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Posted to issues@hive.apache.org by "Alan Gates (JIRA)" <ji...@apache.org> on 2015/02/24 18:19:04 UTC
[jira] [Commented] (HIVE-9768) Hive LLAP Metadata pre-load for low
latency, + cluster-wide metadata refresh/invalidate command
[ https://issues.apache.org/jira/browse/HIVE-9768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14335109#comment-14335109 ]
Alan Gates commented on HIVE-9768:
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-1. We don't want to be caching metadata and forcing users to invalidate it. We can figure out how to make things fast enough without this. If we cannot, then we'll figure out how to do the invalidation automatically. But forcing users to do it is way too error prone.
> Hive LLAP Metadata pre-load for low latency, + cluster-wide metadata refresh/invalidate command
> -----------------------------------------------------------------------------------------------
>
> Key: HIVE-9768
> URL: https://issues.apache.org/jira/browse/HIVE-9768
> Project: Hive
> Issue Type: New Feature
> Components: HCatalog, Metastore, Query Planning, Query Processor
> Affects Versions: 0.14.0, llap, 1.0.0
> Environment: HDP 2.2
> Reporter: Hari Sekhon
>
> Feature request for Hive LLAP to preload table metadata across all running nodes to reduce query latency (this is what Impala does).
> The design decision behind this in Impala was to avoid the latency overhead of fetching the metadata at query time, since that's an extra database query (or possibly HBase query in future HIVE-9452) that must first be completely fullfilled before the Hive LLAP query even starts to run, which would slow down the response to the user if not pre-loaded. Also, any temporary outage of the metadata layer would affect the speed LLAP layer so pre-loading and caching the metadata adds resilience against this.
> This pre-loaded metadata also requires a cluster-wide "refresh metadata" operation, something Impala added later, and now calls "INVALIDATE METADATA" in it's SQL dialect. I propose using a more intuitive "REFRESH METADATA" Hive command instead.
> (Fyi I was in the first trio of Impala SMEs at Cloudera in early 2013)
> Regards,
> Hari Sekhon
> ex-Cloudera
> http://www.linkedin.com/in/harisekhon
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