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https://issues.apache.org/jira/browse/HIVE-3917?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565667#comment-13565667
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Gang Tim Liu commented on HIVE-3917:
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[~shreepadma] sorry to not fully understand your initial question.
[~ashutoshc] thank you very much for explaining it in more details and carrying
the discussion. great! thanks.
Yes, partial scan is a great choice. Actually, we have thought about it. With
https://cwiki.apache.org/Hive/rcfilecat.html, we can even achieve it for RCFile.
Yes, it will be faster than full scan but still slower than noscan. Consider a
big data warehouse, partial scan is still magnitude slower than noscan. With
potential speedup from simple MR, it will be sill slower than noscan.
Saying that, we can view all 3 as great choices for different use cases:
noscan, partial scan and full scan (which is default).
I will create a follow up for partial scan.
> Support fast operation for analyze command
> ------------------------------------------
>
> Key: HIVE-3917
> URL: https://issues.apache.org/jira/browse/HIVE-3917
> Project: Hive
> Issue Type: Improvement
> Components: Statistics
> Affects Versions: 0.11.0
> Reporter: Gang Tim Liu
> Assignee: Gang Tim Liu
> Attachments: HIVE-3917.patch.1
>
>
> hive supports analyze command to gather statistics from existing
> tables/partition
> https://cwiki.apache.org/confluence/display/Hive/StatsDev#StatsDev-ExistingTables
> It collects:
> 1. Number of Rows
> 2. Number of files
> 3. Size in Bytes
> If table/partition is big, the operation would take time since it will open
> all files and scan all data.
> It would be nice to support fast operation to gather statistics which doesn't
> require to open all files:
> 1. Number of files
> 2. Size in Bytes
> Potential syntax is
> ANALYZE TABLE tablename [PARTITION(partcol1[=val1], partcol2[=val2], ...)]
> COMPUTE STATISTICS [noscan];
> In the future, all statistics without scan can be retrieved via this optional
> parameter.
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