Re: [report] memory leaks in COPY FROM on partitioned table

On 2018-Jul-24, Amit Langote wrote:

> Your patch takes care of allocation happening inside
> get_partition_for_tuple, but as you mention there might be others in its
> caller ExecFindPartition.  So, I think we should switch to the per-tuple
> context in ExecFindPartition.

Right, makes sense.  Pushed that way.  I also moved the
ExecFetchSlotTuple call to happen after the memcxt change, because it
seemed to me that it may be possible for tuple_expand to allocate memory
(if not, it's not obvious).  I also reworded some comments -- hope not
to have broken anything too bad there.  I also renamed variable
"parent", which confused the heck out of me.

I had conflicts when applying this in master after developing it in
pg11, because of some new development there (and my variable rename).  I
really hope we don't open the pg13 tree as early as we opened the pg12
one ...

> When I tried to do that, I discovered that we have to be careful about
> releasing some of the memory that's allocated in ExecFindPartition
> ourselves instead of relying on the reset of per-tuple context to take
> care of it.  That's because some of the structures that ExecFindPartition
> assigns the allocated memory to are cleaned up at the end of the query, by
> when it's too late to try to release per-tuple memory.  So, the patch I
> ended up with is slightly bigger than simply adding a
> MemoryContextSwitchTo() call at the beginning of ExecFindPartition.

Yeah, that stuff looks a bit brittle.  I wish I had an idea on how to
make it less so. Thanks for taking care of that.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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