source:azureus.aelitis.comReduce memory usage
From AzureusWiki
Since many users have trouble with excessive memory usage that's caused by Azureus here are some rules of thumb how to reduce the required memory size.
Note: Most settings require the advanced user mode
Get a current azureus version, they're usually more optimized than older ones
Update your Java version (preferably to the Sun JRE 1.5.0 Update 6)
disable every plugin you don't need under tools -> options -> plugins or even uninstall them via Plugins -> Uninstallation wizard. All plugins use up memory, especially the safepeer plugin which uses quite a bit. Instead of safepeer, it might be better to use an external IPblocker tool or at least use only one blocklist and not the "paranoid" set.
make sure you have good settings, esp. the number of connections and active torrents determines the memory usage since every peer connection and every running torrent creates management overhead.
Many users overestimate the importance of the number of peer connections since they think more peers = more download, but that's a misconception. Peers will only be willing to give data to you if you give data to them. Since your upload speed likely has a low cap, it is in your best interest to connect to only a few peers and send them as much data as possible, so they will reciprocate. More peers = more memory used + less available bandwidth due overhead of the BitTorrent protocol.
Generally 90-120 connections should be enough under most cicrumstances.
disable logging under tools -> options -> logging
remove unnecessary torrents, idle torrents still use some memory due to the information needed for queue management and the details display
set your disk cache size under Tools -> Options -> Files -> Performance Options to reasonable settings (4MB cache, 1MB read queue, 1MB write queue)
in case you have enabled the save peer connections feature under tools -> options -> files either disable it (not the Fast Resume mode) or set a reasonable limit... something that equals the number of peer max. connections.
make sure the built-in tracker is disabled by unchecking both Enable Tracker on ... options under tools -> options -> tracker -> server
disable the UPnP plugin and do manual port forwarding. Be careful, this could lead to trouble if it's not done correctly.
make sure the checkbox under Tools -> Options -> Plugins -> Distributed Tracker is set
create a link that calls Azureus.exe -J-Xmx64m to launch azureus with a JVM heap size that's restricted to 64MB
restart Azureus
This way I was able reduce Azureus' memory consumption from 142MB to 53MB and achieve CPU usage between 0 and 3 percent on a 2GHz machine.
They also have a guide for reducing CPU here.