Attaching and using the Postgres shared memory segment

to look into an idea I currently have I need (and implemented) a new
piece of memory that resides in (Postgres) shared memory. My data
structures are in place an the new database seems running fine. Even
under high load :-)

Since these data structures are for collecting information I was able
to create a new function that retrieves its information from these
data structures and returns them as a result from a query.

However this is too intrusive. Since everything is in shared memory it
should be possible for an external, yet to be created, process to
attach to the shared memory segment (read only mode only) to collect
these data structures.

However, when I read the source I feel a little stuck. Kind of chicken
and egg situation perhaps.

I have the address mapping of the shared memory (doing stuff on
Solaris only). I can pass this information to InitShmemAccess (ipc/
shmem.c). There is however a missing settting for ShmemIndex. This
one can be initialsed by calling InitShmemIndex(). The only thing that
makes me wonder is its need to use ShmemIndexLock. Although this is
just an enum, and therefore an index in some array created in
CreateLWLock (lwlock.c). I do not see how I can get access to this
lock. Is it "just" there since obviously the whole Postgres shared
memory is allocated, initialised and likely already heavily used.
Do the locks map to a "well know address" so I can do without further
in process initialisation? Or is there another routine (or two ...)
that I need to call in order to make things working.

Advise on how to proceed or pointers to docs in which this stuff is
explained are highly appreciated.

Thanks
Paul.

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Paul van den Bogaard Paul(dot)vandenBogaard(at)sun(dot)com
ISV-E -- ISV Engineering, Opensource Engineering group

Sun Microsystems, Inc phone: +31
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