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https://issues.apache.org/jira/browse/HIVE-21075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16731601#comment-16731601
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Peter Vary commented on HIVE-21075:
-----------------------------------
[~karthik.manamcheri], [~ychena] we had similar thoughts with [~szita] and
found out that different queries provide optimal performance for different
supported backend DBs. Please keep this in mind when testing solutions.
Seemingly small changes in CD related queries can multiply when having big
number of existing partitions.
> Metastore: Drop partition performance downgrade with Postgres DB
> ----------------------------------------------------------------
>
> Key: HIVE-21075
> URL: https://issues.apache.org/jira/browse/HIVE-21075
> Project: Hive
> Issue Type: Bug
> Components: Metastore
> Affects Versions: 3.0.0
> Reporter: Yongzhi Chen
> Priority: Major
>
> In order to workaround oracle not supporting limit statement caused
> performance issue, HIVE-9447 makes all the backend DB run select count(1)
> from SDS where SDS.CD_ID=? to check if the specific CD_ID is referenced in
> SDS table before drop a partition. This select count(1) statement does not
> scale well in Postgres, and there is no index for CD_ID column in SDS table.
> For a SDS table with with 1.5 million rows, select count(1) has average 700ms
> without index, while in 10-20ms with index. But the statement before
> HIVE-9447( SELECT * FROM "SDS" "A0" WHERE "A0"."CD_ID" = $1 limit 1) uses
> less than 10ms .
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