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From "Pavel Moravec" <pmora...@redhat.com>
Subject Review Request 23305: [C++ broker] Make memory usage consistent after broker restart
Date Mon, 07 Jul 2014 16:59:53 GMT

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Review request for qpid, Gordon Sim and Kim van der Riet.

Summary (updated)

[C++ broker] Make memory usage consistent after broker restart

Bugs: QPID-5880

Repository: qpid

Description (updated)

Simple idea:
- in Queue::enqueue, set PersistableMessage::persistencyID "manually" to some unique number
that is identical to all message instances that has common SharedState - e.g. to the pointer
to SharedState
- during journal recovery, if we recover a message with already seen persistencyID, use the
previous seen instead with its SharedState and PersistableMessage bits

Known limitation:
- message annotations added to some queue (e.g. due to queue sequencing enabled) will be either
over-written or shared to all other queues during recovery

The patch contains a new QueueSettings option to enable (by default disabled) this feature
on per queue basis. This somehow limits the limitation above.

Isn't storing pointer to SharedState to the disk (via persistencyID) some sort of security
breach? (I dont think so, but worth to ask)

Can't manual setup of persistencyID break something in store? (AFAIK no as uniqueness of the
ID is assured: 1) a new / different message with the same persistencyID can appear only after
the previous instance is gone from memory, and 2) only queues with the option enabled are
checked for message coupling)

Will it help in cluster? No, it won't. As when primary broker gets 1 message to an exchange
that distributes it to 100 queues, th broker updates backup brokers via 100 individual "enqueue
1 message to queue q[1-100]" events. So backup brokers consume more memory than primary -
the same amount like primary does not share SharedState at all.

So it is reasonable for standalone brokers only.

Diffs (updated)

  /trunk/qpid/cpp/src/qpid/broker/Queue.cpp 1608083 
  /trunk/qpid/cpp/src/qpid/broker/QueueSettings.h 1608083 
  /trunk/qpid/cpp/src/qpid/broker/QueueSettings.cpp 1608083 
  /trunk/qpid/cpp/src/qpid/legacystore/MessageStoreImpl.h 1608083 
  /trunk/qpid/cpp/src/qpid/legacystore/MessageStoreImpl.cpp 1608083 
  /trunk/qpid/cpp/src/qpid/linearstore/MessageStoreImpl.h 1608083 
  /trunk/qpid/cpp/src/qpid/linearstore/MessageStoreImpl.cpp 1608083 

Diff: https://reviews.apache.org/r/23305/diff/

Testing (updated)

No significant difference in memory consumption before & after restart (in setup of 500
queues with qpid.store_msgID=true and thousands of messages sent via fanout exchange to all
of them).

Automated tests passed.


Pavel Moravec

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