Xianqing He created IMPALA-11418:
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Summary: Optimize select contant statement min memory reservation
Key: IMPALA-11418
URL: https://issues.apache.org/jira/browse/IMPALA-11418
Project: IMPALA
Issue Type: Improvement
Components: Frontend
Affects Versions: Impala 4.1.0
Reporter: Xianqing He
Assignee: Xianqing He
Fix For: Impala 4.2.0
If SPOOL_QUERY_RESULTS is true, then the ResourceProfile sets a min
reservation.
For the statement 'select 1', the min reservation is 4MB. It's no problem if
the cluster has enough mem available within its process limit to execute the
query. But if the host mem not available it will throw 'Failed to get minimum
memory reservation'.
Some connection pools use 'select 1' to check whether the connection is
available. The check will fail if memory is oversubscribed.
For this case we can set the min reservation to 0 to reduce failure when the
memory is oversubscribed.
{code:java}
Query: explain select 1
+--------------------------------------------------------+
| Explain String |
+--------------------------------------------------------+
| Max Per-Host Resource Reservation: Memory=4MB Threads=1 |
| Per-Host Resource Estimates: Memory=10MB |
| Codegen disabled by planner |
| |
| PLAN-ROOT SINK |
| | |
| 00:UNION |
| constant-operands=1 |
| row-size=1B cardinality=1 |
+--------------------------------------------------------+ {code}
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