functioner commented on a change in pull request #2878:
URL: https://github.com/apache/hadoop/pull/2878#discussion_r616213541
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File path:
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLogAsync.java
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@@ -378,13 +381,18 @@ public void logSyncWait() {
@Override
public void logSyncNotify(RuntimeException syncEx) {
- try {
- if (syncEx == null) {
- call.sendResponse();
- } else {
- call.abortResponse(syncEx);
+ for (int retries = 0; retries <= RESPONSE_SEND_RETRIES; retries++) {
Review comment:
@daryn-sharp Thanks for your explanation!
Now I understand that:
1. If the response cannot be sent it's either because the connection is
already closed or there's a bug preventing the encoding of the response.
2. If a speculated future bug left the connection open it's in an
unknown/inconsistent state with possible partial data written so writing
anything more is a corrupted or duplicate response for the client.
And I have more questions:
1. What kind of messages will be sent in this specific `call.sendResponse()`?
2. Among these messages, are there critical ones? I mean, maybe some
messages are important to the protocol and we don't want to lose them. If we
delegate them to a dedicated RPC thread/service/framework, the
disconnection/exception can be automatically handled so that those important
messages can reliably reach the receiver's side.
The `call.sendResponse()` is invoked after the edit log sync finishes, so
the transaction has been done. However, it swallows the possible exception so
it doesn't care whether it successfully replies (to datanode/client). Even if
we have the implication of disconnection in this scenario, I was wondering if
it's possible that a bug is hidden by this possibly ignored message? Thanks!
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