Robert Haas wrote: > 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.
You could allocate shared memory in chunks and then pass that out to requestors, the same way sbrk() does it. -- 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
