nickva commented on PR #5625:
URL: https://github.com/apache/couchdb/pull/5625#issuecomment-3202005847
Update the PR with these changes:
* As a safety precaution add a `is_process_alive(Fd)` check after we fetch
the item from the cache. Behind the scenes that still sends a signal to the
process so it will add some overhead but it seems safer. If the process is
already dead, the cache returns `undefined` as if the item is missing and then
cleans any other entries associated with that `Fd`. The caller will then try to
fetch the term from `couch_file` and crash like it would without the cache.
* Parameterized the percentage of max size below which entries are left
around in the cache. That is if the cache is mostly empty then some entries
with 0 bump_counts are left around in there in case they may be needed again.
The tradeoff here is that if a bunch of new work come suddenly it may find the
cache full until the next cleanup cycles removes all the 0 entries. This will
let us test some of the scenarios mentioned like what happens if most entries
are already in the cache.
* Added a 3rd `[couchdb, bt_engine_cache, full]` metric which is bumped
when tried to insert into the cache but it was full.
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