[jira] [Commented] (AMQ-7082) KahaDB index, recover free pages in parallel with start

["Gary Tully (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AMQ-7082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16676576#comment-16676576 ] 

Gary Tully commented on AMQ-7082:
---------------------------------

The window is small, however with something like message expiry, and all messages expiring while the broker is down, there can be alot of page file churn immediately after start. In addition if the recovery is very long, the window gets larger.

> KahaDB index, recover free pages in parallel with start
> -------------------------------------------------------
>
>                 Key: AMQ-7082
>                 URL: https://issues.apache.org/jira/browse/AMQ-7082
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: KahaDB
>    Affects Versions: 5.15.0
>            Reporter: Gary Tully
>            Assignee: Gary Tully
>            Priority: Major
>             Fix For: 5.16.0, 5.15.7
>
>
> AMQ-6590 fixes free page loss through recovery. The recover process can be timely, which prevents fast failover, doing recovery on shutdown is preferable, but it is still not ideal b/c it will hold onto the kahadb lock. It also can stall shutdown unexpectedly.
> AMQ-7080 is going to tackle checkpointing the free list. This should help avoid the need for recovery but it may still be necessary. If the perf hit is significant this may need to be optional.
> There will still be the need to walk the index to find the free list.
> It is possible to run with no free list and grow, and we can do that while we recover the free list in parallel, then merge the two at a safe point. This we can do at startup.
> In cases where the disk is the bottleneck this won't help much, but it will help failover and it will help shutdown, with a bit of luck the recovery will complete before we stop.
>  
> Initially I thought this would be too complex, but if we concede some growth while we recover, ie: start with an empty free list, it is should be straight forward to merge with a recovered one.



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)