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https://issues.apache.org/jira/browse/DRILL-5972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16270608#comment-16270608
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ASF GitHub Bot commented on DRILL-5972:
---------------------------------------
Github user asfgit closed the pull request at:
https://github.com/apache/drill/pull/1038
> Slow performance for query on INFORMATION_SCHEMA.TABLE
> ------------------------------------------------------
>
> Key: DRILL-5972
> URL: https://issues.apache.org/jira/browse/DRILL-5972
> Project: Apache Drill
> Issue Type: Bug
> Components: Storage - Information Schema
> Affects Versions: 1.11.0
> Reporter: Padma Penumarthy
> Assignee: Padma Penumarthy
> Labels: ready-to-commit
> Fix For: 1.12.0
>
>
> A query like the following on INFORMATION_SCHEMA takes a long time to
> execute.
> select TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME, TABLE_TYPE from
> INFORMATION_SCHEMA.`TABLES` WHERE TABLE_NAME LIKE '%' AND ( TABLE_SCHEMA =
> 'hive.default' ) ORDER BY TABLE_TYPE, TABLE_CATALOG, TABLE_SCHEMA,
> TABLE_NAME;
> Reason being we fetch table information for all schemas instead of just
> 'hive.default' schema.
> If we change the predicate like this, it executes very fast.
> select TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME, TABLE_TYPE from
> INFORMATION_SCHEMA.`TABLES` WHERE ( TABLE_SCHEMA = 'hive.default' ) AND
> TABLE_NAME LIKE '%' ORDER BY TABLE_TYPE, TABLE_CATALOG, TABLE_SCHEMA,
> TABLE_NAME;
> The difference is in the order in which we evaluate the expressions in the
> predicate.
> In the first case, we first evaluate TABLE_NAME LIKE '%' and decide that it
> is inconclusive (since we do not know the schema). So, we go get all tables
> for all the schemas.
> In the second case, we first evaluate TABLE_SCHEMA = 'hive.default' and
> decide that we need to fetch only tables for that schema.
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