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https://issues.apache.org/jira/browse/HIVE-9768?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hari Sekhon updated HIVE-9768:
------------------------------
Description:
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 original trio of Impala SMEs at Cloudera in early 2013)
Regards,
Hari Sekhon
ex-Cloudera
http://www.linkedin.com/in/harisekhon
was:
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
> 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: llap
> 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 original trio of Impala SMEs at Cloudera in early 2013)
> Regards,
> Hari Sekhon
> ex-Cloudera
> http://www.linkedin.com/in/harisekhon
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