nkeywal created HBASE-7590:
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Summary: Add a costless notifications mechanism from master to
regionservers & clients
Key: HBASE-7590
URL: https://issues.apache.org/jira/browse/HBASE-7590
Project: HBase
Issue Type: Bug
Components: Client, master, regionserver
Affects Versions: 0.96.0
Reporter: nkeywal
t would be very useful to add a mechanism to distribute some information to the
clients and regionservers. Especially It would be useful to know globally
(regionservers + clients apps) that some regionservers are dead. This would
allow:
- to lower the load on the system, without clients using staled information and
going on dead machines
- to make the recovery faster from a client point of view. It's common to use
large timeouts on the client side, so the client may need a lot of time before
declaring a region server dead and trying another one. If the client receives
the information separatly about a region server states, it can take the right
decision, and continue/stop to wait accordingly.
We can also send more information, for example instructions like 'slow down' to
instruct the client to increase the retries delay and so on.
Technically, the master could send this information. To lower the load on the
system, we should:
- have a multicast communication (i.e. the master does not have to connect to
all servers by tcp), with once packet every 10 seconds or so.
- receivers should not depend on this: if the information is available great.
If not, it should not break anything.
- it should be optional.
So at the end we would have a thread in the master sending a protobuf message
about the dead servers on a multicast socket. If the socket is not configured,
it does not do anything. On the client side, when we receive an information
that a node is dead, we refresh the cache about it.
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