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https://issues.apache.org/jira/browse/AMQ-7132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16740689#comment-16740689
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Christopher L. Shannon commented on AMQ-7132:
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[~alanprot] - I agree that it would be a separate patch but the more I think
about it the more I would say hold off for now...it's off by default so if we
store it in the index then that means we have to handle it conditionally always
which is kind of a pain or we need to always enable it which I don't want to
do. I don't think a lot of people care about the metrics and enabling it has
an extra performance cost as metrics get computed for each subscription on
every message add/remove etc
So for now I would say we can just leave your current patch as is and if there
is a need for it in the future we can create a new patch and add the
subscription stats to the index and bump the KahaDB version again as there is
no harm in having another version (ie version 8)
> ActiveMQ reads lots of index pages upon startup (after a graceful or
> ungraceful shutdown)
> -----------------------------------------------------------------------------------------
>
> Key: AMQ-7132
> URL: https://issues.apache.org/jira/browse/AMQ-7132
> Project: ActiveMQ
> Issue Type: Test
> Components: KahaDB
> Affects Versions: 5.15.8
> Reporter: Alan Protasio
> Priority: Major
> Fix For: 5.16.0, 5.15.9
>
>
> Hi.
> We noticed that ActiveMQ reads lots of pages in the index file when is
> starting up to recover the destinations statistics:
> [https://github.com/apache/activemq/blob/master/activemq-kahadb-store/src/main/java/org/apache/activemq/store/kahadb/KahaDBStore.java#L819]
> Nowadays, in order to do that, activemq traverse the
> storedDestination.locationIndex to get the messageCount and totalMessageSize
> of each destination. For destinations with lots of messages this process can
> take a while making the startup process take long time.
> In a case of a master-slave broker, this prevent the broker to fast failover
> and does not meet what is stated on
> [http://activemq.apache.org/shared-file-system-master-slave.html.]
> {quote}If you have a SAN or shared file system it can be used to provide
> _high availability_ such that if a broker is killed, another broker can take
> over immediately.
> {quote}
> One solution for this is keep track of the destination statistics summary in
> the index file and doing so, we dont need to read all the locationIndex on
> the start up.
> The code change proposed is backward compatible but need a bump on the kahadb
> version. If this information is not in the index, the broker will fall back
> to the current implementation, which means that the first time people upgrade
> to the new version, it will still have to read the locationIndex, but
> subsequent restarts will be fast.
> This change should have a negligible performance impact during normal
> activemq operation, as this change introduce a few more bytes of data to the
> index and this information will be on checkpoints. Also, this new information
> is synchronized with the locationIndex as they are update at the same
> transaction.
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