We are not sure but all those requests from same IP with same query in such a few seconds gives us some confidence in this scenario.
I just opened a bug ticket: https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=15855 Attached to it is an extract of koha-opac-access_log for better understanding of the issue.
Also tested your code, works great on Chrome, IE11 and Firefox!
De : [hidden email] [mailto:[hidden email]] De la part de Frédéric Demians
Envoyé : jeudi 18 février 2016 09:14
À : SUZUKI Arthur
Cc : [hidden email]; [hidden email]; CROUZET Olivier; BOUIS Sonia
Objet : Re: [Koha-devel] Disabling multiple submission on search form
> Some impatient users tends to click several times on the “Go” button
> of the search form on OPAC. Probably in a desperate hope that this
> will speed up the whole process.
> However the result is quite opposite, as Zebra is then queried
> multiple times which increases the server cpu load, until it reach
> 100% and cause Denial of Service (boooh…)
Are you sure your users are doing that? Koha server can lag severely for other reasons...
> We had the idea of disabling the “searchsubmit” button upon first click.
> This is done by adding onclick=”this.disabled=true;” after “id=searchsubmit”
> in masthead.inc.