Yongzhi Chen created HIVE-21075:
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Summary: 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
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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