Using Large Lists

Question

In an Outlook AddIn I'm working on, I use a list to grab all the messages in the current folder, then process them, then save them. First, I create a list of all messages, then I create another list from the list of messages, then finally I create a third list of messages that need to be moved. Essentially, they are all copies of each other, and I made it this way to organize it. Would it increase performance if I used only one list? I thought lists were just references to the actual item.

Answer 1

Without seeing your code it is impossible to tell if you are creating copies of the list itself or copies of the reference to the list - the latter is preferable.

Another thing to consider is whether or not you could stream the messages from Outlook using an iterator block. By using a List<T> you are currently buffering the entire sequence of messages which means you must hold them all in memory, processing them one at a time. Streaming the messages would reduce the memory pressure on your application as you would only need to hold each message in memory long enough to process it.

Answer 2

Unless your lists contains 10 millions items or more, it should not be a problem.

Outlook seems to have a problem much smaller sized mailboxes, so I would say you are pretty much safe.