[jira] [Created] (SOLR-17597) CaffeineCache ramBytes incorrect accounting on `put()`

["Michael Gibney (Jira)" <ji...@apache.org>]

Michael Gibney created SOLR-17597:
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             Summary: CaffeineCache ramBytes incorrect accounting on `put()`
                 Key: SOLR-17597
                 URL: https://issues.apache.org/jira/browse/SOLR-17597
             Project: Solr
          Issue Type: Bug
    Affects Versions: 9.7, main (10.0)
            Reporter: Michael Gibney
            Assignee: Michael Gibney


In most cases, usage of {{CaffeineCache.put()}} results in incorrect ramBytes accounting. Replaced values (and keys) decrement {{ramBytes}} via {{onRemoval()}}, so replaced values currently end up double-decrementing for the replaced value in [recordRamBytes()|https://github.com/apache/solr/blob/a4229e76771da0125b38204db01ea0934e09c4f4/solr/core/src/java/org/apache/solr/search/CaffeineCache.java#L297-L301].

After a sufficient number of replacements via {{put()}}, {{ramBytes}} becomes permanently negative, and is thus useless.

The problem was masked in existing tests due to the behavior of the Caffeine library in the case of reference equality between the old (replaced) value and the new (replacement) value for the same ({{.equals()}}) key -- [the case exercised in existing tests|https://github.com/apache/solr/blob/a4229e76771da0125b38204db01ea0934e09c4f4/solr/core/src/test/org/apache/solr/search/TestCaffeineCache.java#L342-L345] -- in which case {{onRemoval()}} is _not_ invoked (so there is no double decrement).

The problem is also masked in normal usage, since existing/default cache implementations and invocation all currently use {{computeIfAbsent()}} instead of {{put()}}.



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