This is exactly what is being done here now.
If count in field less than 250 -> use list, instead - autocomplete.

Adam Armstrong wrote:
 I'd say we should supply a list when the field is below a certain
 size, else use auto complete.

 Sent from BlueMail <http://www.bluemail.me/r?b=9660>
 On 3 Jun 2017, at 13:19, Mike Stupalov <mike@observium.org
 <mailto:mike@observium.org>> wrote:

     Hi,

      please try with latest revision (r8611, db schema changed too).

     Some form fields will displayed as "input with autocomplete" instead "list".

     Johann Mallet wrote:

         Hello, I monitored very big network with great tool is
         Observium. But I have issue with "BGP All session" page : When
         I navigate on this page, the load time is >20 seconds. I have
         not the issue with "All ports" page. We have >22k BGP sessions
         and >1300 Remote ASN. The generation time displayed in bottom
         righ is between 1 and 2 sec. After some time, I think
         understand the problem : It's not generation issue, but
         navigator issue with javascript. The left pan load <0.5sec
         with first BGP list. But the right pan with search form load
15 seconds. The navigator freeze or greatly slowed down (with
         "warning : one onglet slowed navigator"). I have test with
         Firefox and Chrome : same result. I think the big list of
         "Remote AS" and "Peer address" place JS engine in crazy mode.
         Do you have option in configuration mode to disable the list
         of Remote AS/Peer address and only use free text? Or not
         charge all list and use JS to load list when an letter/number
         is provided? For the moment, we can't not really use this page
         :( Thank! Johann

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