On Mon, Aug 9, 2010 at 12:31 PM, Bruce Momjian <br...@momjian.us> wrote: > Bruce Momjian wrote: >> > With our process-based design, the default is private memory (i.e. not >> > shared). If you need shared memory, you must specify a certain amount in >> > advance. That chunk of shared memory then is reserved and can't ever be >> > used by another subsystem. Even if you barely ever need that much shared >> > memory for the subsystem in question. >> >> Once multiple threads are using the same local memory, you have the same >> issues of being unable to resize it because repalloc can change the >> pointer location. > > 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. -- 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
