Re: Multiple Indexing, performance impact

Lincoln Yeoh <lyeoh@pop.jaring.my> writes:

Why is SHMMAX so low on some O/Ses?

Historical artifact, I think: the SysV IPC code was developed on
machines that were tiny by current standards. Unfortunately, vendors
haven't stopped to review their kernel parameters and scale them up
appropriately.

regards, tom lane

At 05:56 PM 22-06-2001 -0400, Bruce Momjian wrote:

Bruce Momjian <pgman@candle.pha.pa.us> writes:
Since 64 is already too much to let 7.1 fit in SHMMAX = 1MB, I think
the original rationale for using 64 is looking pretty broken anyway.
Comments?

BSD/OS has a 4MB max but we document how to increase it by recompiling
the kernel. Maybe if we fail the startup we can tell them how to
decrease the buffers in postgresql.conf file. Seems quite clear.

Why is SHMMAX so low on some O/Ses? What are the advantages?

My guess is it's a minimum vs median/popular situation. Get the same thing
looking at the default www.kernel.org linux kernel settings vs the Redhat
kernel settings.

I'd personally prefer the popular situation. But would that mean the
minimum case can't even boot up to recompile? Maybe the BSD guys should
ship with two kernels then. FreeBSD esp, since it's easy to recompile the
kernel, just do two, during installation default to "Regular", with an
option for "Tiny".

It's more fair that the people trying the extraordinary (16MB 386) should
be the ones doing the extra work.

I think the problem is that with a default-sized kernel, the little guys
couldn't even boot the OS. Also, some of the OS's hard-wire things into
the kernel for performance reasons.

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