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https://issues.apache.org/jira/browse/DRILL-6543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16527117#comment-16527117
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ASF GitHub Bot commented on DRILL-6543:
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Ben-Zvi opened a new pull request #1351: DRILL-6543: Disable Hash Join
fallback, add percent_reserved_allowance_from_direct
URL: https://github.com/apache/drill/pull/1351
(1) Turned the default for Hash Join Fallback to **false**.
(2) Added a new option:
**planner.memory.percent_reserved_allowance_from_direct**
This new option enforces (when a query with buffered operators is run)
reserving part of the Direct Memory for the non-buffered operators. It checks
against the two ways to set the memory (for the buffered operators): Memory per
query per node, or Percent per query.
Also added a test for the enforcement.
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> Options for memory mgmt: Reserve allowance for non-buffered, and Hash-Join
> default to not fallback
> -----------------------------------------------------------------------------------------------------
>
> 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
>
>
> Changes to options related to memory budgeting:
> (1) Change the default for "drill.exec.hashjoin.fallback.enabled" to *false*
> (same as for the similar Hash-Agg option). This would force users to
> calculate and assign sufficient memory for the query, or explicitly choose to
> fallback.
> (2) 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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