Re: [HACKERS] Advice wanted on backend memory management

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From: Vadim Mikheev <vadim @ krs.ru> on 05/04/99 09:18 PM
To: Tom Lane <tgl @ sss.pgh.pa.us>@SMTP(at)EXCHANGE
cc: pgsql-hackers @ postgreSQL(dot)org(at)SMTP@EXCHANGE
Subject: 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