Re: [HACKERS] Compile timing

> > Not sure why -j2 is not faster than normal -j...
> 
> I was just looking at this a little while ago at work. It is not
> faster because gmake does not propagate the "-j2" flag to submakes, on
> the (correct) theory that you might get a geometrically growing system
> load, rather than just keeping two makes running through all the
> subdirectories.
> 
> This is the behavior of "-j", unless you specify it without a numeric
> parameter, in which case it *does* allow parallel submakes.
> 
> The first time I tried "-j", I did it without reading the man pages
> and without specifying a numeric parameter. It did a magnificent job
> of bringing down my system trying to build ACE/TAO, a *large* Corba
> package. Chewed up all of real memory, then all of swap; not sure if I
> ran out of process slots or memory first but it wasn't pretty. It was
> *very* fast though :)

I just tried:
gmake MAKE="gmake -j 2"

and that fails because we can't parellize because we need certain
includes.  I can't seem to get the proper includes to happen before it
fails.

I am getting:

gmake[3]: Entering directory
`/var/local/src/pgsql/CURRENT/pgsql/src/backend/access/common'
gmake[3]: *** No rule to make target `hash/SUBSYS.o'.  Stop.
gmake[3]: Leaving directory `/var/local/src/pgsql/CURRENT/pgsql/src/backend/acce

Seems it is trying to complete the linking before the compiles are done.
If I made -j2 happen only in directories with compiles, and not outside,
that might fix it.  The propogation of -j2 to subdirectories and the
exponential explosion is exactly what happens.

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