On Tue, Jun 17, 2014 at 4:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> We could do better by accounting for memory usage ourselves, inside
>> the memory-context system, but that'd probably impose some overhead we
>> don't have today.
>
> Hm. We could minimize the overhead if we just accounted for entire
> malloc chunks and not individual palloc allocations. That would make
> the overhead not zero, but yet probably small enough to ignore.
Yeah, although it might expose more details of aset.c's allocation
behavior than we want users to have to know about.
> Another idea would be to do the enforcement ourselves by means of
> measuring the change in "sbrk(0)"'s reported value since startup, which we
> could check whenever, say, we're about to request a large malloc chunk in
> aset.c. I'm not sure about the cost of that function though, nor about
> whether this measurement method is meaningful in modern systems.
I wouldn't like to count on that method. I believe some malloc()
implementations implement large allocations via mmap().
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
