> From: Thomas Munro [mailto:thomas.mu...@enterprisedb.com] > > Does Postgres provide a convenient way for one process to pass data to > > another using shared memory? > > 1. Look at ShmemInitStruct, ShmemInitHash (as in hash table), ShmemInitQueue > in storage/shmem.h. These use memory that is mapped at the same address in > every backend (process) which is convenient for sharing data structures with > internal pointers. The amount of memory available is fixed at cluster > startup however.
Thanks. That limit could be an issue. The notes in shmem.c are helpful. > 2. Look at dsm_XXX in storage/dsm.h. This subsystem provides segments of > memory that is "dynamic" in the sense that it is limited only by your > system's available virtual memory, but you have to explicitly attach these > segment in any backend that wants to access them by passing a handle around > and the memory may be mapped at any address in each backend, so you need to > work harder to build data structures that reference each other (using offsets > rather than pointers, that kind of thing). DSM segments won't work well if > you try to create large numbers of them, so you'll need to provide a way to > manage the space inside a smallish number of large chunks of DSM memory > yourself (this is a problem I'm working to fix by providing a general purpose > allocator backed by a bunch of DSM segments -- watch this space). LWLocks > (our usual lock primitive for cases where spinlocks are inappropriate) > currently don't work correctly inside DSM segments (this too will be fixed). I've now found this through the test_shm_mq sample. Looks like an answer, if quite a bit of machinery needed. Thanks for the pointers. Regards David M Bennett FACS Andl - A New Database Language - andl.org -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
