How do we expect users to understand exec_mem_limit ?

[Yi WU <da...@gmail.com>]

exec_mem_limit is a session variable, which can be set by users. I think we
should define it exactly to make users understood. For example , It is max
memory consumption of a query on a be. If a query consumes memory beyond
exec_mem_limit on a be , it should be failed due to memory allocation.

I am not sure whether the above idea is acceptable.

Now, exec_mem_limit does not work because some memory allocation is not
limited by it due to calling MemPool::allocate. Actually exec_mem_limit
works at fragment instance level, it does not work at query level. However,
FragmentInstance is related to table, users can not expect how many
fragment instances would run on a be, so it is difficult to make users
understood.

Should we let exec_mem_limit limit memory consumption on a query on a be?


The same message is put on discussion.

https://github.com/StarRocks/starrocks/discussions/4069