[Koha] OPAC Search too slow in Koha 18.05.05

[Camilo Freire]

Good afternoon. My name is Camilo Freire, from Montevideo, Uruguay.

I have a catalogue with around 280.000 bibliographic records in Koha
18.05.05. When I do some searches whose hit's number is about 14.000
records the time of search climbs from an average of 2 seconds per search
to 40 to 80 seconds around. I've a virtual machine with 6GB of RAM, with a
virtual Xeon of 2GHz.

Koha is making the OPAC search calling the function getRecords which is in
the lib/C4/Search.pm file. As I've seen this function first makes a call to
the ZOOM::search function and then makes an asynchronous loop for getting
the records (don't do that in ZOOM::search?) and facets, calling the
_ZOOM_event_function. The Zebra search in ZOOM::search is quite fast, and
takes no more than 0.3 seconds to perform the search. It seems that the
delay is in the asynchronous facets in the _ZOOM_event_loop function. Is
not clear to me what exactly the _ZOOM_event_loop is doing, apart from
retrieving the facets, which are not necessary for me.

Can I resolve in some way this problem, getting rid of the _ZOOM_event_loop
or installing other version? As a first step I've enabled plack, which is a
great help in speeding up the application but not in this case.

Thank you very much in advance.