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https://issues.apache.org/jira/browse/JAMES-3613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17380388#comment-17380388
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Benoit Tellier commented on JAMES-3613:
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To be noted: this MDC context is re-computed for *each and every message*
leading to one DNS resolution per message received...
Which likely means the above specified limit could be hit with just a few big
messages and no JVM local DNS cache.
I bet we should rather :
- Compute the MDC builder upon establishing the connection
- Save it as a netty connection attachment
- reuse it for follow up messages...
This would prevent multiple MDC recomputation and should be fixing the issue
too.
> Avoid DNS resolution for protocol MDC context
> ---------------------------------------------
>
> Key: JAMES-3613
> URL: https://issues.apache.org/jira/browse/JAMES-3613
> Project: James Server
> Issue Type: Improvement
> Components: IMAPServer, POP3Server, SMTPServer
> Affects Versions: 3.4.0, 3.5.0, 3.6.0
> Reporter: Benoit Tellier
> Priority: Major
> Fix For: 3.7.0
>
>
> On gitter: {code:java}
> Running into an odd issue after an application restart. (James 3.4.0 running
> in SpringBoot application). Was working fine, but now seem to be getting
> hung, or at least slow threads, on java.net.Inet6AddressImpl.getHostByAddr as
> called by
> org.apache.james.protocols.netty.ProtocolMDCContext.retrieveHost(ProtocolMDCContext.java:55).
> My environment is Java 11, on Amazon Linux 2, on EC2.
> {code}
> https://gist.github.com/devondragon/8ec7424a48dc843338443b0b98356289
> this seems to have been caused by too many incoming SMTP connections. Showed
> up in an odd way, but by decreasing the inbound connections this issue has
> stopped happening...
> Likely some rate limit on DNS resolution.
> Proposal: switch from `getHostName` to `getHostString` to prevent the DNS
> resolution.
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