Re: [HACKERS] Advice wanted on backend memory management

Tom Lane wrote:
>
> I want to change hashjoin's use of a fixed-size overflow area for tuples
> that don't fit into the hashbucket they ought to go in. Since it's
> always possible for an improbably large number of tuples to hash into the
> same hashbucket, the overflow area itself can overflow; without the
> ability to recover from that, hashjoin is inherently unreliable.
> So I think this is an important thing to fix.
>
> To do this, I need to be able to allocate chunks of space that I will
> later want to give back all at once (at the end of a hash pass).
> Seems to me like a job for palloc and a special memory context ---
> but I see no way in mcxt.h to create a new memory context. How do
> I do that? Also, I'd want the new context to be a "sub-context" of

No way :(
StartPortalAllocMode could help but - portalmem.c:
/*
* StartPortalAllocMode
* Starts a new block of portal heap allocation using mode and limit;
* the current block is disabled until EndPortalAllocMode is called.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I'm unhappy with this allocation block stacking for quite long time :(

Try to pfree chunks "by hand".

Vadim