[Twisted-Python] Re: Twisted 1.0.4 - Heavy search for `plugins.tml'

[Francois Pinard]

[Tommi Virtanen]
> [Francois Pinard]

> > [...] if the number of links of that directory -- itself -- is exactly
> > 2, we can conclude that it has no sub-directories, and that there
> > is nothing more to check for this one.

> The important thing is to make that optimization disabled if link count
> != 2.  That is, in any other case you really need to go through the
> stat calls.

If I remember well, GNU `find' keeps the link count for a given directory.
Every time it stats an entry which is a sub-directory, it decreases the
link count.  When the link count reaches 2, the loop is exited (provided
`stat' calls are only needed for directory recursion -- `find' sometimes
need them for other purposes).

> A Linux box with enough memory should have really good stat performance
> with a hot cache.  [...] But even Linux will suffer the same performance
> problems with a cold cache or too little RAM to cache much.

One may consider that Twisted may also be used on lesser Unices than
Linux -- I'm not going to name any! :-) -- where the performance hit might
hurt more.  As a good rule, I think one should not overly rely on various
systems' disk cache, and be on the parsimonious side while accessing disks.

-- 
François Pinard   http://www.iro.umontreal.ca/~pinard