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When committing or rolling back a transaction with HornetQ, the request to commit or rollback is sent to the server, and the call will block on the client side until a response has been received from the server that the commit or rollback was executed.
When the commit or rollback is received on the server, it will be committed to the
journal, and depending on the value of the parameter journal-sync-transactional
the server will ensure that the commit or
rollback is durably persisted to storage before sending the response back to the client.
If this parameter has the value false
then commit or rollback may not
actually get persisted to storage until some time after the response has been sent to
the client. In event of server failure this may mean the commit or rollback never gets
persisted to storage. The default value of this parameter is true
so
the client can be sure all transaction commits or rollbacks have been persisted to
storage by the time the call to commit or rollback returns.
Setting this parameter to false
can improve performance at the
expense of some loss of transaction durability.
This parameter is set in hornetq-configuration.xml
If you are sending messages to a server using a non transacted session, HornetQ can be configured to block the call to send until the message has definitely reached the server, and a response has been sent back to the client. This can be configured individually for durable and non-durable messages, and is determined by the following two parameters:
BlockOnDurableSend
. If this is set to true
then all calls to send for durable messages on non
transacted sessions will block until the message has reached the server, and a
response has been sent back. The default value is true
.
BlockOnNonDurableSend
. If this is set to true
then all calls to send for non-durable messages on non
transacted sessions will block until the message has reached the server, and a
response has been sent back. The default value is false
.
Setting block on sends to true
can reduce performance since each
send requires a network round trip before the next send can be performed. This means the
performance of sending messages will be limited by the network round trip time (RTT) of
your network, rather than the bandwidth of your network. For better performance we
recommend either batching many messages sends together in a transaction since with a
transactional session, only the commit / rollback blocks not every send, or, using
HornetQ's advanced asynchronous send acknowledgements feature
described in Section 20.4, “Asynchronous Send Acknowledgements”.
If you are using JMS and you're using the JMS service on the server to load your JMS
connection factory instances into JNDI then these parameters can be configured in
hornetq-jms.xml
using the elements block-on-durable-send
and block-on-non-durable-send
. If you're using JMS but not using JNDI then
you can set these values directly on the HornetQConnectionFactory
instance using the appropriate setter methods.
If you're using core you can set these values directly on the ClientSessionFactory
instance using the appropriate setter
methods.
When the server receives a message sent from a non transactional session, and that
message is durable and the message is routed to at least one durable queue, then the
server will persist the message in permanent storage. If the journal parameter journal-sync-non-transactional
is set to true
the
server will not send a response back to the client until the message has been persisted
and the server has a guarantee that the data has been persisted to disk. The default
value for this parameter is true
.
If you are acknowledging the delivery of a message at the client side using a non
transacted session, HornetQ can be configured to block the call to acknowledge until the
acknowledge has definitely reached the server, and a response has been sent back to the
client. This is configured with the parameter BlockOnAcknowledge
. If
this is set to true
then all calls to acknowledge on non transacted
sessions will block until the acknowledge has reached the server, and a response has
been sent back. You might want to set this to true
if you want to
implement a strict at most once delivery policy. The default value
is false
If you are using a non transacted session but want a guarantee that every message sent to the server has reached it, then, as discussed in Section 20.2, “Guarantees of Non Transactional Message Sends”, you can configure HornetQ to block the call to send until the server has received the message, persisted it and sent back a response. This works well but has a severe performance penalty - each call to send needs to block for at least the time of a network round trip (RTT) - the performance of sending is thus limited by the latency of the network, not limited by the network bandwidth.
Let's do a little bit of maths to see how severe that is. We'll consider a standard 1Gib ethernet network with a network round trip between the server and the client of 0.25 ms.
With a RTT of 0.25 ms, the client can send at most 1000/ 0.25 = 4000 messages per second if it blocks on each message send.
If each message is < 1500 bytes and a standard 1500 bytes MTU size is used on the network, then a 1GiB network has a theoretical upper limit of (1024 * 1024 * 1024 / 8) / 1500 = 89478 messages per second if messages are sent without blocking! These figures aren't an exact science but you can clearly see that being limited by network RTT can have serious effect on performance.
To remedy this, HornetQ provides an advanced new feature called asynchronous send acknowledgements. With this feature, HornetQ can be configured to send messages without blocking in one direction and asynchronously getting acknowledgement from the server that the messages were received in a separate stream. By de-coupling the send from the acknowledgement of the send, the system is not limited by the network RTT, but is limited by the network bandwidth. Consequently better throughput can be achieved than is possible using a blocking approach, while at the same time having absolute guarantees that messages have successfully reached the server.
The window size for send acknowledgements is determined by the confirmation-window-size parameter on the connection factory or client session factory. Please see Chapter 34, Client Reconnection and Session Reattachment for more info on this.
To use the feature using the core API, you implement the interface org.hornetq.api.core.client.SendAcknowledgementHandler
and set a handler
instance on your ClientSession
.
Then, you just send messages as normal using your ClientSession
, and as messages reach the server, the server will send
back an acknowledgement of the send asynchronously, and some time later you are
informed at the client side by HornetQ calling your handler's sendAcknowledged(ClientMessage message)
method, passing in a
reference to the message that was sent.
To enable asynchronous send acknowledgements you must make sure confirmation-window-size
is set to a positive integer value, e.g. 10MiB
Please see Section 11.1.59, “Send Acknowledgements” for a full working example.