Robert Haas wrote: > On Mon, Aug 9, 2010 at 11:02 AM, Bruce Momjian <br...@momjian.us> wrote: > > I am not sure threads would greatly help us. ?The major problem is that > > all of our our structures are currently contiguous in memory for quick > > access. ?I don't see how threading would help with that. ?We could use > > realloc(), but we can do the same in shared memory if we had a chunk > > infrastructure, though concurrent access to that memory would hurt us in > > either threads or shared memory. > > > > Fundamentally, recreating the libc memory allocation routines is not > > that hard. ?(Everyone has to detach from the shared memory segment, but > > they have to stop using it too, so it doesn't seem that hard.) > > I actually don't think that's true. The advantage (and disadvantage) > of using threads is that everything runs in one address space. So you > just allocate more memory and everyone immediately sees it. In a > process environment, that's not the case: to expand or shrink the size > of the shared memory arena, everyone needs to explicitly change their > own mapping.
You can't expand the size of malloc'ed memory --- you have to call realloc(), and then you effectively get a new pointer. Shared memory has a similar limitation. If you allocate shared memory in chunks so you don't need to change the location, you are effectively doing another malloc(), like you would in a threaded process. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
