Hi folks,

We're about half way complete in migrating our YARN batch processing 
applications from Flink 1.9 to 1.11, and are currently tackling the memory 
configuration migrations.

Our test application's sink failed with the following exception while writing 
to HDFS:

Caused by: java.lang.OutOfMemoryError: Direct buffer memory. The direct 
out-of-memory error has occurred. This can mean two things: either job(s) 
require(s) a larger size of JVM direct memory or there is a direct memory leak. 
The direct memory can be allocated by user code or some of its dependencies. In 
this case 'taskmanager.memory.task.off-heap.size' configuration option should 
be increased. Flink framework and its dependencies also consume the direct 
memory, mostly for network communication. The most of network memory is managed 
by Flink and should not result in out-of-memory error. In certain special 
cases, in particular for jobs with high parallelism, the framework may require 
more direct memory which is not managed by Flink. In this case 
'taskmanager.memory.framework.off-heap.size' configuration option should be 
increased. If the error persists then there is probably a direct memory leak in 
user code or some of its dependencies which has to be investigated and fixed. 
The task executor has to be shutdown...

We submit our applications through a Flink YARN session with -ytm, -yjm etc. We 
don't have any memory configurations options set aside from 
'taskmanager.network.bounded-blocking-subpartition-type: file' which I see is 
now deprecated and replaced with a new option defaulted to 'file' (which works 
for us!) SO nearly everything else is as default.

We haven't made any configuration changes yet thus far as we're still combing 
through the migration instructions, but I did have some questions around what I 
observed.

1.     I observed that an application ran with "-ytm 12288" on 1.9 receives 
8.47GB JVM Heap space and 5.95 Flink Managed Memory space  (as reported by the 
ApplicationMaster), where on 1.11 it receives 5.79 JVM Heap space and 4.30 
Flink Managed Memory space.  Why does this ~30% memory reduction happen?

2.     Piggybacking off point 1, on 1..9 we were not explicitly setting 
off-heap memory parameters. How would you suggest discerning what properties we 
should have a look at?

Best,
Andreas

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