Why do spring/hibernate read-only database transactions run slower than read-write?

I've been doing some research around the performance of read-only versus read-write database transactions. The MySQL server is remote across a slow VPN link so it's easy for me to see differences between the transaction types. This is with connection pooling which I know is working based on comparing 1st versus 2nd JDBC calls.

When I configure the Spring AOP to use a read-only transaction on my DAO call, the calls are 30-40% _slower_ compared to read-write:

<!-- slower -->
<tx:method name="find*" read-only="true" propagation="REQUIRED" />
...
// slower
@Transaction(readOnly = true)

Versus:

<!-- faster -->
<tx:method name="find*" read-only="false" propagation="REQUIRED" />
...
// faster
@Transaction

Looking at tcpdump, it seems like the read-only transaction is doing more back and forth talking to MySQL. Here's the [read-only dump][1] versus [read-write][2].

1. Can anyone explain why the read-only calls are taking longer? Is this expected?

2. Is there anything I'm doing wrong or anything that I can do to improve their speed aside from improving the network? Just found this awesome post with some [good performance recommendations][3]. Any other comments?

Thanks much.

[1]:

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[2]:

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[3]:

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