Istvan Toth created PHOENIX-6998:
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Summary: Perf regression with server merge query plan for hinted
uncovered indexes
Key: PHOENIX-6998
URL: https://issues.apache.org/jira/browse/PHOENIX-6998
Project: Phoenix
Issue Type: Bug
Components: core
Reporter: Istvan Toth
Server merge indexes can be a huge performance win, especially for limit / TopN
queries that can be resolved on the index table, and which the skip-scan-join
plan does not push down.
However, for a large resultset, and poor index selectivity the new server merge
query plan is still significantly slower than the old skip-scan-join plan.
In one case I had these results:
unindexed query: 52s
hinted skip-scan-join query: 90s
hinted server merge query: 300s
This was a manufactured worst case dataset, but we can still see that new plan
can perform significantly worse than the old one.
As we ultimately read the same cells from both tables, I can only conlcude that
even the new batched server merge performs worse than getting the rows from the
client for large resultsets.
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