how can i record maximum amount of memory used over time in a linux server

I plan to launch an app, and plan to set its available memory optimistically high (it's a VPS). How can I figure out, say looking a month later, what it's maximum usage over that time was, i.e. if it ever came near to swapping memory? Thanks in advance for any feedback.

From serverfault Bill

• Install a munin server, and run a munin client on the virtual instance. It will log memory usage and a number of other useful statistists over time.

  From BillThor

• collectd is a plugin-based system statistics collection daemon. I believe the Memory plugin would fill the need.

  From Steven Monai

• There's the old standby, sar (sysstat/sa1). It can give you all sorts of useful statistics including memory and cpu utilization, disk io, etc. It's stable, run as a cronjob, and available for pretty much every linux distro.

  Bill : Thanks, that looks like just the ticket.
  From mark

• Another option would be running atop.

  From halp