neils-dev commented on code in PR #3389:
URL: https://github.com/apache/ozone/pull/3389#discussion_r870552755
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hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/protocolPB/GrpcOmTransport.java:
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@@ -177,17 +181,22 @@ public void start() throws IOException {
public OMResponse submitRequest(OMRequest payload) throws IOException {
OMResponse resp = null;
boolean tryOtherHost = true;
+ int expectedFailoverCount = 0;
ResultCodes resultCode = ResultCodes.INTERNAL_ERROR;
while (tryOtherHost) {
tryOtherHost = false;
+ expectedFailoverCount = syncFailoverCount.get();
Review Comment:
Thanks @kerneltime for reviewing this PR and for your comments. The
`expectedFailoverCount` that is re-synced to the `syncFailoverCount` prior to
each` submitRequest` (over Grpc from s3g to om) and then checked against the
`syncFailoverCount `in the `shouldRetry` is to guard against another thread
also in failover incrementing the proxy index.
This is to ensure `performFailover` (of OmFailoverProxyProviderBase) " _is
supposed to called only once in a multithreaded enviornment. This is where the
failover occurs. performFailOver updates the currentProxyOmNode.._."
Implemented here, the `performFailover` is only applied in failover through
`shouldRety` iff `expectedFailoverCount` is in sync with the
`syncFailoverCount` (`expectedFailoverCount` == `syncFailoverCount`). Should
the `expectedFailoverCount` in `shouldRetry` method not equal the
`syncFailoverCount` at the point in failover, it implies that another thread is
in failover and has incremented the proxy to retry with. In this event the`
performFailover` is **_NOT_** called, instead the proxy is updated to the
current proxy index (which has been incremented by another thread in failover).
Please do check if the behavior of the failover with `performFailover` (in
`shouldRetry`) through the `expectedFailoverCount` and `syncFailoverCount` is
as we want it to be under multi-threaded environment.
```
if (syncFailoverCount.get() == expectedFailoverCount) {
omFailoverProxyProvider.performFailover(null);
syncFailoverCount.getAndIncrement();
} else {
LOG.warn("A failover has occurred since the start of current" +
" thread retry, NOT failover using current proxy");
}
```
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