I, myself have been having some weird problems regarding this since updating to Version 9.0.2011, with version 2010 Avastsvc.exe was using around 30-40MB on startup but shortly diminished to around 3-8MB average. After computer got through most of the lengthy processes (Windows Defender scans,etc) Avast would scan or read its dat/txt files and would go up to around 30-40MB again and drop just the same, while browsing the internet or watching videos, with each page refresh it'd jump to about 20MB and drop once again. Note that this is the Working Memory (KB) that I'm referring to, not the Commit (KB) that I find by using Window 7's Resource Monitor.
Ever since updating to the current version though Avastsvc uses 50-60MB Working (KB) from the get-go and around 75-80 Commit (KB), after the usual lengthy processes (see above) it dropped to around 60MB to 8, but then starts increasing over time, after browsing the internet for about an hour it rose to around 50MB once again and did not even attempt to drop or showed no signs of dropping. It only increases, while on version 2010 it constantly rose and dropped just as quickly, but theres no sign of this whatsoever now, it only rises and shows no signs that the shields are even working, even though they are. The increases/decreases in memory are generally the way of showing the shields are doing something I thought.
/sigh not sure whats going on but this is rather annoying, I'm rather OCD about the amount of memory my processes use and this drastic a change kind of bugs me. (maybe not a massive change in memory use but still it doesn't release the memory it seems and over time that can become a problem as I can leave my computer on for extended periods of time.)
I hope this gets fixed or some kind of explanation is given as to why it now is more RAM extensive.