[jira] [Commented] (LOG4J2-1282) Make RingBufferLogEvent::mergePropertiesIntoContextMap allocation-free if possible

["Remko Popma (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-1282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15201242#comment-15201242 ] 

Remko Popma commented on LOG4J2-1282:
-------------------------------------

Some initial thoughts: one way to address this issue is to use a different data structure than provided by the java util collections framework.

I noticed that ThreadContextMap is passed downstream as a Map<String,String> but only a small subset of the Map API is used by the downstream client code:
* isEmpty()
* looping over the key-value pairs (currently via entrySet() or keySet()) 
* containsKey(String key)
* get(String key)
* toString()

Both the configuration properties map and the ThreadContext map are likely small (less than 100 entries). We could create a custom gc-free array-based implementation. For the rare cases where client code calls get() or containsKey() without looping over the map contents, a linear scan over the array may perform well enough.


> Make RingBufferLogEvent::mergePropertiesIntoContextMap allocation-free if possible
> ----------------------------------------------------------------------------------
>
>                 Key: LOG4J2-1282
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1282
>             Project: Log4j 2
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 2.5
>            Reporter: Remko Popma
>
> RingBufferLogEvent::mergePropertiesIntoContextMap is called in the background (consumer) thread for each event.
> If configuration properties are specified it allocates the following temporary objects:
> * make mutable copy of the ThreadContext map
> * iterator over configuration properties map
> * for config values containing ${} placeholders, call {{StrSubstitutor.replace}} (which creates multiple temporary objects)
> (If configuration properties are not specified, no temporary objects are allocated.)



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