BRANCH-README - subversion - Git at Google

 Pristines-on-Demand
 -------------------

 The purpose of this branch is to try to make the text-bases in the working
 copy optional [1][2].


 Description of the approach:
 ----------------------------

 The core idea is that we start to maintain the following invariant: only the
 modified files have their pristine text-base files available on the disk.

 - To avoid having to access the text-base, the "is the file modified?" check
   is performed by calculating the checksum of a file and comparing that to
   what's recorded in the working copy.

 - A text-base of the unmodified file is the file itself, appropriately
   detranslated.

 - To get into the appropriate state at the beginning of the operation, we walk
   through the current text-base info in the db and check if the corresponding
   working files are modified.  The missing text-bases are fetched using the
   svn_ra layer.  The operations also include a final step during which the
   no longer required text-bases are removed from disk.

 - The operations that don't need to access the text-bases (such as "svn ls"
   or the updated "svn st") do not perform this walk and do not synchronize
   the text-base state.


 For the production-ready state, it would probably make sense to also:
 ---------------------------------------------------------------------

  1. Complete the work on ^/subversion/branches/multi-wc-format so that the
     client would work with both the new and old working copy formats, for
     a seamless user experience and better compatibility.

     (Done in r1897946)

  2. For the new working copy format, incorporate a switch to a different
     checksum type without known collisions instead of SHA-1.

 3. Fix the minor issues written down as TODOs in the code.


 References:
 -----------

 [1] https://issues.apache.org/jira/browse/SVN-525
 [2] https://lists.apache.org/thread.html/r40aa795b9e0c1aabb392c43b64e540432a31e22d8b0d9de7202b4950%40%3Cdev.subversion.apache.org%3E
	Pristines-on-Demand
	-------------------

	The purpose of this branch is to try to make the text-bases in the working
	copy optional [1][2].


	Description of the approach:
	----------------------------

	The core idea is that we start to maintain the following invariant: only the
	modified files have their pristine text-base files available on the disk.

	- To avoid having to access the text-base, the "is the file modified?" check
	is performed by calculating the checksum of a file and comparing that to
	what's recorded in the working copy.

	- A text-base of the unmodified file is the file itself, appropriately
	detranslated.

	- To get into the appropriate state at the beginning of the operation, we walk
	through the current text-base info in the db and check if the corresponding
	working files are modified. The missing text-bases are fetched using the
	svn_ra layer. The operations also include a final step during which the
	no longer required text-bases are removed from disk.

	- The operations that don't need to access the text-bases (such as "svn ls"
	or the updated "svn st") do not perform this walk and do not synchronize
	the text-base state.


	For the production-ready state, it would probably make sense to also:
	---------------------------------------------------------------------

	1. Complete the work on ^/subversion/branches/multi-wc-format so that the
	client would work with both the new and old working copy formats, for
	a seamless user experience and better compatibility.

	(Done in r1897946)

	2. For the new working copy format, incorporate a switch to a different
	checksum type without known collisions instead of SHA-1.

	3. Fix the minor issues written down as TODOs in the code.


	References:
	-----------

	[1] https://issues.apache.org/jira/browse/SVN-525
	[2] https://lists.apache.org/thread.html/r40aa795b9e0c1aabb392c43b64e540432a31e22d8b0d9de7202b4950%40%3Cdev.subversion.apache.org%3E