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 <wahu0315...@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.ga...@brainsware.org URL: http://brainsware.org/
