[
https://issues.apache.org/jira/browse/ACCUMULO-4353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15347238#comment-15347238
]
Josh Elser commented on ACCUMULO-4353:
--------------------------------------
bq. If multiple tablet servers die in quick succession, such as from a rolling
restart of the Accumulo cluster or a network partition, this behavior can cause
a storm of reassignment and rebalancing, placing significant load on the master.
In the case of a rolling-restart, isn't that more of an operational issue to
solve (give Accumulo time to process the reassignments before restarting more
nodes)?
Can you expand a bit more on the specifics behind a network partition that
you're trying to solve with this? Say, you lose a node? A rack? Half of your
racks? Are we talking about a 5second interruption/delay? 30s? Minutes?
bq. To avert such load, Accumulo should be capable of maintaining a steady
tablet assignment state in the face of transient tablet server loss. Instead of
reassigning tablets as quickly as possible, Accumulo should be await the return
of a temporarily downed tablet server (for some configurable duration) before
assigning its tablets to other tablet servers.
I'm a little worried about this as a configuration knob -- I feel like it kind
of goes against the highly-available distributed database which we expect
Accumulo to be. When we don't reassign tablets fast, that is a direct lack of
availability for clients to read data.
bq. placing significant load on the master
Can you expand on this some more? Given that assignment is arguably the most
important thing for the Master to do, why are we concerned about letting the
master do that as fast as it can (for the aforementioned reason)? Do we need to
come up with a more efficient way for the master to handle the reassignment of
many tablets? For example, I know that HBase has special logic to batch
assignments together in one RPC call to regionservers in order to bring things
online more quickly (I'm not sure if we have logic like that -- instead we just
spam requests to a tabletserver to load a tablet until it does so).
While seeing a pull request accompanying the issue reported, It seems a bit
premature to me to see code without some discussion on what the problems are
and how best to solve them.
> Stabilize tablet assignment during transient failure
> ----------------------------------------------------
>
> Key: ACCUMULO-4353
> URL: https://issues.apache.org/jira/browse/ACCUMULO-4353
> Project: Accumulo
> Issue Type: Improvement
> Reporter: Shawn Walker
> Assignee: Shawn Walker
> Priority: Minor
> Time Spent: 10m
> Remaining Estimate: 0h
>
> When a tablet server dies, Accumulo attempts to reassign the tablets it was
> hosting as quickly as possible to maintain availability. If multiple tablet
> servers die in quick succession, such as from a rolling restart of the
> Accumulo cluster or a network partition, this behavior can cause a storm of
> reassignment and rebalancing, placing significant load on the master.
> To avert such load, Accumulo should be capable of maintaining a steady tablet
> assignment state in the face of transient tablet server loss. Instead of
> reassigning tablets as quickly as possible, Accumulo should be await the
> return of a temporarily downed tablet server (for some configurable duration)
> before assigning its tablets to other tablet servers.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
