Re: Safe memory allocation functions

On Tue, Jan 13, 2015 at 10:10 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> However, there is a larger practical problem with this whole concept,
> which is that experience should teach us to be very wary of the assumption
> that asking for memory the system can't give us will just lead to nice
> neat malloc-returns-NULL behavior. Any small perusal of the mailing list
> archives will remind you that very often the end result will be SIGSEGV,
> OOM kills, unrecoverable trap-on-write when the kernel realizes it can't
> honor a copy-on-write promise, yadda yadda. Agreed that it's arguable
> that these only occur in misconfigured systems ... but misconfiguration
> appears to be the default in a depressingly large fraction of systems.
> (This is another reason for "_safe" not being the mot juste :-()

I don't really buy this. It's pretty incredible to think that after a
malloc() failure there is absolutely no hope of carrying on sanely.
If that were true, we wouldn't be able to ereport() out-of-memory
errors at any severity less than FATAL, but of course it doesn't work
that way. Moreover, AllocSetAlloc() contains malloc() and, if that
fails, calls malloc() again with a smaller value, without even
throwing an error.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company