ivandika3 opened a new pull request, #9641:
URL: https://github.com/apache/ozone/pull/9641
## What changes were proposed in this pull request?
This task is to come up with the basic implementation of follower read
client proxy as a baseline before further performance improvements. The idea is
to simply pick a OM node in random (which be leader or follower / listener) and
use it to submit read requests. If the chosen OM node is a follower, the read
requests need to keep sending to that OM node unless the OM is down which
triggers failover. Write requests should be sent to the OM leader directly.
Further improvements such as followers priority or picking OM based on
latency, applied index, etc will be implemented in follow up tasks. The main
focus of this patch is to ensure that long-lived client can read from
followers. In the previous leader proxy provider implementation, the client
only read from followers until a new write request triggers
OMNotLeaderException and the failover causes proxy to always be pointing to the
leader.
The implementation is to introduce HadoopRpcOMFollowerReadProxyProvider
which wraps
HadoopRpcOMFailoverProxyProvider. FollowerReadProxyProvider tracks a
different currentOmNodeId from HadoopRpcOMFailoverProxyProvider.
FollowerReadInvocationHandler will check whether the request is a read request
(using OmUtils#isReadOnly) and if so forwards it to its current proxy. If it's
a write request, the request if forwarded to HadoopRpcOMFailoverProxyProvider
to be sent to the leader, which means that these clients do not utilize OM
followers as much as we want.
So the proxy hierarchy (each with its own InvocationHandler) is
- TracingUtil's proxy (InvocationHandler: TraceAllMethod)
- RetryProxy (InvocationHandler: RetryInvocationHandler)
- HadoopRpcOMFollowerReadProxyProvider (InvocationHandler:
FollowerReadInvocationHandler)
- ProtocolProxy (which is created in
OMFailoverProxyProviderBase#createOMProxy): ProtobufRpcEngine.Invoker
## What is the link to the Apache JIRA
https://issues.apache.org/jira/browse/HDDS-14379
## How was this patch tested?
UT and IT.
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