Too many open files SRX

[gwbischof]

We are getting a "too many open files" error with databroker-tiled when loading data at SRX. This can be worked around by using databroker-intake and running

db._catalog._entries.cache_clear()

[tacaswell]

In both this case and #702 the core issue is an intake level cache is too big. Is there anyway we can make that smaller by default?

[gwbischof]

This issue also affects databroker without tiled. So we may need a fix for both databroker versions