Обсуждение: build times

I have been investigating some build performance issues, and trying to 
narrow down causes of slowness, and observed an odd effect, which was 
suggested by a huge time difference between building from git and 
building from a tarball.

If I do
    make -C src/port all

and then wait 10 seconds or so and do
    make -j 3

or even just plain
    make

the build finishes much much faster (like 1m vs 5m) than if I had not 
run the first command.

I have seen this on a Fedora VM (VirtualBox, W7 host, Athlon II X2) and 
a ScientificLinux 6 machine (dual quad xeon E5620).

The setup is a vpath build configured thus:
   ../pgsql/configure --enable-cassert --enable-debug   --enable-integer-datetimes --with-perl --with-python --with-tcl
 --with-krb5 --with-includes=/usr/include/et --with-openssl   --with-ldap --with-libxml --with-libxslt
 


Can anyone with a bit more make-fu than I have suggest why this should 
be so? Can we tweak the make files so hacks like this aren't required to 
get a fast build? Can anyone replicate this odd result?

cheers

andrew

Andrew Dunstan <andrew@dunslane.net> writes:
> I have been investigating some build performance issues, and trying to 
> narrow down causes of slowness, and observed an odd effect, which was 
> suggested by a huge time difference between building from git and 
> building from a tarball.

> If I do
>      make -C src/port all
> and then wait 10 seconds or so and do
>      make -j 3
> or even just plain
>      make

> the build finishes much much faster (like 1m vs 5m) than if I had not 
> run the first command.

Can't reproduce that here.  What I do notice on a Fedora 14 machine is
that ccache seems to be enabled by default, ie you get caching even when
you just say "gcc", and that makes a huge difference in build times.
I see 70 seconds after "rm -rf ~/.ccache", versus 4 seconds with it
fully populated.  Building src/port first saves nothing in either
starting state.

I wonder whether your experiments got affected by something similar.
        regards, tom lane

On 10/02/2011 05:25 PM, Tom Lane wrote:
> Andrew Dunstan<andrew@dunslane.net>  writes:
>> I have been investigating some build performance issues, and trying to
>> narrow down causes of slowness, and observed an odd effect, which was
>> suggested by a huge time difference between building from git and
>> building from a tarball.
>> If I do
>>       make -C src/port all
>> and then wait 10 seconds or so and do
>>       make -j 3
>> or even just plain
>>       make
>> the build finishes much much faster (like 1m vs 5m) than if I had not
>> run the first command.
> Can't reproduce that here.  What I do notice on a Fedora 14 machine is
> that ccache seems to be enabled by default, ie you get caching even when
> you just say "gcc", and that makes a huge difference in build times.
> I see 70 seconds after "rm -rf ~/.ccache", versus 4 seconds with it
> fully populated.  Building src/port first saves nothing in either
> starting state.
>
> I wonder whether your experiments got affected by something similar.
>
>             

Yes, possibly, although SL6 (which is an RHEL clone) doesn't have ccache 
by default. I'm not sure what happened there, as now I can't reproduce 
it either.

Sorry for the noise.

cheers

andrew