[jboss-jira] [JBoss JIRA] Commented: (JGRP-806) Message: investigate making the overhead for headers smaller

[Michal Frajt (JIRA)]

    [ https://jira.jboss.org/jira/browse/JGRP-806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12423114#action_12423114 ] 

Michal Frajt commented on JGRP-806:
-----------------------------------

I've reviewed your changes.  Here are my comments:

- resize() method
The very common practice in all Collection classes is to double the current size of an underlying structure. The static increment can be fine as we do not expect more headers to be added anyway.

- synchronized resize()
Either the class is synchronized or non-synchronized. One synchronized method will not protected malfunctionality if the object is used from multiple threads without monitor (adds overwriting same index etc). I do prefer to remove the synchronized to strongly indicate that the whole Message object is non synchronized data structure.

- garbage less iteration not possible
The only way to iterate over the headers seems to be the method returning constructed HashMap.
Running a debuging (processing /displaying of headers) would than return the garbage cost to the previous solution. You should take care that non of the protocol stacks or other parts of the code are using the getHeaders method frequently. Solution might be to add methods String getHeaderName(int index) and Header getHeader(int index) for the fast iterator using the index (see RandomAccess of the ArrayList). The method to return the max index (getHeaderNum() is already available). The method with HashMap can/must stay for compatility. 

I might come with some more optimalizations of other parts as we are going to continue with the JGroups testing/integration in next weeks. I just recall that there was some code like new HashSet(1) for one element. You should use the Colllections.singleton metod for size 1, Collection.emptySet for empty sets and have your own smart set implementation (like new Headers) for sets < ~10. It can give same benefits as the current changes done on the headers. 

Michal


> Message: investigate making the overhead for headers smaller
> ------------------------------------------------------------
>
>                 Key: JGRP-806
>                 URL: https://jira.jboss.org/jira/browse/JGRP-806
>             Project: JGroups
>          Issue Type: Task
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 2.6.4, 2.7
>
>
> Related to https://jira.jboss.org/jira/browse/JGRP-805.
> See whether we can make the overhead for ConcurrentHashmap in Message smaller. Potentially reduce the number of buckets for each CCHM (default: 16, IIRC). Or replace CCHMs altogether ?

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