Dedeepya created QPID-8546:
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Summary: Consumer falling behind producer in the BDB HA clusters
Key: QPID-8546
URL: https://issues.apache.org/jira/browse/QPID-8546
Project: Qpid
Issue Type: Bug
Components: Broker-J
Affects Versions: qpid-java-broker-8.0.5
Reporter: Dedeepya
With current Qpid Broker versions (up to 8.0.4 including) when BDB HA cluster
is distributed across different DCs, a consumer throughput falls significantly
behind the producer . As result, the total system throughput (determined by the
consumer) can be very low.
Such behavior is caused by implementation specifics of BDB message store:
* BDB HA transactions are synchronous for the majority of the nodes. (The
messaging transaction is committed when majority of the nodes in the cluster
acknowledge the transaction on their side)
* The deletion of dequeued messages from the store is synchronous and impacted
by the DC latency.
* 2 separate underlying store transactions are used to delete each individual
message data. Thus, if message consumption happens in transactional batches of
N, the messages are dequeued from the queue in the transacted batch of N
messages. However, after message dequeuing, the unreferenced message data is
deleted using its own store transactions (one for content and another for
metadata). As result for a batch of N, the store runs 1 + N*2 transactions. The
N*2 transactions are synchronous and executed one after another. If a latency
between data centers is high, it adds a corresponding delay to each store
transaction. As result, the message removal takes time. Only after deletion of
N messages, the broker sends commit confirmation to the client. The message
enqueing works differently.
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