Hi, Wu,

Wu Fengguang wrote:

>>>In adaptive readahead, the context based method may be of particular
>>>interest to postgresql users. It works by peeking into the file cache
>>>and check if there are any history pages present or accessed. In this
>>>way it can detect almost all forms of sequential / semi-sequential read
>>>patterns, e.g.
>>>     - parallel / interleaved sequential scans on one file
>>>     - sequential reads across file open/close
>>>     - mixed sequential / random accesses
>>>     - sparse / skimming sequential read
>>>
>>>It also have methods to detect some less common cases:
>>>     - reading backward
>>>     - seeking all over reading N pages

Gread news, thanks!

> This call will disable readahead totally for fd:
>         posix_fadvise(fd, any, any, POSIX_FADV_RANDOM);
> 
> This one will reenable it:
>         posix_fadvise(fd, any, any, POSIX_FADV_NORMAL);
> 
> This one will enable readahead _and_ set max readahead window to
> 2*max_readahead_kb:
>         posix_fadvise(fd, any, any, POSIX_FADV_SEQUENTIAL);

I think that this is an easy, understandable and useful interpretation
of posix_fadvise() hints.


Are there any rough estimates when this will get into mainline kernel
(if you intend to submit)?

Thanks,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org

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