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From Emmanuel Lecharny <elecha...@gmail.com>
Subject [Mitosis] Push or pul, plus some random thoughts
Date Wed, 14 Jan 2009 22:54:27 GMT
Hi guys,

the current implementation of replication, AFAICT, is based on a pull 
system. So to speak, each time you modify some entry, a message is sent 
to all the replicas, waiting for an ack to be returned.

The main advantage is that we can't be faster: we replicate as soon as 
possible.

The main issue is that if a replica is not connected, we will try and 
try and try, until the remote server is back.

Here are some ideas I rehashed in the train on my way to office those 
last two days...

- We should ask the replicas to register to the other servers using a 
LDAP extended request
- then the server will push the modifications in a blocking queue for 
each replicas
- the blocking queue is read by a thread and the modifications are 
stored in a base, and sent to the replicas using a LDAP request, with a 
control (Replication)
- the replica receives the modifications as simple LDAP requests, plus a 
control, and deal with those, and send back a Ldap response with a 
status, allowing the modification to be removed from the store.
- if the replica is disconnected (for any reason), the server does not 
send anymore modifications to the replica, until the replica connects again.
- in this case, we simply restart the thread and send all the pending 
modifications found in the store and in the queue to the replica.

There are a few questions I still have to rehash :
- how many threads should we have ? A pool or one thread per replicas ?
- how do we manage the queue and the store ?
- when we reconnect, how do we tell the server which is the last entry 
correctly replicated ?
- and also how do we deal with reconnection if the server consider the 
replica is still connected ?

wdyt ?


-- 
--
cordialement, regards,
Emmanuel L├ęcharny
www.iktek.com
directory.apache.org



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