[jira] [Created] (DRILL-6543) Options for memory mgmt: Reserve allowance for non-buffered, and Hash-Join default to not fallback

["Boaz Ben-Zvi (JIRA)" <ji...@apache.org>]

Boaz Ben-Zvi created DRILL-6543:
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             Summary: 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
             Fix For: 1.14.0


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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