Question about Shared memory and PG

Hi,

Bit of background:

PGPOOL (V8 with PG 803) talking to 2 x Red Hat ES4, HP DL 380s with 2Gb
RAM and twin CPUs running PG 807

Last night PGPOOL alerted our OOH on call guy saying that it could
communicate with the second DB server

In the PG log file the errors were:

2006-08-03 21:49:18 BST FATAL: invalid frontend message type 50

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

2006-08-03 21:49:18 BST LOG: unexpected EOF on client connection

The DB was up and so it was shutdown and a restart was attempted but
failed with:

could not create shared memory segment: Invalid argument - (pg.conf
shared_buffers set to 750Mb)

Anyway it was decided to leave it until the morning.

What we realised this morning was that the SHMMAX param was set to 512M
and hence that's why the DB wouldn't start.

What we think has happened is that SHMMAX has been reset (when and by
whom we don't yet know) from 1024Mb to 512Mb.

Basically my question(s) is/are what happens to PG when this memory
param is modified on the fly, could it explain the above PG log errors?

Initial experiments certainly allow the param to be modified while PG is
running without any obvious side effects though possibly over time it
could cause a problem - DB & box have been running since April

The network logs at the time being checked also.

Any input on this would be much appreciated

Regards

Nigel

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