[IMPALA-11418] Optimize select contant statement min memory reservation

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 4.0.0, Impala 4.1.0
• Fix Version/s: Impala 4.2.0
• Component/s: Frontend
• Epic Color: ghx-label-2
• Assignee: Xianqing He
• Reporter: Xianqing He
• Created: 06/Jul/22 08:58
• Updated: 27/May/23 13:54
• Resolved: 27/May/23 13:54

Description

If SPOOL_QUERY_RESULTS is true, then the ResourceProfile sets a min reservation in PlanRootSink.

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.
 

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                           |
+--------------------------------------------------------+ 

 

Issue Links

• Blocked: IMPALA-11613 Optimize result spooling for the statement that returns at most one row