Hi,
Currently on a successful connection between protocol server and client,
the protocol client initiates a CHILD_UP event in the client stack. At
this point in time, only the connection between server and client is
established, and there is no guarantee that the server side stack is
ready to serve requests. It works fine now, as most server side
translators are not dependent on any other factors, before being able to
serve requests today and hence they are up by the time the client stack
translators receive the CHILD_UP (initiated by client handshake).
The gap here is exposed when certain server side translators like
NSR-Server for example, have a couple of protocol clients as their
child(connecting them to other bricks), and they can't really serve
requests till a quorum of their children are up. Hence these translators
*should* defer sending CHILD_UP till they have enough children up, and
the same CHILD_UP event needs to be propagated to the client stack
translators.
I have sent a patch(http://review.gluster.org/#/c/13549/) addressing
this, where we maintain a child_up variable in both the protocol client
and protocol server translators. The protocol server updates this value
based on the CHILD_UP and CHILD_DOWN events it receives from the
translators below it. On receiving such an event it forwards that event
to the client. The protocol client on receiving such an event forwards
it up the client stack, thereby letting the client translators correctly
know that the server is up and ready to serve.
The clients connecting later(long after a server has initialized and
processed it's CHILD_UP events), receive a child_up status as part of
the handshake, and based on the status of the server's child_up, either
propagate a CHILD_UP event or defer it.
Please have a look at the patch, and kindly state if it you have any
concerns or you foresee any scenarios of interest which we might have
missed.
Regards,
Avra
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