Christopher L. Shannon created AMQ-7136:
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Summary: Improve speed of KahaDB durable subscription pending
metrics recovery
Key: AMQ-7136
URL: https://issues.apache.org/jira/browse/AMQ-7136
Project: ActiveMQ
Issue Type: Improvement
Components: KahaDB
Affects Versions: 5.15.8
Reporter: Christopher L. Shannon
Assignee: Christopher L. Shannon
Fix For: 5.16.0, 5.15.9
There is a flag (off by default) in KahaDB to track pending metrics for durable
subscriptions. The recovery for the metrics requires iterating over the order
index for the topic on broker start in order to compute the pending message
size for each subscription. Currently this is done inefficiently because all
the messages that exist need to be iterated over for every subscription on the
Topic. The starting point of the iterating is where the subscriptions left off
so if there are many subscriptions with a lot of messages to consume this can
be very slow as the messages are iterated over several times.
A much better and faster way is to simply iterate over the messages one time
for the destination (starting at the first message that needs to be acked
across all subscriptions) and then adding the size to the counter for each
subscription where that message is pending.
Testing recovery on a Topic with a couple million messages and 10 durable
subscriptions has shown a pretty significant improvement in start up time of
KahaDB with this change (on my machine the recovery went down from 10+ seconds
to under 2 seconds)
Ultimately the fastest way to recover would be to write the pending metrics to
the index just like AMQ-7132 introduced for destinations but this is at least
an improvement over the current method without having to do another index
change. If we decide there is a need we can start writing the metrics to the
index in the same pattern as AMQ-7132 in a future update.
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