delete old 'Monitoring Agent' metrics and 'Automation Agent' Debug logs via scheduler
&gt;use mmsdbagentlog
switched to db mmsdbagentlog
&gt; show collections
app.agentLogs
&gt; db.app.agentLogs.stats()
{
    "ns" : "mmsdbagentlog.app.agentLogs",
    "count" : 1711298,
   "size" : 524287948,
    "avgObjSize" : 306,
    "storageSize" : 71323648,
    "capped" : true,
    "max" : -1,
    "maxSize" : 524288000,
    ... }


Looking in OpsManager Database , they use capped size collection to store the agent log , it seems we don't need to worry about the volume.
If the collection confuse you is not capped size , you could try to schedule a job with crontab in Linux(just an example) to remove those records :

db.collection.remove({_id : {$lt : ObjectId('55b0d1c40000000000000000')}})


first 8 character is hexadecimal timestamp can be generate in Linux Shell with command :

Today=`date +%F`
T=`date --date="$Today 00:00:00" +%s`
Stamp=`printf "%X" $T`''0000000000000000
echo $Stamp