[jira] [Commented] (DRILL-6543) Option for memory mgmt: Reserve allowance for non-buffered

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-6543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16531800#comment-16531800 ] 

ASF GitHub Bot commented on DRILL-6543:
---------------------------------------

ilooner commented on a change in pull request #1351: DRILL-6543: Disable Hash Join fallback, add percent_reserved_allowance_from_direct
URL: https://github.com/apache/drill/pull/1351#discussion_r199910775
 
 

 ##########
 File path: exec/java-exec/src/test/java/org/apache/drill/exec/util/TestQueryMemoryAlloc.java
 ##########
 @@ -120,6 +123,53 @@ public void testCustomPercent() throws Exception {
     }
   }
 
+  /**
+   *  Test that the percent_reserved_allowance_from_direct limitation works
+   */
+  @Test
+  public void testReservedAllowanceCheck() throws Exception {
+    OperatorFixture.Builder builder = OperatorFixture.builder(dirTestWatcher);
 
 Review comment:
   Thanks for adding a unit test.

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> Option for memory mgmt: Reserve allowance for non-buffered
> ----------------------------------------------------------
>
>                 Key: DRILL-6543
>                 URL: https://issues.apache.org/jira/browse/DRILL-6543
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>    Affects Versions: 1.13.0
>            Reporter: Boaz Ben-Zvi
>            Assignee: Boaz Ben-Zvi
>            Priority: Major
>             Fix For: 1.15.0
>
>
> Introduce a new option to enforce/remind users to reserve some allowance when budgeting their memory:
> The problem: When the "planner.memory.max_query_memory_per_node" (MQMPN) option is set equal (or "nearly equal") to the allocated *Direct Memory*, an OOM is still possible. The reason is that the memory used by the "non-buffered" operators is not taken into account.
> For example, MQMPN == Direct-Memory == 100 MB. Run a query with 5 buffered operators (e.g., 5 instances of a Hash-Join), so each gets "promised" 20 MB. When other non-buffered operators (e.g., a Scanner, or a Sender) also grab some of the Direct Memory, then less than 100 MB is left available. And if all those 5 Hash-Joins are pushing their limits, then one HJ may have only allocated 12MB so far, but on the next 1MB allocation it will hit an OOM (from the JVM, as all the 100MB Direct memory is already used).
> A solution -- a new option to _*reserve*_ some of the Direct Memory for those non-buffered operators (e.g., default %25). This *allowance* may prevent many of the cases like the example above. The new option would return an error (when a query initiates) if the MQMPN is set too high. Note that this option +can not+ address concurrent queries.
> This should also apply to the alternative for the MQMPN - the {{"planner.memory.percent_per_query"}} option (PPQ). The PPQ does not _*reserve*_ such memory (e.g., can set it to %100); only its documentation clearly explains this issue (that doc suggests reserving %50 allowance, as it was written when the Hash-Join was non-buffered; i.e., before spill was implemented).
> The memory given to the buffered operators is the highest calculated between the MQMPN and the PPQ. The new reserve option would verify that this figure allows the allowance.
>  



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