Dejan Bosanac created AMQ-4495:
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Summary: Imporve cursor memory management
Key: AMQ-4495
URL: https://issues.apache.org/jira/browse/AMQ-4495
Project: ActiveMQ
Issue Type: Bug
Reporter: Dejan Bosanac
As currently stands, the store queue cursor will cache producer messages until
it gets to the 70% (high watermark) of its usage. After that caching stops and
messages goes only in store. When consumers comes, messages get dispatched to
it, but memory isn't released until they are acked. The problem is with the use
case where producer flow control is off and we have a prefetch large enough to
get all our messages from the cache. Then, basically the cursor gets empty and
as message acks release memory one by one, we go to the store and try to batch
one message at the time. You can guess that things start to be really slow at
that point.
The solution for this scenario is to wait with batching until we have more
space so that store access is optimized. We can do this by adding a new limit
(smaller then the high watermark) which will be used as the limit after which
we start filling cursor from the store again.
All this led us to the following questions:
1. Why do we use 70% as the limit (instead of 100%) when we stop caching
producer messages?
2. Would a solution that stop caching producer messages at 100% of usage and
then start batching messages from the store when usage drops below high
watermark value be enough. Of course, high watermark would be configurable, but
100% by default so we don't alter any behavior for regular use cases.
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