How to prevent very very large ccaches?

Nicolas Williams Nicolas.Williams at
Wed Jun 19 12:42:28 EDT 2002

On Tue, Jun 18, 2002 at 06:55:25PM -0400, Ken Raeburn wrote:
> Another thing to look at in the short term would be the stdio version
> of the ccache code.  Since it uses buffering, it wouldn't make nearly
> as many i/o calls.  Currently it's turned on by using "STDIO:" instead
> of "FILE:", but really I think it should be an implementation detail
> which one of the two is used for "FILE:" since AFAIK the contents
> should be the same regardless of the means used to access the disk
> file.

[You can't just turn on STDIO - that requires a patch I just posted.]

Given that patch the improvement I see of using STDIO over FILE is
tremendous. First off, my 20-at-a-time mass kvno run barely dents the load
average now. Second, on a quiet system, the difference between STDIO and
FILE, when using a very large ccache (1000 entries) is a FACTOR of TWO
(and a factor of TEN when using a ccache half that size).

I was using both of the patches I've posted when I got the results
mentioned above.


All of which begs the question: why not make STDIO be the default
ccache type?

I did not expect the difference of impact on load average between FILE
and STDIO in my tests. I'm not sure how to explain that - in both cases
the ccache was being locked only once during the ccache search, and in
both cases I was using the kvno command to keep all other overhead low.

> Ken


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