You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@qpid.apache.org by "Robbie Gemmell (JIRA)" <ji...@apache.org> on 2011/03/24 23:07:05 UTC
[jira] [Updated] (QPID-3157) 'removed' subscriptions may be held in
memory by the queues SubscriptionList or 'lastSubscriptionNode' reference
[ https://issues.apache.org/jira/browse/QPID-3157?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Robbie Gemmell updated QPID-3157:
---------------------------------
Description:
subscriptions 'removed' from a queue subscription list are only marked deleted and can not actually bereleased from memory until the head of the subscription list advances beyond them. Additionally and perhaps more troublesome, a queues 'lastSubscriptionNode' can refer to a particular subscription but hold *all* subscequent subscriptions in memory whether they have been deleted or not and regardless whether the head of the SubscriptionList has advanced beyond them,
As a result any memory in use by the now-closed subscription will not be released until the queue is deleted, or all the subscriptions prior to it are closed and removed from the list *and* the 'lastSubscriptionNode' advances beyond them.. This also holds the associated ServerSession in memory, which is currently a rather heavyweight object.
This issue is further compounded when the queue has a backlog of messages and consumers are then created, used to recieve one message, and closed. In this scenario the broker sends the client as many messages as it can prefetch, leading to creation of up to <prefetch size, default=500> MessageTransfer commands, all which are recorded in the ServerSession but then left retained as 'unprocessed' in the closed session, which might be held in memory as described above. This results in an explosion in the number of MessageTransfer commands retained in memory as each message can have up to <prefetch size> MessageTransfer commands associated with it before it is eventually consumed by a client and all of thse will also be retained in memory by a 'removed' but not deleted subscription. The last effect can be combated by restricting the preftech size (eg appending &maxprefetch='1' to the connection url).
was:
subscriptions 'removed' from a queue subscription list are only marked deleted and not actually released from memory. As a result any memory in use by the now-closed subscription will not be released until the queue is deleted. This also holds the ServerSession in memory.
This issue compounded when the queue has a backlog of messages and consumers are created, used to recieve one message, and then closed. In this scenario the broker sends the client as many messages as it can prefetch, leading to creation of up to <prefetch size, default=500> MessageTransfer commands, all which are recorded in the ServerSession but then left retained as 'unprocessed' in the closed session. This results in an explosion in the number of MessageTransfer commands retained in memory as each message can have up to <prefetch size> MessageTransfer commands associated with it before it is eventually consumed by a client and all of thse will also be retained in memory. The last effect can be combated by restricting the preftech size (eg appending &maxprefetch='1' to the connection url).
Affects Version/s: 0.10
Fix Version/s: (was: 0.10)
0.11
Summary: 'removed' subscriptions may be held in memory by the queues SubscriptionList or 'lastSubscriptionNode' reference (was: subscriptions 'removed' from a queue subscription list are only marked deleted and not actually completely removed from the list)
Updating this with additional details from further analysis, and bumping out to 0.11: none of these issues are new to 0.10 (its been this way since time began apparently) and the number of aspects involved here make this too sensitive to introduce changes to so late in the 0.10 release process.
> 'removed' subscriptions may be held in memory by the queues SubscriptionList or 'lastSubscriptionNode' reference
> ----------------------------------------------------------------------------------------------------------------
>
> Key: QPID-3157
> URL: https://issues.apache.org/jira/browse/QPID-3157
> Project: Qpid
> Issue Type: Bug
> Components: Java Broker
> Affects Versions: 0.5, 0.6, 0.7, 0.8, 0.9, 0.10
> Reporter: Robbie Gemmell
> Priority: Blocker
> Fix For: 0.11
>
>
> subscriptions 'removed' from a queue subscription list are only marked deleted and can not actually bereleased from memory until the head of the subscription list advances beyond them. Additionally and perhaps more troublesome, a queues 'lastSubscriptionNode' can refer to a particular subscription but hold *all* subscequent subscriptions in memory whether they have been deleted or not and regardless whether the head of the SubscriptionList has advanced beyond them,
> As a result any memory in use by the now-closed subscription will not be released until the queue is deleted, or all the subscriptions prior to it are closed and removed from the list *and* the 'lastSubscriptionNode' advances beyond them.. This also holds the associated ServerSession in memory, which is currently a rather heavyweight object.
> This issue is further compounded when the queue has a backlog of messages and consumers are then created, used to recieve one message, and closed. In this scenario the broker sends the client as many messages as it can prefetch, leading to creation of up to <prefetch size, default=500> MessageTransfer commands, all which are recorded in the ServerSession but then left retained as 'unprocessed' in the closed session, which might be held in memory as described above. This results in an explosion in the number of MessageTransfer commands retained in memory as each message can have up to <prefetch size> MessageTransfer commands associated with it before it is eventually consumed by a client and all of thse will also be retained in memory by a 'removed' but not deleted subscription. The last effect can be combated by restricting the preftech size (eg appending &maxprefetch='1' to the connection url).
--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira
---------------------------------------------------------------------
Apache Qpid - AMQP Messaging Implementation
Project: http://qpid.apache.org
Use/Interact: mailto:dev-subscribe@qpid.apache.org