When doing a Quick Scan or Full Scan, there is the option to “store data about scanned files in the persistent cache” which slows the scan. What are the benefits of doing this? Are there any draw back?
Thanks
Hi:
If I understand the process correctly choosing “store data about scanned files in the persistent cache” will result in the initial scan taking longer; BUT then subsequent scans are quicker. 
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.
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.
Thanks for the explanations.
It appears that in the Real Time settings that both the Transient and Persistent boxes are checked by default.
My question pertained to the setting for on demand scans (quick and full) where it asks if you want to “Store data about scanned files in the Persistent Cache which will slow the scan”. This is unchecked by default. What are the pros and cons of checking it?
Thanks
You’re welcome.
Yes, but the “store data about scanned files in the persistent cache” option in on-demand scans (if you use them) aren’t enabled by default.
The pros and cons are essentially in the information already given, initially it will slightly slow a scan as it records this information, but speed up future scans as those files eligible for the persistent scan don’t need to be scanned if they haven’t changed.
Thanks again, David.
So I assume that they are safe to use and don’t compromise your security, since Avast makes the decision of which types of file the pass over in future scans. Is this right?
They wouldn’t be there if they weren’t safe, there shouldn’t be any compromise if the file is changed it is automatically scanned as it no longer matches the file that was in the persistent cache.
Avast makes the decision on what files are considered ‘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.’ to be included in the Persistent cache. I have no doubt to get added to that list is no easy task.
This is good to know.
Thanks again for the help.
No problem, glad I could help.