namespace bids

[Erik Mogensen]

I would rather have the inexpensive (O(1)) option of clearing out a
name-space of items by timestamp, as has been suggested several times
earlier.  It is much less complex, and mirrors the existing flush_all.

(1) You would add items (optionally to a name space).

(2) flush_all simply sets "last_flush_all = now()"

(3) flush_namespace would set "last_flush[namespace] = now()"

(4) Normal retrieval would have the following logic:
  if (timestamp_of_cached_item is older than the last_flush_all) remove
object and return null

(5) Retrieval from a name space, same as (4) and then:
  if (timestamp_of_cached_item is older than the last_flush[namespace])
remove object and return null

Internally you would have a table of name spaces and their last flush
(last_flush[])

You have a little problem with cleaning up the last_flush[] table, since
you can't be sure that it's safe to remove *really old* entries, and the
table might grow.
-- 
-mogsie-