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From fredrikjonson <...@git.apache.org>
Subject [GitHub] activemq-artemis pull request: Change on buffer timeout...
Date Sun, 28 Jun 2015 11:43:38 GMT
Github user fredrikjonson commented on the pull request:

    https://github.com/apache/activemq-artemis/pull/54#issuecomment-116262734
  
    Clebert,
    
    First, perhaps you'll find the following phrasing clearer: "Timeout, in nanoseconds, after
which all journal buffer data is written to disk, regardless of amount of buffered data. Increasing
this value can improve message throughput at the cost increased latency." The phrasing was
inspired by the current user manual, http://activemq.apache.org/artemis/docs/1.0.0/persistence.html
    
    Second, I'm surprised by the proposed new value, 100 ns. I'm certain I must have misunderstood
either the unit (ns) or the current documentation of journal-buffer-timeout. The documentation
states that the attributes current "default for NIO is 3333333 nanoseconds - 300 times per
second, default for AIO is 500000 nanoseconds - ie. 2000 times per second." Is your intent
really to reduce this value several 1000 times, from 3333333 ns to 100 ns? Wouldn't that increase
the worst case IOPS requirement on the disk system from 2000 IOPS to 10000000(!) IOPS?
    
    Third, wouldn't it be better to change the default values in the source and let that change
be reflected by an update of the user manual (there are AFAIU two distinct values BTW, depending
on AOI or NIO), rather than changing a generated default configuration and thus letting the
default configuration diverge from the default value in the source code and the manual?


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