Swan(sea) Song – personal research during my six years at Swansea ... and bey...
What is the difference between using private flow
1. What is the difference between
using private flow versus VM
transport?
2. • In this post, I will show the differences between chaining flows with
VM transport versus chaining flows with flow reference. When I need
to divide my Mule flows into reusable units, I often break them into
smaller flows and then chain them together in a main flow.
• Flows can be chained together using flow-refs or using VM
connectors; most recent examples use the flow-refs. However, flow-
refs are a Mule 3 addition and in Mule 2 VM connectors were used to
chain flows.
3. • Given this background and with flow-refs being more of the
recommended approach, is there a scenario when we would want to
use VM connectors? Yes, there is! But the majority of the time flow-
refs are preferred over the VM transport and here is why.
• * VM connector creates a transport barrier in the flow: In a transport
barrier, your Mule message goes through an entire serialization and
deserialization process which results in a new Mule message with the
same payload. Read about the effect of transport barrier on a mule
message here.
4. When one would prefer to use a VM
transport over a flow reference
• One case would be that VM endpoints enable message redelivery
strategies to be configured in your exception handling blocks – this is
not possible with flow-refs. VMs can do this because they internally
use a queue to hold messages while flow-refs are similar to simple
method calls.
5. • Look at the sample flow below; here the message will be redelivered
five times and is enabled by the use of VM inbound
6. • Contrast that to a private flow and chaining with flow-refs, if an
exception occurs in the called flow even though we have a rollback
strategy configured it will NOT execute because there is no internal
queue involved.
7.
8. • To summarize, don’t hesitate to use VM transports if you need
redelivery of messages. There are also differences in the use of thread
pools between private flows and VMs, but I will leave that for another
post. The sample source code for this post is available on Github.
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