Details
Major Description
Our application FinanceCenter is based on Velocity as the template engine. We
have a library of about 200 macros and about 400 VM files. Because the
velocity parser copies the macro body into the VM during parsing, macros that
are frequently used (even though identical and using local contexts) use up
large amounts of memory. On our Linux server (running Redhat 7.2 with Sun JDK
1.4.1_04) we can easily use up over 1GB of RAM simply by opening up many forms
(about 150) - the server starts out using 60MB after startup. This memory
times out after 5 minutes and is returned which tells me that it is screen
memory. Our problem is that the NT JVM and Linux JVM (32 bit) are currently
limited to about 1.6 - 2.0 GB of ram for heap space. Thus, using a fair number
of forms in the application leaves little space for user session data.
We have implemented a caching mechanism for compiled templates and integrated
it into Velocity so that cached objects are timed out of the cache but the
server is still using large amounts of memory. We finally had to rewrite many
of our macros into Java so that memory usage would be reduced (note that these
macros were doing complex screen formatting not business logic). Doing this
has reduced our memory by about 30%. This is currently our biggest issue with
Velocity and is causing us to review our decision to stay with Velocity going
forward. This is because we will likely end up with close to 1,000 forms by
the end of next year and need to know that Velocity can deal with this. Is
there any work underway to share compiled macro AST's? This would greatly
reduce the amount of memory used. I have reviewed the parser code that is
doing this but it seems that this is an embedded part of the design and not
easily changed.
