I've been having a problem that only sprouts up every 3 or 4 months, and usually right after a Zimbra version upgrade.

Amavasid causes high CPU and I have to restart the server. I've found that I get duplicate databases in /opt/zimbra/data/clamav/db/

-rw-r----- 1 zimbra zimbra 301568 Nov 17 05:06 bytecode.cld
-rw-r----- 1 zimbra zimbra 18213888 Nov 20 07:30 daily.cld
-rw-r----- 1 zimbra zimbra 6823191 Nov 20 15:35 daily.cvd
-r--r--r-- 1 zimbra zimbra 5360406 Aug 16 12:38 daily.cvd.init
-r--r----- 1 zimbra zimbra 30750647 Nov 20 15:30 main.cvd
-r--r--r-- 1 zimbra zimbra 30750647 Aug 16 12:38 main.cvd.init
-rw------- 1 zimbra zimbra 988 Nov 20 15:36 mirrors.dat

I'm able to fix this by running the following commands:
cd /opt/zimbra/data/clamav/db/
rm -rf *
/opt/zimbra/clamav/bin/freshclam --config-file=/opt/zimbra/conf/freshclam.conf -d --checks=12
zmamavisdctl stop
zmamavisdctl start
This basically deleted the existing ClamAV databases (which I believe are corrupt) and then Freshclam downloads new ones.
Restarting Amavisd fixes the problem.

What's weird is that when it first downloads the new databases, there is not a duplicate daily.* file. There is just the following:

-rw-r----- 1 zimbra zimbra 59212 Nov 20 16:39 bytecode.cvd
-rw-r----- 1 zimbra zimbra 6823485 Nov 20 16:39 daily.cvd
-rw-r----- 1 zimbra zimbra 30750647 Nov 20 16:34 main.cvd
-rw------- 1 zimbra zimbra 52 Nov 20 16:39 mirrors.dat

Any idea what is causing this problem?

I keep seeing this in the freshclam.log
[LibClamAV] Detected duplicate databases /opt/zimbra/data/clamav/db/daily.cvd and /opt/zimbra/data/clamav/db/daily.cld, please manually remove one of them