Re: [HACKERS] fork/exec for backend

On Sat, 24 Jan 1998, Bruce Momjian wrote:

> > On 24 Jan 1998, Goran Thyni wrote:
> >
> > > Fork on modern unices (linux and (a think) *BSD) cost
> > > almost nothing (in time and memory) thanks to COW (copy-on-write).
> > > Exec in expensive as it breaks COW.
> >
> >   Not so.  Modern Unixs will share executable address space between
> > processes.  So if you fork and exec 10 identical programs, they will share
> > most address space.
> >
> >   If you want to speed this up, link postgresql static.  This makes exec()
> > cost almost nothing too.  postgresql becomes its own best shared library.
> >
> >   Again, this only applies to "modern" systems, but FreeBSD definitely has
> > this behaviour.
>
> This is very OS-specific.  SunOS-style shared libraries do have a
> noticable overhead for each function call.  In fact, even though these
> are part of BSD44 source, BSDI does not use them, and uses a more crude
> shared library jump table, similar to SVr3 shared libraries because of
> the SunOS shared library overhead.

  Regardless on the method used, the dynamic executables need to undergo a
link step during exec().  Linking static reduces that.

> I think FreeBSD and Lunix use SunOS style shared libraries, often called
> dynamic shared libraries because you can change the function while the
> binary is running if you are realy careful.

  Linux uses ELF shared libraries.  I don't know how those work.

  I don't FreeBSD to have a high call overhead for dynamic libs at all.
Static executables just start faster thats all.

> --
> Bruce Momjian
> maillist@candle.pha.pa.us
>
>

Tom