Comment 12 for bug 1818211

In my case, clamav is used for the mail traffic (amavis, postfix, dovecot) and the webproxy (squid over c-icap).
Hardware: Intel xeon, 24GB ECC-Ram, Raid5.
System: ArchLinux
After the update to clamav 0.100 it came to coredums and the accesses to the Internet over the squid-proxy became unbearably slow.
The following steps helped me to get the system working almost normally again. However, the system load on the CPU is considerably higher with clamav 0.100 than with clamav 0.99.4.
But at least I can now use the system again, without having to turn off the virus protection altogether. There are about 30 workstations on the system that use the mail server and the proxy.

Here are my steps:

1. Delete all signature databases that are located (in my case) under /var/lib/clamav.
2. Manual freshclam for the standard signatures
3. Setting default_dbs_rating="LOW" in /etc/clamav-unofficial-sigs/user.conf
4. Forcing reloading the signature databases with clamav-unofficial-sigs.sh -F

I use the following external sources:

sanesecurity_enabled = "yes"
securiteinfo_enabled = "yes"
linuxmalwaredetect_enabled = "yes"
malwarepatrol_enabled = "yes"
yararulesproject_enabled = "yes"
additional_enabled = "yes"

Maybe these steps will help you too.