Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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None
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None
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None
Description
Queries against INFORMATION_SCHEMA.TABLES and INFORMATION_SCHEMA.VIEWS slow down as the number of views increases.
BI tools like Tableau issue a query like the following at connection time:
select TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME, TABLE_TYPE from INFORMATION_SCHEMA.`TABLES` WHERE TABLE_CATALOG LIKE 'DRILL' ESCAPE '\' AND TABLE_SCHEMA <> 'sys' AND TABLE_SCHEMA <> 'INFORMATION_SCHEMA'ORDER BY TABLE_TYPE, TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME
The time to query the information schema tables degrades as the number of views increases. On a test system:
| Views | Time(secs) |
|---|---|
| 500 | 6 |
| 1000 | 19 |
| 1500 | 33 |
This can result in a single connection taking more than a minute to establish.
The problem occurs because we read the view file for every view and this appears to take most of the time.
Querying information_schema.tables does not, in fact, need to open the view file at all, it merely needs to get a listing of the view files. Eliminating the view file read will speed up the query tremendously.
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