lkml.org 
[lkml]   [2006]   [May]   [25]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateFri, 26 May 2006 13:14:04 +1000
FromNick Piggin <>
SubjectRe: [PATCH 00/33] Adaptive read-ahead V12
Jon Smirl wrote:

> On 5/25/06, Andrew Morton <akpm@osdl.org> wrote:
>
>> These are nice-looking numbers, but one wonders.  If optimising 
>> readahead
>> makes this much difference to postgresql performance then postgresql 
>> should
>> be doing the readahead itself, rather than relying upon the kernel's
>> ability to guess what the application will be doing in the future.  
>> Because
>> surely the database can do a better job of that than the kernel.
>>
>> That would involve using posix_fadvise(POSIX_FADV_RANDOM) to disable 
>> kernel
>> readahead and then using posix_fadvise(POSIX_FADV_WILLNEED) to launch
>> application-level readahead.
>
>
> Users have also reported that this patch fixes performance problems
> from web servers using sendfile(). In the case of lighttpd they
> actually stopped using sendfile() for large transfers and wrote a user
> space replacement where they could control readahead manually. With
> this patch in place sendfile() went back to being faster than the user
> space implementation.


Of course, that is something one would expect should be made to work 
properly
with the current readahead implementation.

I don't see Wu's patches getting in for a little while yet.

Reproducable test cases (preferably without a whole lot of network clients)
should get this proble fixed.

--

Send instant messages to your online friends http://au.messenger.yahoo.com 

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-05-26 05:16    [from the cache]
©2003-2008