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https://issues.apache.org/jira/browse/HIVE-17684?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16556103#comment-16556103
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Misha Dmitriev commented on HIVE-17684:
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I agree that any fixing/reconfiguring of tests should be done in a separate
patch. I would also agree that tests that exercise GcTimeMonitor should not be
used as an indirect way to verify that the test infrastructure is working well
- it would be too confusing. But perhaps it's worth creating a Jira about
better monitoring the Hive test JVMs or some such.
So, for now we should either not run this code in tests, or run it with a
rather high GC time threshold. But how does any code in Hive find out whether
it's running in tests or in production? So far I've found
{{HiveConf.getBoolVar(conf, HiveConf.ConfVars.HIVE_IN_TESTS). But from looking
into the source code I am not sure it always works as intended, and access to a
Configuration instance needed by the call above seems to be tricky in
Operator.java - this thing is passed in quite late, in the initialize() method.
Probably I can work around this, but I would like to confirm first that this
HIVE_IN_TESTS is the right thing to use here.}}
> HoS memory issues with MapJoinMemoryExhaustionHandler
> -----------------------------------------------------
>
> Key: HIVE-17684
> URL: https://issues.apache.org/jira/browse/HIVE-17684
> Project: Hive
> Issue Type: Bug
> Components: Spark
> Reporter: Sahil Takiar
> Assignee: Misha Dmitriev
> Priority: Major
> Attachments: HIVE-17684.01.patch, HIVE-17684.02.patch,
> HIVE-17684.03.patch
>
>
> We have seen a number of memory issues due the {{HashSinkOperator}} use of
> the {{MapJoinMemoryExhaustionHandler}}. This handler is meant to detect
> scenarios where the small table is taking too much space in memory, in which
> case a {{MapJoinMemoryExhaustionError}} is thrown.
> The configs to control this logic are:
> {{hive.mapjoin.localtask.max.memory.usage}} (default 0.90)
> {{hive.mapjoin.followby.gby.localtask.max.memory.usage}} (default 0.55)
> The handler works by using the {{MemoryMXBean}} and uses the following logic
> to estimate how much memory the {{HashMap}} is consuming:
> {{MemoryMXBean#getHeapMemoryUsage().getUsed() /
> MemoryMXBean#getHeapMemoryUsage().getMax()}}
> The issue is that {{MemoryMXBean#getHeapMemoryUsage().getUsed()}} can be
> inaccurate. The value returned by this method returns all reachable and
> unreachable memory on the heap, so there may be a bunch of garbage data, and
> the JVM just hasn't taken the time to reclaim it all. This can lead to
> intermittent failures of this check even though a simple GC would have
> reclaimed enough space for the process to continue working.
> We should re-think the usage of {{MapJoinMemoryExhaustionHandler}} for HoS.
> In Hive-on-MR this probably made sense to use because every Hive task was run
> in a dedicated container, so a Hive Task could assume it created most of the
> data on the heap. However, in Hive-on-Spark there can be multiple Hive Tasks
> running in a single executor, each doing different things.
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