[
https://issues.apache.org/jira/browse/IMPALA-7928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16710507#comment-16710507
]
Joe McDonnell commented on IMPALA-7928:
---------------------------------------
One problem I ran into when implementing this is that a simple hash will have
bad behavior if the number of nodes changes. I'm taking a look at consistent
hashes to see if that makes sense. Example:
http://highscalability.com/blog/2018/6/18/how-ably-efficiently-implemented-consistent-hashing.html
> Investigate consistent placement of remote scan ranges
> ------------------------------------------------------
>
> Key: IMPALA-7928
> URL: https://issues.apache.org/jira/browse/IMPALA-7928
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 3.2.0
> Reporter: Joe McDonnell
> Priority: Major
>
> With the file handle cache, it is useful for repeated scans of the same file
> to go to the same node, as that node will already have a file handle cached.
> When scheduling remote ranges, the scheduler introduces randomness that can
> spread reads across all of the nodes. Repeated executions of queries on the
> same set of files will not schedule the remote reads on the same nodes. This
> causes a large amount of duplication across file handle caches on different
> nodes. This reduces the efficiency of the cache significantly.
> It may be useful for the scheduler to introduce some determinism in
> scheduling remote reads to take advantage of the file handle cache. This is a
> variation on the well-known tradeoff between skew and locality.
>
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
