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From Apache subversion Wiki <comm...@subversion.apache.org>
Subject [Subversion Wiki] Update of "MoveDev/MovesInFSFS" by JulianFoad
Date Wed, 11 Sep 2013 14:21:03 GMT
Dear Wiki user,

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The "MoveDev/MovesInFSFS" page has been changed by JulianFoad:
https://wiki.apache.org/subversion/MoveDev/MovesInFSFS

New page:
A specification for changes needed in FSFS and the FS API in order to support moves.

See also the specification of the semantics of moves:  MoveDev/MoveDev#Move_Semantics.

=== FS API ===
These new APIs are required:

 1. A way to find what has moved between two repository trees.          (In the repos layer,
responding to the "report", this   needs to be  a comparison between a mixed-revision state
and a  single-revision  tree.)
 1. A way to record moves during a commit.

==== 1. Query ====
New query API to find the same node-line in another revision: See under “Commit Editor and
Query Functions (FSFS)”.

The form of the query API could vary from the small scale such as querying the path at which
a given node-line-id lives in a particular  revision, to the large scale such as asking for
all the moves between  a given pair of revisions across the whole versioned tree.  The form
 suggested here is at an intermediate level: children of a directory.

 * Given two versioned directories, DIR1@REV1 and DIR2@REV2     (REV1 != REV2),  return a
list of (NAME1, NODE-LINE-ID, NAME2)  tuples containing each  node that is an immediate child
of DIR1@REV1    and/or of DIR2@REV2 and  is moved in REV2 relative to REV1.  In a       given
entry, NAME1 or NAME2  is null if the node moved into DIR2 or     out of DIR1 respectively.

That form reports renames directly and enables the caller to build up a mapping of cross-directory
moves by combining the results of multiple  queries.

Since that form only looks at a directory's children, we will also need  a single-node query.
 It could be in this form:

 * Given an existing node PATH1@REV1 and an existing revision   REV2, return  PATH2 at which
the same node-line lives in REV2, or       null if it does not.

==== 2. Commit ====
The following new method is needed:

 * svn_fs_move(svn_fs_root_t *root, from_path, to_path).        Similar to copy and delete,
except the copy will keep the same  (node-id, copy-id) as its source.  'root' must be the
root of a         transaction.

=== FSFS ===
Changes needed to extend FSFS format 6 (or 7?).

 * A lazy child of a copied node always gets a new copy-id,     never the copy-id of its parent,
when un-lazified.
  * ''Is'''' that ''''correct,'''' ''''Brane?''
 * New FS vtable methods to implement the interfaces defined in         the 'FS' section.
 * 'changes' list - record as a 'move'
 * Adjust implementation of existing query APIs to report moves         as copy-and-delete,
for back-compat.
 * (Possibly) A mechanism to flag whether move-aware semantics  are in use.

==== Flag Move-Aware Semantics ====
Consider whether we need to identify move-aware revisions as such.  This might be a single
flag for the whole repository (perhaps a format upgrade), or a cut-off revision after which
all further revisions are move-aware, or a flag per revision identifying whether a move-aware
client made the commit.

The purpose of this information would be to be able to know explicitly that copy + delete
does '''not''' mean 'move' in those commits.  Is this distinction necessary?  How would the
information be used?  (Client side?  Server side?)  What are the pros and cons?

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