[jira] [Commented] (DRILL-5370) Drillbit dies for 5 MB SELECT statement

["Paul Rogers (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-5370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15933918#comment-15933918 ] 

Paul Rogers commented on DRILL-5370:
------------------------------------

Output:

{code}
Query Length: 5,243,141
17:49:30.583 [272f877e-f0f4-2e8b-29ef-d4220ab8dac2:foreman] ERROR o.a.drill.exec.work.foreman.Foreman - SYSTEM ERROR: OutOfMemoryError: Java heap space
[Error Id: 6f097f5a-908e-4c54-8d98-6cb47072c9b9 on 172.30.1.69:31010]
org.apache.drill.common.exceptions.UserException: SYSTEM ERROR: OutOfMemoryError: Java heap space
...
Caused by: org.apache.drill.exec.work.foreman.ForemanException: Unexpected exception during fragment initialization: Internal error: Error while applying rule ProjectRemoveRule, args [rel#8891:DrillProjectRel.LOGICAL.ANY([]).[](input=rel#8890:Subset#1.LOGICAL.ANY([]).[],outer1_0…
...
org.apache.drill.common.exceptions.UserRemoteException: SYSTEM ERROR: OutOfMemoryError: Java heap space
{code}

This run did not result in a "catastrophic error, system shut down", but others did.

> Drillbit dies for 5 MB SELECT statement
> ---------------------------------------
>
>                 Key: DRILL-5370
>                 URL: https://issues.apache.org/jira/browse/DRILL-5370
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.10.0
>            Reporter: Paul Rogers
>
> Some community users use Drill with BI tools that generate queries. One such tool generates queries that map Drill data into a "cube" format for a cube-based visualization engine. Such tools tend to create very large, very complex queries.
> In replicating an issue found by this user, I created a simple program that creates deeply-nested queries of the form:
> SELECT a99 AS a98 FROM (SELECT a97 AS a98 FROM(… SELECT a1 FROM myTable)…))
> The test used 200 columns each with names of 500 characters long. (Drill has a hard limit of 1024 characters for a symbol name.)
> The setup was an embedded Drillbit using the new "cluster fixture" test framework. The test ran multiple iterations, each wrapping the prior SELECT in a new one as shown above. The result is a series of queries that grew in size by about 100K each iteration.
> Drill handled SELECT statements up to 5 MB in size, after which the Drillbit ran out of heap memory, suffered a fatal exception and exited.
> One question is why a 5 MB query exhausted multiple GB of heap during query parsing and planning.
> But, more importantly, Drill should have some way to protect itself from such failures. In a production cluster, heap exhaustion will bring down all in-flight queries and require a manual restart of the Drillbit.
> So, Drill should enforce some limit on the amount of heap memory used by a query during the parsing and planning process.
> The community user found a failure at around 1 MB, but they very likely had a query with much more complex structure than the simple nested-SELECT used in my test.



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