From: Daira Hopwood Date: Tue, 19 May 2015 23:13:47 +0000 (+0100) Subject: remote-to-local-sync.rst: Conflict Detection and Resolution WIP X-Git-Url: https://git.rkrishnan.org/vdrive/nxhtml.html?a=commitdiff_plain;h=20f156b95766c47be3b67c04b8782157a0e92265;p=tahoe-lafs%2Ftahoe-lafs.git remote-to-local-sync.rst: Conflict Detection and Resolution WIP Signed-off-by: Daira Hopwood --- diff --git a/docs/proposed/magic-folder/remote-to-local-sync.rst b/docs/proposed/magic-folder/remote-to-local-sync.rst index 63ece7f5..eeabc15c 100644 --- a/docs/proposed/magic-folder/remote-to-local-sync.rst +++ b/docs/proposed/magic-folder/remote-to-local-sync.rst @@ -244,17 +244,37 @@ each file encodes the full subpath of that file relative to the Magic Folder. -*Conflict detection* +Conflict Detection and Resolution +--------------------------------- -there are several kinds of dragon [*] +In our discussion of design issues for conflict detection and resolution, +we classified various problems as "dragons", which as a convenient +mnemonic we have named after the five classical Greek elements +(Earth, Air, Water, Fire and Aether). -earth dragons: write/download and read/download collisions +*Glossary* + +Write: a modification to a local filesystem object by a client +Read: a read from a local filesystem object by a client +Upload: an upload of a local object to the Tahoe-LAFS file store +Download: a download from the Tahoe-LAFS file store to a local object +Pending notification: a local filesystem change that has been detected +but not yet processed. + +*Earth Dragons: write/download and read/download collisions* + +Suppose that Alice changes the file ``foo`` locally, concurrently +with Alice's Magic Folder client writing a version of ``foo`` that +it has downloaded in response to a remote change. + +An important constraint on the design is that on Windows, it is +not possible to rename a file to the same name as an existing +file in that directory. -alice changes 'foo' locally while alice's gateway is writing 'foo' -locally (in response to a remote change) +Without this constraint, it would be possible to use the following +common technique for implementing "atomic" writes on Unix: -alice's gateway -* writes a temporary file foo.tmp +* Alice's Magic Folder client writes a temporary file ``foo.tmp`` * if 'foo' is clean, i.e. there are no pending notifications, it moves foo.tmp over foo [FIXME: if we want to preserve old versions then it should rename the old version first; see below]