Reading ResultSet from multiple threads

Question

Hello,

In the database, I have a definition table that is read from the application once upon starting. This definition table rarely changes, so it makes sense to read it once and restart the application every time it changes.

However, after the table is read (put into a ResultSet), it will be read by multiple handlers running in their own threads.

How do you suggest to accomplish this?

My idea was to populate a CachedRowSet, and then create a copy of this set (through the createCopy() method) for each handler every time a new request comes.

Do you think this is wise? Does this offer a good performance?

Thanks.

Answer 1

It may be better for you to use the singleton pattern. This would allow you to create a single class that all of your threads could access to get the object that they needed. This could also allow you to not have to shut down your application whenever changes are made. One way to accomplish this is to have a class where you have get and set methods for the information you need. And another class that will give out references of that object.

The class that gives out references could have a private constructor, and a getInstance method that will return a reference to itself to ensure that only one exists. This would also give you some other options regarding what you can do when things change.

Answer 2

Ok, if you control access to the resultSet, and you don't care to update the result set until you restart the application, then i would suggest wrapping the CachedRowSet in a custom class. One possible way to do this is to have a wrapper class that is a singleTon and provide it with getter methods so that other threads or classes for that matter can access it. That way you remove the need to make a copy and remove the dependency on CachedRowSet implementation. Creating a copy would cause unnessary overhead. Imagine, in the way you described above, if you had 1000 threads accessing your result set, you would call createCopy() 1000 times thus creating a 1000 copies of the same resultSet.

Answer 3

I think it is a pattern to read the configuration table into a static data structure (ConcurrentHashMap) and then let the threads to look it up.

You can ensure that there is no write race at startup by populating the reference map from a Servlet.init() - it is guaranteed to execute once per servlet.