Chu Cheng Li created HDDS-16737:
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Summary: Add a common base class for OM follower read proxy
providers
Key: HDDS-16737
URL: https://issues.apache.org/jira/browse/HDDS-16737
Project: Apache Ozone
Issue Type: Sub-task
Reporter: Chu Cheng Li
h3. Background
HDDS-15492 adds OM follower read to the gRPC client ({{GrpcOmTransport}}). The
S3 Gateway uses this client. HDDS-15089 adds a read consistency hint for each
request.
h3. Problem
The Hadoop RPC client keeps its follower read logic in
{{HadoopRpcOMFollowerReadFailoverProxyProvider}}. The gRPC client keeps a copy
of the same logic in {{GrpcOmTransport}}. Both copies contain:
* the follower read settings and the default read consistency hints,
* the check that decides if a request goes to a follower,
* the selection of the OM node for a follower read. For a {{LOCAL_LEASE}} read,
this selection skips the leader.
Thus, each change to follower read must be made in two places.
h3. Changes
* Add {{FollowerReadFailoverProxyProviderBase}}. It keeps the follower read
settings, the common helpers and the OM node selection.
* Make {{HadoopRpcOMFollowerReadFailoverProxyProvider}} extend the new base
class.
* Move the follower read logic from {{GrpcOmTransport}} to a new class
{{GrpcOMFollowerReadFailoverProxyProvider}}. This class also extends the base
class. {{GrpcOmTransport}} only sends the requests.
* Move {{OMFailoverProxyProviderBase#shouldUseFollowerRead}} to the base class.
h3. Tests
* Add {{TestFollowerReadFailoverProxyProviderBase}} and
{{TestGrpcOMFollowerReadFailoverProxyProvider}}.
* The existing follower read unit tests and integration tests pass without
change.
This change comes from a review comment on HDDS-15089:
https://github.com/apache/ozone/pull/11252#discussion_r4152973824
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