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https://issues.apache.org/jira/browse/HIVE-19605?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16484623#comment-16484623
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Todd Lipcon commented on HIVE-19605:
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It seems like this table can also be called from a get_table call. Oddly, the
query being generated is:
SELECT 'org.apache.hadoop.hive.metastore.model.MTableColumnStatistics' AS
NUCLEUS_TYPE,`A0`.`AVG_COL_LEN`,`A0`.`COLUMN_NAME`,`A0`.`COLUMN_TYPE`,`A0`.`DB_NAME`,`A0`.`BIG_DECIMAL_HIGH_VALUE`,`A0`.`BIG_DECIMAL_LOW_VALUE`,`A0`.`DOUBLE_HIGH_VALUE`,`A0`.`DOUBLE_LOW_VALUE`,`A0`.`LAST_ANALYZED`,`A0`.`LONG_HIGH_VALUE`,`A0`.`LONG_LOW_VALUE`,`A0`.`MAX_COL_LEN`,`A0`.`NUM_DISTINCTS`,`A0`.`NUM_FALSES`,`A0`.`NUM_NULLS`,`A0`.`NUM_TRUES`,`A0`.`TABLE_NAME`,`A0`.`CS_ID`
FROM `TAB_COL_STATS` `A0` WHERE `A0`.`DB_NAME` = '';
(note the empty db_name).
Given the lack of index, this takes 450ms on the HMS instance I am testing (if
the mysql query cache is disabled)
> TAB_COL_STATS table has no index on db/table name
> -------------------------------------------------
>
> Key: HIVE-19605
> URL: https://issues.apache.org/jira/browse/HIVE-19605
> Project: Hive
> Issue Type: Bug
> Components: Metastore
> Reporter: Todd Lipcon
> Priority: Major
>
> The TAB_COL_STATS table is missing an index on (CAT_NAME, DB_NAME,
> TABLE_NAME). The getTableColumnStatistics call queries based on this tuple.
> This makes those queries take a significant amount of time in large
> metastores since they do a full table scan.
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