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Diffstat (limited to 'doc/legacy')
| -rw-r--r-- | doc/legacy/hacker-guide/write-behind.txt | 45 |
1 files changed, 0 insertions, 45 deletions
diff --git a/doc/legacy/hacker-guide/write-behind.txt b/doc/legacy/hacker-guide/write-behind.txt deleted file mode 100644 index 50b7d2a1d07..00000000000 --- a/doc/legacy/hacker-guide/write-behind.txt +++ /dev/null @@ -1,45 +0,0 @@ -basic working --------------- - - write behind is basically a translator to lie to the application that the write-requests are finished, even before it is actually finished. - - on a regular translator tree without write-behind, control flow is like this: - - 1. application makes a write() system call. - 2. VFS ==> FUSE ==> /dev/fuse. - 3. fuse-bridge initiates a glusterfs writev() call. - 4. writev() is STACK_WIND()ed upto client-protocol or storage translator. - 5. client-protocol, on receiving reply from server, starts STACK_UNWIND() towards the fuse-bridge. - - on a translator tree with write-behind, control flow is like this: - - 1. application makes a write() system call. - 2. VFS ==> FUSE ==> /dev/fuse. - 3. fuse-bridge initiates a glusterfs writev() call. - 4. writev() is STACK_WIND()ed upto write-behind translator. - 5. write-behind adds the write buffer to its internal queue and does a STACK_UNWIND() towards the fuse-bridge. - - write call is completed in application's percepective. after STACK_UNWIND()ing towards the fuse-bridge, write-behind initiates a fresh writev() call to its child translator, whose replies will be consumed by write-behind itself. write-behind _doesn't_ cache the write buffer, unless 'option flush-behind on' is specified in volume specification file. - -windowing ---------- - - write respect to write-behind, each write-buffer has three flags: 'stack_wound', 'write_behind' and 'got_reply'. - - stack_wound: if set, indicates that write-behind has initiated STACK_WIND() towards child translator. - - write_behind: if set, indicates that write-behind has done STACK_UNWIND() towards fuse-bridge. - - got_reply: if set, indicates that write-behind has received reply from child translator for a writev() STACK_WIND(). a request will be destroyed by write-behind only if this flag is set. - - currently pending write requests = aggregate size of requests with write_behind = 1 and got_reply = 0. - - window size limits the aggregate size of currently pending write requests. once the pending requests' size has reached the window size, write-behind blocks writev() calls from fuse-bridge. - blocking is only from application's perspective. write-behind does STACK_WIND() to child translator straight-away, but hold behind the STACK_UNWIND() towards fuse-bridge. STACK_UNWIND() is done only once write-behind gets enough replies to accomodate for currently blocked request. - -flush behind ------------- - - if 'option flush-behind on' is specified in volume specification file, then write-behind sends aggregate write requests to child translator, instead of regular per request STACK_WIND()s. - - |