[jira] [Commented] (COLLECTIONS-469) PassiveExpiringMap performance improvemend and refreshing policy

classic Classic list List threaded Threaded
1 message Options
Reply | Threaded
Open this post in threaded view

[jira] [Commented] (COLLECTIONS-469) PassiveExpiringMap performance improvemend and refreshing policy

ASF GitHub Bot (Jira)

    [ https://issues.apache.org/jira/browse/COLLECTIONS-469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13657311#comment-13657311 ]

Thomas Neidhart commented on COLLECTIONS-469:

Although this would only be performant if we do not add a refresh policy. Updating the expiration time for entries in a PriorityQueue for every get() would be O(n + logn) = O(n), not quite ok for map I guess.

> PassiveExpiringMap performance improvemend and refreshing policy
> ----------------------------------------------------------------
>                 Key: COLLECTIONS-469
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-469
>             Project: Commons Collections
>          Issue Type: New Feature
>          Components: Map
>    Affects Versions: 4.0-beta-1
>            Reporter: l0co
>            Priority: Minor
> A copy from COLLECTIONS-467.
> Two remarks about current trunk implementation of PassiveExpiringMap.
> You should additionally keep the value of the next element timeout (the youngest timeout) in object field, so that you don't need to iterate through whole map to find elements for expiration on each call. It improves performance by calculating only simple if for most cases:
> {code}
> public class PassiveExpiringMap {
>   long youngestTimeoutMs = 0; // assert to have next timeout time for youngest element here always, or 0 if map is empty
>   private void removeAllExpired(final long now) {
>     if (youngestTimeoutMs>0 && youngestTimeoutMs<=now) {
>       // do the cleanup
>     }
>   }
> }
> {code}
> The second remark concerns the refreshing policy. As I can see there's no refreshing policy in current implementation, there should be at last two policies: NoRefresh (working as the current) and RefreshOnHit - which updates element expiration time when the element is "hit" (eg. by get()), so that the map always removes the least used resources.

This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira