-demand synchronization with the master. The
rep_sync method is for something else. Please read about
"Synchronizing with a master":
    db-4.6.21/docs/ref/rep/mastersync.htmlThe only way to force resychronization on demand is to close the
environment and open it again.
A replication client checks the log sequence number of each incoming
log record, and can detect gaps in the sequence. If some log records
are lost due to network problems, then when later log records arrive
the client detects the missing records.
Generally the client will then request a new copy of the missing log
records from the master. However, it does not do so immediately,
because a perceived gap in the sequence of log records could instead
be nothing more than the fact that incoming log records can sometimes
be processed out of order. (Log record messages can also be
transmitted out of sequence in some network environments that don't
use TCP/IP -- but if you're using repmgr that is of course not the
case.)
Instead, the client waits for some number of out-of-sequence log
records before issuing the request for retransmission. One thing that
you can do is to tune the parameters governing this gap processing
algorithm. However, most users should not need to do this.
    db-4.6.21/docs/api_c/rep_request.htmlAlan Bram
Oracle