alex created PHOENIX-846:
----------------------------
Summary: Select DISTINCT with LIMIT does full scans
Key: PHOENIX-846
URL: https://issues.apache.org/jira/browse/PHOENIX-846
Project: Phoenix
Issue Type: Bug
Affects Versions: 3.0.0, 4.0.0
Reporter: alex
Priority: Critical
When running SELECT DISTINCT with LIMIT it does full scan on the server side
(no pageFilter/limit used on server side),
this severely affects performance (query returns in 20sec vs 300ms without
DISTINCT)
: jdbc:phoenix:localhost> explain select DISTINCT ROWKEY from TEST_1M LIMIT 100;
+------------+
| PLAN |
+------------+
| CLIENT PARALLEL 30-WAY FULL SCAN OVER TEST_1M |
| SERVER FILTER BY FIRST KEY ONLY |
| SERVER AGGREGATE INTO ORDERED DISTINCT ROWS BY [ROWKEY] |
| CLIENT MERGE SORT |
| CLIENT 100 ROW LIMIT |
+------------+
-------------------------------------------------
for comparison SELECT without DISTINCT uses a limit PageFilter=100 on server
side and doesn't do full scan (query returns in 300ms)
explain select ROWKEY from TEST_1M LIMIT 100;
+------------+
| PLAN |
+------------+
| CLIENT PARALLEL 30-WAY FULL SCAN OVER TEST_1M |
| SERVER FILTER BY FIRST KEY ONLY AND PageFilter 100 |
| CLIENT MERGE SORT |
| CLIENT 100 ROW LIMIT |
+------------+
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