On Mon, Aug 9, 2010 at 2:50 PM, Bruce Momjian <br...@momjian.us> wrote: > Robert Haas wrote: >> On Mon, Aug 9, 2010 at 2:33 PM, Bruce Momjian <br...@momjian.us> wrote: >> >> > Let me be more concrete. ?Suppose you are using threads, and you want to >> >> > increase your shared memory from 20MB to 30MB. ?How do you do that? ?If >> >> > you want it contiguous, you have to use realloc, which might move the >> >> > pointer. ?If you allocate another 10MB chunk, you then have shared >> >> > memory fragments, which is the same as adding another shared memory >> >> > segment. >> >> >> >> You probably wouldn't do either of those things. ?You'd just allocate >> >> small chunks here and there for whatever you need them for. >> > >> > Well, then we do that with shared memory then --- my point is that it is >> > the same problem with threads or processes. >> >> Well, I think your point is wrong, then. :-) >> >> It's not the same at all. If you have a bunch of threads in one >> address space, "shared" memory is really just process-local. You can >> grow the total amount of allocated space just by calling malloc(). >> With our architecture, you can't. > > You effectively have to add infrastructure to add/remove shared memory > segments to match memory requests. It is another step, but it is the > same behavior.
That would be one way to tackle the problem, but there are difficulties. If we just created new shared memory segments at need, we might end up with a lot of shared memory segments. I suspect that would get complicated and present many management difficulties - which is why I'm so far of the opinion that we should try to architect the system to avoid the need for this functionality. I don't think it's going to be too easy to provide, short of (as Tom says) moving to the MySQL model of many threads working in a single process. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers