Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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v3.0.0-alpha2, v2.6.4
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None
Description
Hi Kylin team,
I found an issue while server side PreparedStatement enabled. The second time query and after's result will be different from the first when query TopN, and the result is not right.
Part of Cube info:
Dimensions
TRANS_ID
PART_DT
SELLER_ID
BUYER_ID
Measures:
SUM(PRICE)
MAX(PRICE)
TOPN(PRICE) Group By:KYLIN_SALES.SELLER_ID,KYLIN_SALES.BUYER_ID
SQL:
{"sql":"select seller_id, buyer_id, sum(PRICE) from glaucus.kylin_sales where PART_DT >= ? and PART_DT <= ? group by seller_id, buyer_id order by sum(PRICE) desc limit 20","project":"DDTFORTEST_Analytics", "params":[{"className": "java.lang.String","value": "2012-01-01"},{"className": "java.lang.String","value": "2012-01-10"}]}
The First query result:
The Second and after:
-----------------------------------------------
Root Cause
Cached preparedContext is changed when doing preparedStatement.executeQuery, and losing groupByColumns. So the first execution result is correct, the second and the after will be incorrect.
Real Root Cause
The first time we entered PreparedStatement logic, we'll try to borrow preparedContext from cache pool, of course there isn't any, but the cache pool will execute create method to create a new preparedContext, and then loaned it to us.
I didn't figure out how adjustSqlDigest works before, and try to remove code
sqlDigest.groupbyColumns.removeAll(topnLiteralCol)
but it's not right. Top-N isn't like some other measures, the dimensions aren't as part of row key, they stored in measures in design, so it's why the adjustSqlDigest matters, especially those codes.
sqlDigest.groupbyColumns.removeAll(topnLiteralCol); sqlDigest.metricColumns.addAll(topnLiteralCol);
The root cause for this issue is because the create sql digest is execute again after we store it in cache, so the digest changed.
# This is from the first time fact table GLAUCUS.KYLIN_SALES,group by [],filter on [GLAUCUS.KYLIN_SALES.PART_DT],with aggregates[FunctionDesc [expression=TOP_N, parameter=GLAUCUS.KYLIN_SALES.PRICE,GLAUCUS.KYLIN_SALES.SELLER_ID,GLAUCUS.KYLIN_SALES.BUYER_ID, returnType=topn(5000,8)]]. # This is the second one fact table GLAUCUS.KYLIN_SALES,group by [],filter on [GLAUCUS.KYLIN_SALES.PART_DT],with aggregates[FunctionDesc [expression=SUM, parameter=GLAUCUS.KYLIN_SALES.PRICE, returnType=decimal(19,4)]].
So the second time and after we execute the same query or same pattern, the expression will be changed to SUM instead of TOPN, that's why the strange result show up.
