Remove unneeded weak reference from prefix logger #22460
We have a custom logger implementation known as a prefix logger that is used to write every message by the logger with a given prefix. This is useful for node-level, index-level, and shard-level messages where we want to log the node name, index name, and shard ID, respectively, if possible. The mechanism that we employ is that of a marker. Log4j has a built-in facility for managing these markers, but its effectively a memory leak because these markers are held in a map and can never be released. This is problematic for us since indices and shards do not necessarily have infinite life spans and so on a node where there are many indices being creted and destroyed, this infinite lifespan can be a problem indeed. To solve this, we use our own cache of markers. This is necessary to prevent too many instances of the marker for the same prefix from being created (just think of all the shard-level components that exist in the system), and to workaround the effective leak in Log4j. These markers are stored as weak references in a weak hash map. It is these weak references that are unneeded. When a key is removed from a weak hash map, the corresponding entry is placed on a reference queue that is eventually cleared. This commit simplifies prefix logger by removing this unnecessary weak reference wrapper.