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From "Alan Conway (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PROTON-1408) long-lived connections suffer large performance hit after many messages
Date Tue, 28 Mar 2017 00:24:42 GMT

    [ https://issues.apache.org/jira/browse/PROTON-1408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15944294#comment-15944294

Alan Conway commented on PROTON-1408:

How about we introduce an explicit `uintptr_t  pn_sequence_hashcode(pn_sequence_t n)` For
now it can use the  implementation proposed above. It is very likely that  a good hash function
for sequence numbers is NOT the same as a good hash function for void* pointers, so an explicit
hash function would give us a place to put a better algorithm if we ever get to that.

I haven't  found the culprit but different conversion sequences from int32_t via void*/uintptr_t
could give different results. The C integer conversion rules for uintptr = int32 require sign
extension, but casting int32 to void* and *then* assigning to uintptr would give a bit copy
- which is almost certainly not the same if uintptr_t is 64 bits. So if we have slightly different
code paths it could give inconsistent results. An explicit hash function that takes a pn_sequence_t
will ensure there is only one way to do the conversion and is self-explanatory.

> long-lived connections suffer large performance hit after many messages
> -----------------------------------------------------------------------
>                 Key: PROTON-1408
>                 URL: https://issues.apache.org/jira/browse/PROTON-1408
>             Project: Qpid Proton
>          Issue Type: Bug
>          Components: proton-c
>            Reporter: michael goulish
>            Assignee: Alan Conway
>         Attachments: jira_proton_1408_reproducer.tar.gz
> In long-running soak tests, in which connections are never taken down, I am seeing a
sudden & severe performance degradation when the number of messages over the connection
reaches about 6.4 billion.  
> This is happening in tests with two senders, two receivers & one router intermediating.
> I have tried C libUV clients as well as CPP clients.  Behavior is not identical, but
I see sudden performance drop, ie. 8x throughput decrease or worse, in both cases.
> Alan / Ted / Ken see an issue in use of improper comparison logic in pn_do_disposition(),
in transport.c  .     I am trying to prove this now.

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