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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6157) Fetching column stats slower than the 101 during rush hour
Date Mon, 20 Jan 2014 17:22:21 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13876591#comment-13876591
] 

Sergey Shelukhin commented on HIVE-6157:
----------------------------------------

Sorry, was not aware of that JIRA. Among other things, this patch adds bulk APIs. They do
not support multiple tables as of now, though. Stats are currently fetched on the level of
one column (stat optimizer) or one table (table scan stuff), so making use of multi-table
API would require more extensive changes on the client (optimizer) side.

> Fetching column stats slower than the 101 during rush hour
> ----------------------------------------------------------
>
>                 Key: HIVE-6157
>                 URL: https://issues.apache.org/jira/browse/HIVE-6157
>             Project: Hive
>          Issue Type: Bug
>    Affects Versions: 0.13.0
>            Reporter: Gunther Hagleitner
>            Assignee: Sergey Shelukhin
>         Attachments: HIVE-6157.prelim.patch
>
>
> "hive.stats.fetch.column.stats" controls whether the column stats for a table are fetched
during explain (in Tez: during query planning). On my setup (1 table 4000 partitions, 24 columns)
the time spent in semantic analyze goes from ~1 second to ~66 seconds when turning the flag
on. 65 seconds spent fetching column stats...
> The reason is probably that the APIs force you to make separate metastore calls for each
column in each partition. That's probably the first thing that has to change. The question
is if in addition to that we need to cache this in the client or store the stats as a single
blob in the database to further cut down on the time. However, the way it stands right now
column stats seem unusable.



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