Re: shmget error text reports funny max_connections numbers

I have applied a patch to improve shared memory failure reporting,
attached.  We no longer report actual parameter _values_ and suggest
that other parameters might also cause such failures.

---------------------------------------------------------------------------

Alvaro Herrera wrote:
> Excerpts from Robert Haas's message of jue oct 14 21:36:48 -0300 2010:
> > On Wed, Oct 13, 2010 at 2:39 PM, Peter Eisentraut <peter_e@gmx.net> wrote:
> > > Since MaxBackends is actually max_connections + autovacuum_max_workers +
> > > 1, when you get an error message from shmget() it will tell you
> > >
> > > "reduce ... its max_connections parameter (currently 104)"
> > >
> > > when you actually set
> > >
> > > max_connections = 100
> > >
> > > This looks a bit silly.
> > >
> > > Should we just make the error messages report MaxBackends -
> > > autovacuum_max_workers - 1, or is it worthwhile calling out
> > > autovacuum_max_workers separately?
> >
> > I suppose there are other reasons we could run out of shared memory,
> > too.  max_locks_per_transaction, for example.  It might be good to
> > revise the wording of the message so as to suggest that these are only
> > some of the possible causes.
>
> Agreed.  Something like "reduce one or more of the following parameters:
> shared_buffers (currently NN), max_connections (currently NN),
> autovacuum_max_workers (currently MM),
>
> I also suggest that it would be good to revise these things so that
> sentences within those monstruous paragraphs can be translated
> separately.  Maybe changing the ErrorData stuff so that there can be
> more than one errhint field?  If that's too much trouble, perhaps having
> "%s. %s. %s. %s" as the first errhint parameter, and have each sentence
> be its own translatable unit.
>
> I also just noticed that we use stars for emphasis here, "This error
> does *not* mean..." which is maybe too cute.
>
> --
> Álvaro Herrera <alvherre@commandprompt.com>
> The PostgreSQL Company - Command Prompt, Inc.
> PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index aece026..aba6fa8 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -153,25 +153,25 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
           "segment exceeded your kernel's SHMMAX parameter.  You can either "
                          "reduce the request size or reconfigure the kernel with larger SHMMAX.  "
                   "To reduce the request size (currently %lu bytes), reduce "
-               "PostgreSQL's shared_buffers parameter (currently %d) and/or "
-                         "its max_connections parameter (currently %d).\n"
+                       "PostgreSQL's shared memory usage, perhaps by reducing shared_buffers"
+                         "or max_connections.\n"
                          "If the request size is already small, it's possible that it is less than "
                          "your kernel's SHMMIN parameter, in which case raising the request size or "
                          "reconfiguring SHMMIN is called for.\n"
         "The PostgreSQL documentation contains more information about shared "
                          "memory configuration.",
-                         (unsigned long) size, NBuffers, MaxBackends) : 0,
+                         (unsigned long) size) : 0,
                  (errno == ENOMEM) ?
                  errhint("This error usually means that PostgreSQL's request for a shared "
                    "memory segment exceeded available memory or swap space, "
                          "or exceeded your kernel's SHMALL parameter.  You can either "
                          "reduce the request size or reconfigure the kernel with larger SHMALL.  "
                   "To reduce the request size (currently %lu bytes), reduce "
-               "PostgreSQL's shared_buffers parameter (currently %d) and/or "
-                         "its max_connections parameter (currently %d).\n"
+                       "PostgreSQL's shared memory usage, perhaps by reducing shared_buffers"
+                         "or max_connections.\n"
         "The PostgreSQL documentation contains more information about shared "
                          "memory configuration.",
-                         (unsigned long) size, NBuffers, MaxBackends) : 0,
+                         (unsigned long) size) : 0,
                  (errno == ENOSPC) ?
                  errhint("This error does *not* mean that you have run out of disk space. "
                          "It occurs either if all available shared memory IDs have been taken, "
@@ -179,11 +179,10 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
           "or because the system's overall limit for shared memory has been "
                  "reached.  If you cannot increase the shared memory limit, "
           "reduce PostgreSQL's shared memory request (currently %lu bytes), "
-            "by reducing its shared_buffers parameter (currently %d) and/or "
-                         "its max_connections parameter (currently %d).\n"
+                   "perhaps by reducing shared_buffers or max_connections.\n"
         "The PostgreSQL documentation contains more information about shared "
                          "memory configuration.",
-                         (unsigned long) size, NBuffers, MaxBackends) : 0));
+                         (unsigned long) size) : 0));
     }

     /* Register on-exit routine to delete the new segment */