SHMSEG definition - Mailing list pgsql-hackers

From Michael Brusser
Subject SHMSEG definition
Date
Msg-id DEEIJKLFNJGBEMBLBAHCOEHFDGAA.michael@synchronicity.com
Whole thread Raw
In response to Re: backend/parser compile prob  (Patrick Welche <prlw1@newn.cam.ac.uk>)
List pgsql-hackers
Can somebody clarify for me the requirement for the SHMSEG kernel parameter,
please.

The Postgres doc says:

SHMSEG - Maximum number of shared memory segments per process        only 1 segment is needed, but the default is much
higher

I was trying to calculate the kernel parameters for running a number
of Postgres servers on Solaris, and something did not work.

Having Postgres running I executed ipcs. It shows that while Postgres is
taking
only one segment, the number of attachments is 7. This I think refers to the
number
of processes spawned by postmaster at that time.

Solaris docs describe SHMSEG as  "Limit on the number of shared memory segments   that any one process can create"

Now run this:
sysdef | grep SHMSEG
->   50  max attached shm segments per process (SHMSEG)

I suppose there's a distinction between "can create" and "can attach to".
Looks like the manual and output of sysdef are not very consistent.

I am worried that maybe (on Solaris) SHMSEG should be set with respect
to number of connections, rather than number of servers.

Thank you,
Mike.




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