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From "Christopher L. Shannon (JIRA)" <>
Subject [jira] [Commented] (AMQ-6477) ReduceMemoryFootprint should apply to non-persistent messages and subscriptions
Date Tue, 25 Oct 2016 13:34:58 GMT


Christopher L. Shannon commented on AMQ-6477:

[~gtully],  I've decided to be slightly more conservative for this patch.  I don't feel super
comfortable putting the memory clearing into the add method of the subscription like I did
in my original patch because we would get into a state where we have to unmarshall/marshal
the properties over and over again for each sub if there is a selector.  Plus there could
be race condition issues at that point since the message has now been handed off to the different
subscriptions.  So the new plan is to:

1) Still handle clearing the memory for non-persistent messages by checking if content and
marshalledProperties are not null (or if both marshalledProperties and properties are null)
2) For topics, move the clear memory method call from doMessageSend to the dispatch method
and put it after the subscriptionRecoveryPolicy check (which needs to use the properties and
triggers and unmarshal) but before the dispatch itself.

This will at least fix non-persistent messages and it will also clear memory for topic subscriptions
as long as there are no selectors (which is a less common case).  For the selector case where
the dispatch policy triggers an unmarshall I would need to think about it a bit more or maybe
we'd just need to do something like you mentioned earlier where we actually count the size
of both objects in memory.

> ReduceMemoryFootprint should apply to non-persistent messages and subscriptions
> -------------------------------------------------------------------------------
>                 Key: AMQ-6477
>                 URL:
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.14.1
>            Reporter: Christopher L. Shannon
>            Assignee: Christopher L. Shannon
> There is a flag called reduceMemoryFootprint which will clear out the unmarshalled state
of a message after it is added to a queue/topic because that state isn't counted towards the
size and can lead to OOM errors.
> However, even setting this flag, I am still seeing some brokers run out of memory.  After
analyzing the heap dumps I have found 2 reasons for this:
> 1) Non-persistent messages do not have their unmarshalled state cleared.  This was done
because when a message is persisted it is guaranteed to have the marshalled state.  However
we can still clear the memory for non-persistent messages as long as we check to make sure
the marshalled state exists first, which it will for transports like TCP but won't exist for
the VM transport.
> 2) When a message is added to a subscription the properties are needed to check which
subscription messages can be dispatched to.  This causes the memory to be unmarshalled again.
> In the topic case, we should probably defer the clearing of the state until after the
message is added to a subscription because messages are immediately dispatched to topic subs
so we don't unnecessarily have to convert the data twice.  In the queue case it probably makes
sense to clear memory on add to the queue and on add to the subscription.

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