nickva commented on PR #5625:
URL: https://github.com/apache/couchdb/pull/5625#issuecomment-3212432680
I made two more improvements inspired by some discussions with Mike and Bob:
* Added a priority field to the insert call. So the depth 1 nodes get a
higher initial priority. Priority higher than 1 is basically the initial usage
count, so the entry would survive a few more cleanup intervals.
* When b-trees are updated there is an effect that a root node that was in
use would now become abandoned suddenly. To help evict it faster, since we know
how the b-tree get updated, we can reset its usage count to 0 (not remove it
because some clients may still be reading from the old snapshot, otherwise the
entry stays at least until the next cleanup interval but no more than that)
* If the cache is not very full previously we just leave the entries in
there case they may be reused if there is no pressure on the cache. However
with a longer interval of 1-2 seconds a new set of updates would be prevented
from using the cache for a bit. So the change is that now if we didn't do any
cleanup (we're half empty) then instead of sleeping for 1-2 seconds we checking
the cache size every few hundred milliseconds, so we can react faster to new
entries wanting to use the cache
* To avoid the cache users all calling is_process_alive(Fd), which is
still a process signal send/receive I made the cleaner processes do it
periodically. They gather the processes in a set then delete the dead ones,
that gets the send/recv signal path out of main data path.
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