Its depend on your server hardware model and type, Its all depend on how much memory you have on server how many users are running searches etc.Lets you have 8 core 24GRam right for 40 users one search head is enough.
max_hist_searches = max_searches_per_cpu x number_of_cpus + base_max_searches
To fix the problem more generally, you can tweak some configuration nobs in limits.conf as follows:
a) max_searches_per_cpu
While increasing this could fix the dashboard issue where searches are fairly cheap to run, this could lead to performance degradation if you've scheduled a large number of expensive searches.
b) dispatch_quota_retry
This is the number of retries the back end will attempt before throwing the quota/limit error. The back end here does an exponential back-off starting with 100ms and doubling that every time it retries.
c) dispatch_quota_sleep_ms
The initial sleep time for retries. Instead of increasing max_searches_per_cpu you can set the dispatch_quota_retry to 10 which will instruct the back-end to retry dispatching a particular search for about 100 seconds before throwing the quota/limit error.
