[Libreoffice] ccache support

[Christian Lohmaier]

Hi *,

On Tue, Aug 9, 2011 at 8:58 PM, Terrence Enger <tenger at iseries-guru.com> wrote:
> On Mon, 2011-08-08 at 11:40 +0200, Christian Lohmaier wrote:
>>
>> Not true either. Default ccache size is 1GB, and that is enough when
>> you focus on one branch. (a build uses less than 500MB)
>
> Just a note about what I have observed, for anybody who
> happens to care.
>
>
>    cache directory                     /home/terry/.ccache
>    cache hit (direct)                  6158
>    cache hit (preprocessed)              37
>    cache miss                         11986
> [...]
>    files in cache                     30789
>    cache size                           4.1 Gbytes
>    max cache size                      10.0 Gbytes
>
> This makes me really glad that I set a max cache size larger
> than the default 1 GB,

So you showed some irrelevant numbers, at least for the current topic.
Your cache is filled with other stuff already, not with just the files
from one single build.
And of course ccache will happily use whatever size is available
before it starts to expire old files.

But yes, If you build with debug symbols, you need larger cache size.
The <500MB for a build was referring to product builds, without any
debugging options.

> For comparison, after I had completed several non-product
> builds of OpenOffice, my cache statistics looked like ...
>
>    cache directory                     /media/2ced347d-3cdc-49f5-956d-099d36784957/terry/OOo_hacking/SRC_DIR_ccache
>    cache hit (direct)                     0
>    cache hit (preprocessed)           15499
>    cache miss                         14993

That is a rather bad hit ratio - something between 5:1 and 10:1 when
building often would be what I expect. 1:1 is when you build versions
that did have lots of changes in between.
And no direct hits? Did you disable it?

Norbert's ratio is of course when you build multiple times a day, so
might not be that representative either :-)

But you see that the cache-size doesn't need to be big to get hits.
When you stay on one branch, then the files that didn't match won't
match in future, so no need to keep them around, they can be expired.
When you switch back and forth in history and between different
branches, you should consider using different cache-directories (when
you build the other branches seldomly compared to your main tree), or
use a bigger size (if the other branch gets build regularly, and thus
the files in the cache are touched and thus not considered candidates
for expiry).

>    max files                         100000

Any reason why you set a limit on the number of files?

ciao
Christian