[ https://issues.jboss.org/browse/JGRP-1990?page=com.atlassian.jira.plugin.... ] Bela Ban commented on JGRP-1990: -------------------------------- The memory savings are nice: {noformat} org.jgroups.util.Headers object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 short[] Headers.ids N/A 16 4 Header[] Headers.hdrs N/A 20 4 (loss due to the next object alignment) Instance size: 24 bytes (estimated, the sample instance is not available) Space losses: 0 bytes internal + 4 bytes external = 4 bytes total {noformat} A message had a ref to a {{Headers}} instance, which had refs to an {{id}} (carrying the prot-ids) and a {{headers}} array (carrying the actual headers). A {{Headers}} instances takes roughly 24 bytes of memory as shown above. Half of that is the cost of the _object header_ (12 bytes)! The new message has a ref to a {{Header[]}} array, in which all headers are stored. The {{Header}} abstract superclass now also carries a short which adds 2 bytes to each header. The advantages of this new approach, which stores headers directly in an array of {{Message}} are: * Less memory need: the overall cost of maintaining headers (without the cost of the actual headers) is now ~ 24 bytes - 2 bytes = *22 bytes lower* (per message) ! * If the headers array needs to be grown, we only have to grow 1 rather than 2 arrays -- This message was sent by Atlassian JIRA (v6.4.11#64026)