[horde] temp files in horde

[cheese at nosuchhost.net]

dear all,

hope you are being healthy even during corona-time.

i have a question concerning $conf['tmpdir'] from conf.php

we have several horde-instances behind a loadbalancer and those hordes 
share a single tmpdir. 
this was because if we take down one of our horde-machine for 
maintenance we would like our users to be able to work without interruption.

now we see alot of files in that shared folder:

* we have a lot of img* files, some of them with size 0
* Horde* files, some of them empty, some with image-data, some with 
contents of adressbooks
* horde_dns.cache - we once had troubles as that file got currupted and 
all apaches crashed because of that.
* horde_form* - most of them empty
* impatt* - seem to be attachments
* php* - images and other data
* .horde/imp/compose/uuid files - some seem to be complete mails, some 
just images, zip-files

are there any implications in sharing those folder between all instances 
of our hordes? maybe horde1 and horde2 try to use the same file?

how often should we delete files from that folder. we had lots of old 
files there, some of them several weeks or even months.

any best-practise from other installations?

thanks for all input
yours
josef