[LOG4J2-1683] (GC) Avoid allocating temporary objects in MapMessage

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.7
• Fix Version/s: 2.8
• Component/s: API
• Epic Link: GC-free
• Assignee: Remko Popma
• Reporter: Remko Popma
• Created: 08/Nov/16 13:56
• Updated: 20/Nov/16 16:47
• Resolved: 20/Nov/16 16:47

Description

Make MapMessage garbage-free.

While working on LOG4J2-1677, I found that MapFilter itself can avoid allocating temporary objects, but when filtering a MapMessage, the message allocates a java/util/Collections$UnmodifiableMap:

	at java.util.Collections.unmodifiableMap(Collections.java:1318)
	at org.apache.logging.log4j.message.MapMessage.getData(MapMessage.java:102)
	at org.apache.logging.log4j.core.filter.MapFilter.filter(MapFilter.java:70)

Apart from the filtering, logging a MapMessage allocates a StringBuilder and an iterator over the TreeMap:

	at java.lang.StringBuilder.<init>(StringBuilder.java:85)
	at org.apache.logging.log4j.message.MapMessage.asString(MapMessage.java:189)
	at org.apache.logging.log4j.message.MapMessage.asString(MapMessage.java:172)
	at org.apache.logging.log4j.message.MapMessage.getFormattedMessage(MapMessage.java:229)
	at org.apache.logging.log4j.core.async.RingBufferLogEvent.setMessage(RingBufferLogEvent.java:127)

Issue Links

• depends upon: LOG4J2-1681 Introduce interfaces IndexedStringMap and IndexedReadOnlyStringMap
• is depended upon by: LOG4J2-1684 (GC) Avoid allocating temporary objects in StructuredDataMessage
• is depended upon by: LOG4J2-1677 (GC) Avoid allocating temporary objects in MapFilter