The logic structure of class Part in iocore/cache/P_CachePart.h

[张练 <wa...@gmail.com>]

    I have some questions with the design of class Part. I think the Part is
divided into several Segments, and each Segments contain 2^16 buckets, and
each buckets contain 4 object. In default, every object's size is
8000(proxy.config.cache.min_average_object_size), and each object has an
opposite element Dir to store their position in Part. The member named
header in Part, whose type is PartHeaderFooter, has an array member freelist
used to store each Segment's position message, and with these message, Part
use some macro, such as part_dirlen and so on, to find every object's exact
position.
    But i can't understand the following members' usage:
    What are the meaning of method evacuateWrite and aggWrite? And what is
the logic of the implement of these methods?

-- 
Best regards,
mohan_zl

Re: The logic structure of class Part in iocore/cache/P_CachePart.h

[Igor Galić <i....@brainsware.org>]

John,

do you mind if we put this into the SDK docs like this, or do you
think it needs some touching up?

----- Original Message -----
> Each bucket points to a linked list of directory entrys (Dir) which
> point
> to  "fragment"s which is a contiguous piece of an "object" or
> "document".
> 
> For performance reasons (to take advantage of the L1 cache) Dir
> entries
> allocated for a bucket are taken first from the other 3 entries in
> the
> bucket.
> 
> Each "fragment" (part of an object up to 2MB) has a Dir entry.  The
> 8K
> figure is a lower bound on the size of objects and hence the number
> of
> fragments and therefore the number of Dir entries the cache must
> provide for.
> 
> The freelist in Part is used to store the linked list of free Dir
> entries
> within a segment.
> 
> The method evacuateWrite is used to evacuate documents when the
> write_pos is about to write over a document.  The cache is organized
> like a cyclone buffer or a log-based file system and evacuateWrite is
> part of the "cleaner".
> 
> The method "aggWrite" collects all the pending fragments and groups
> them into a single write (for seek efficiency) of up to 4MB.  It then
> does the write and notifies the CacheVC's (some of which might
> be doing evacuations) when the write is complete.
> 
> john
> 
> 
> On Tue, Mar 8, 2011 at 4:25 AM, 张练 <wa...@gmail.com> wrote:
> 
> >    I have some questions with the design of class Part. I think the
> >    Part is
> > divided into several Segments, and each Segments contain 2^16
> > buckets, and
> > each buckets contain 4 object. In default, every object's size is
> > 8000(proxy.config.cache.min_average_object_size), and each object
> > has an
> > opposite element Dir to store their position in Part. The member
> > named
> > header in Part, whose type is PartHeaderFooter, has an array member
> > freelist
> > used to store each Segment's position message, and with these
> > message, Part
> > use some macro, such as part_dirlen and so on, to find every
> > object's exact
> > position.
> >    But i can't understand the following members' usage:
> >    What are the meaning of method evacuateWrite and aggWrite? And
> >    what is
> > the logic of the implement of these methods?
> >
> > --
> > Best regards,
> > mohan_zl
> >
> 

-- 
Igor Galić

Tel: +43 (0) 664 886 22 883
Mail: i.galic@brainsware.org
URL: http://brainsware.org/

Re: The logic structure of class Part in iocore/cache/P_CachePart.h

[John Plevyak <jp...@acm.org>]

Each bucket points to a linked list of directory entrys (Dir) which point
to  "fragment"s which is a contiguous piece of an "object" or "document".

For performance reasons (to take advantage of the L1 cache) Dir entries
allocated for a bucket are taken first from the other 3 entries in the
bucket.

Each "fragment" (part of an object up to 2MB) has a Dir entry.  The 8K
figure is a lower bound on the size of objects and hence the number of
fragments and therefore the number of Dir entries the cache must
provide for.

The freelist in Part is used to store the linked list of free Dir entries
within a segment.

The method evacuateWrite is used to evacuate documents when the
write_pos is about to write over a document.  The cache is organized
like a cyclone buffer or a log-based file system and evacuateWrite is
part of the "cleaner".

The method "aggWrite" collects all the pending fragments and groups
them into a single write (for seek efficiency) of up to 4MB.  It then
does the write and notifies the CacheVC's (some of which might
be doing evacuations) when the write is complete.

john


On Tue, Mar 8, 2011 at 4:25 AM, 张练 <wa...@gmail.com> wrote:

>    I have some questions with the design of class Part. I think the Part is
> divided into several Segments, and each Segments contain 2^16 buckets, and
> each buckets contain 4 object. In default, every object's size is
> 8000(proxy.config.cache.min_average_object_size), and each object has an
> opposite element Dir to store their position in Part. The member named
> header in Part, whose type is PartHeaderFooter, has an array member
> freelist
> used to store each Segment's position message, and with these message, Part
> use some macro, such as part_dirlen and so on, to find every object's exact
> position.
>    But i can't understand the following members' usage:
>    What are the meaning of method evacuateWrite and aggWrite? And what is
> the logic of the implement of these methods?
>
> --
> Best regards,
> mohan_zl
>