Avast used to scan very fast on my machine, around 4 and a half minutes for a full scan on the first scan and then under 2 minutes for any full scans after that. Recently running scans after the first doesn’t seem to gain any speed increases. I’ve not changed any settings in the program, did something change in one of the definition updates?
I tried deleting the persistent cache dat files and letting Avast re-create them but no change.
What does it mean “recently”?
Do you still have the old scans in Scan computer / Scan logs where you could find when exactly the runtime has changed?
I’d say within the last week, I don’t have any old scan logs sadly since I have them set to be kept for only 1 day, guess I should change that. Things are definitely scanning slower than they used to though.
Actually, I don’t understand the exact meaning of that.
The first scan is supposed to take longer, the subsequent ones should be faster. However, the “first scan” means “the first scan after installing avast!”, the “subsequent scans” means any scans after that.
Since I suppose you don’t reinstall avast! every day… what exactly do you mean by “first” and “any full scans after that”? The same Windows session (until Windows is restarted), or…?
And how long does it take now - 4.5 minutes any time (which is terribly fast, btw), or longer?
Sorry, I meant the first scan of the same Windows session takes around 4.5 minutes, if I then run a scan straight after it again takes around 4.5 minutes, where’s before the 2nd and any other full scans after the first in that Windows session would take less than 2 minutes due to the persistent cache, this no longer seems to be the case.
I realise 4.5 minutes is fast, I’m running a SSD. I only wonder if something is wrong because the scans are no longer getting faster like they used to. I have set the full scan to both populate the persistent cache and to use the persistent cache to speed up future scans.
If your system isn’t changing they won’t get beyond a certain time frame, it can’t possibly keep getting faster and faster until it disappears up it own back passage.
The Persistent cache doesn’t cater for ‘all files’ but only certain files which are guaranteed not to contain any virus infection (see below):
avast 5 - Scan Transient and Persistent caching to speed scanning.
Use transient caching - if transient caching is used, a file that has been scanned, and in which no infection was detected, will not be scanned again the next time it is accessed. However, this is only valid until the next virus definitions update, as the file may contain an infection that was not previously detected but which may be detected based on the new virus definitions. Also, information that the file is clean will only be stored in the computer's operating (temporary) memory. This means that when the system is restarted the information will be lost, therefore the file will also be scanned again the next time it is accessed after a system restart. This box is checked by default; if you want files to be scanned every time they are accessed. this box should be unchecked.Use persistent caching - if persistent caching is used, the information about the scanned file is stored in the permanent memory. This means it is not lost after a system restart and it is also not affected by virus definition updates. Consequently, persistent caching is suitable only for files which are guaranteed not to contain any virus infection e.g. operating system files, files signed by trusted publishers, or other files covered by the avast! whitelist. This box is checked by default; if you want all files to be scanned regardless of their trust status, this box should be unchecked.
Even files in the persistent cache must be checked to ensure they haven’t physically changed (whilst they aren’t scan if no change) so there is still a processing overhead.
I realise it won’t go beyond a certain time frame and I understand how the persistent cache works, I’m just stating that on my system, which hasn’t had any other changes other than the usual multiple times a day automatic definition updates from Avast, that scans are slower, as I said the first scan of a session would take around 4.5 minutes with any other scans after the first taking around 2.5 minutes or less, this is no longer the case. I’m just wondering if they changed something.
A large amount of the data on my system is music, videos and games, which shouldn’t need to be rescanned because those sorts of files aren’t changed often, so should scan a lot faster after the first scan of a session but this doesn’t seem to be the case.
Quick scans still seem to be working properly, first quick scan took 16 seconds, 2nd quick scan took 12 seconds.
could you send screen shots of your expert settings for “full scan”
1 performance tab
2 report file tab
thanks 
http://img401.imageshack.us/img401/8379/performancek.jpg
http://img683.imageshack.us/img683/5855/reportze.jpg
okay I suppose you didn’t change anything between the time you estimated that your scan times were short, and the time you started to find them too long…
What’s the amount of data that you’re scanning in a full scan (in GB)? (also, what’s your OS and SP?)
Nope, no settings changed at all.
I’m scanning around 212GB of data, though 109GB of that is videos, 5.8GB is music and 66GB is games which I’m guessing that most of those would be cached during the first scan so shouldn’t be fully scanned in any other scans during that Windows session.
I’m running Windows 7 Pro x64.
I don’t think this has anything to do with the persistent cache (which caches mainly executable files - certainly not videos and music).
The persistent cache is persistent - it holds the information accross reboots. So, it won’t cause the 2nd, 3rd, … scan in a Windows sessions to be faster - except for the very first scan after avast! has been installed, it affects all the following scans in the same way.
So, if the 2nd scan after you boot Windows is faster (than the first one right after the reboot), it most likely has something to do with Windows disk cache. It’s possible that now more data is read during the scan (either because you have a bit more data on your disk now, or maybe because the scanning engine now reads slightly more data than before, I don’t know; or, there more memory occupied now and the disk cache is smaller because of that) and it doesn’t fit into the Windows-allocated cache anymore (while it did previously, making the 2nd scan even faster).
the only thing I can tell is I’ve noticed on my system huge duration differences on a first full scan after an install from scratch, with identical settings, and no explanation so far…the difference I’m talking about here is like three times longer…This said following scans were equally short after any install.