work in progress: bidirectional sync

work in progress: bidirectional sync

Sunday, October 02, 2011 Pablo Santos distributed 6 Comments

I'm working on "bi-directional sync" which is one of the reasons behind the move to Plastic SCM 4.0.

What is it?

Simple: a way to sync a branch with another scm and handle conflicting changes.

I'm writing down a very initial session below:

Sync with Subversion - initial import

Here we go, first thing is to make myself admin of the repo due to a bug I still didn't fix on the import code (ouch!)

  $ cm setowner -user=pablo repserver:localhost:8084

Now launch the first sync, note I specify the branch in Plastic, the type of scm (svn, it could also be "tfs" now) and the scm url

  $ cm sync main@default@localhost:8084 svn svn://localhost
    Latest cset on foreign SCM: 6
    Changesets to pull
    1 - 01/10/2011 7:18:16 -  - trunk created
    2 - 01/10/2011 7:19:30 -  - initial code import
    3 - 01/10/2011 7:28:25 -  - hud.txt modified
    4 - 01/10/2011 7:30:28 -  - trunk created
    5 - 01/10/2011 8:00:04 -  - hello.txt added
    6 - 01/10/2011 8:03:00 -  - modified hello.txt

Now a second hack due to another bug I still didn't fix

  $ cm au pablo
    User pablo has been successfully activated

Then create a new workspace, update to get the code imported from SVN and so on

  $ cm mkwk plasticwk .
    Workspace plasticwk has been correctly created

  $ cm update .
    Copied c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\hello.txt

   $ cm ls
            01/10/2011 08:03 dir    br:/main#6         .
            01/10/2011 08:05 txt    br:/main#1         hello.txt

Make a change in Plastic and push it to SVN

Create a new file, checkin and push to SVN.

   $ echo bye > bye.txt

   $ cm add bye.txt
    The selected items are about to be added. Please wait ...
    Item bye.txt was correctly added

   $ cm ci -c="added bye.txt"
    The selected items are about to be checked in. Please wait ...
    Assembling checkin data
    Validating checkin data
    Uploading file data
    Uploaded 6 bytes of 6 bytes (100%)
    Confirming checkin operation
    Modified c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk
    Added c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\bye.txt
    Created changeset cs:7@br:/main@rep:default@repserver:TRISKELION:8084

Now launch the sync, please note I don't have to specify the type of remote scm anymore, and I don't have to type the svn url either because it gets "saved" after the first sync.

  $ cm sync main
    Last equivalence found 6 -> 6
    No new revisions to pull from the foreign SCM
    Changesets to push
    7 - 01/10/2011 8:06:19 - pablo - added bye.txt
    Check commit
    Committed changeset 7

Launch the sync again and it tells there are no changes to push or pull anymore.

   $ cm sync main
    Last equivalence found 7 -> 7
    No new revisions to pull from the foreign SCM
    Branches are in sync. There are no changesets to push or pull

Concurrent change scenario

Now, the guy at the plastic and the svn sides make changes concurrently, what will it happen? Let's go.

Add a new file in plastic:

   $ echo newest > newest.txt

   $ cm add newest.txt
    The selected items are about to be added. Please wait ...
    Item newest.txt was correctly added

   $ cm ci -c="added newest.txt on plastic"
    The selected items are about to be checked in. Please wait ...
    Assembling checkin data
    Validating checkin data
    Uploading file data
    Uploaded 9 bytes of 9 bytes (100%)
    Confirming checkin operation
    Modified c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk
    Added c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\newest.txt
    Created changeset cs:8@br:/main@rep:default@repserver:TRISKELION:8084

Now we modify a different file in SVN, ok?

I launch the sync again, read the details

   $ cm sync main
    Last equivalence found 7 -> 7
    Latest cset on foreign SCM: 8
    Changesets to pull
    8 - 01/10/2011 8:08:12 -  - =modified bye.txt on svn
    Changesets to push
    8 - 01/10/2011 8:08:24 - pablo - added newest.txt on plastic
    There are changesets to push and pull.
    Will pull the remote changes then you'll have to merge them and push the changes back.

What happened?

   $ cm find changeset
    10       0        /main                01/10/2011 08:04:35 all      default Root dir
    20       1        /main                01/10/2011 07:18:16 pablo    default trunk created
    4348     2        /main                01/10/2011 07:19:30 pablo    default initial code import
    4367     3        /main                01/10/2011 07:28:25 pablo    default hud.txt modified
    4379     4        /main                01/10/2011 07:30:28 pablo    default trunk created
    4384     5        /main                01/10/2011 08:00:04 pablo    default hello.txt added
    4388     6        /main                01/10/2011 08:03:00 pablo    default modified hello.txt
    4397     7        /main                01/10/2011 08:06:19 pablo    default added bye.txt
    4405     8        /main                01/10/2011 08:08:24 pablo    default added newest.txt on plastic
    4410     9        /main                01/10/2011 08:08:12 pablo    default =modified bye.txt on svn

    Total: 10

The "remote" changeset from SVN has been pulled but since there's a conflict, I'll have to merge before pushing back to svn.

   $ cm merge cs:9
    The file /bye.txt#br:/main#1 was modified on source and will replace the destination version

   $ cm merge cs:9 --merge
    The file /bye.txt#br:/main#1 was modified on source and will replace the destination version
    Merging c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\bye.txt
    The revision c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\bye.txt@9 has been loaded

   $ cm ci -c="merged from cs9 coming from svn"
    The selected items are about to be checked in. Please wait ...
    Assembling checkin data
    Validating checkin data
    Uploading file data
    Confirming checkin operation
    Modified c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk
    Copied c:\Users\pablo\wkspaces\testwkspaces\svnsync\plasticwk\bye.txt
    Created changeset cs:10@br:/main@rep:default@repserver:TRISKELION:8084

Now I run the sync again. Plastic is going to push the new cset (the merged cset) that will contain the changes between the merged cset (10) and the imported cset from svn (9) hence the changes introduced in 8.

   $ cm sync main --preview
    Last equivalence found 9 -> 8
    No new revisions to pull from the foreign SCM
    Changesets to push
    10 - 01/10/2011 8:09:58 - pablo - merged from cs9 coming from svn

   $ cm sync main
    Last equivalence found 9 -> 8
    No new revisions to pull from the foreign SCM
    Changesets to push
    10 - 01/10/2011 8:09:58 - pablo - merged from cs9 coming from svn
    Check commit
    Committed changeset 9

Now, how does it look like from the SVN side?

   $ svn diff -r 9:8
    Index: newest.txt
    ===================================================================
    --- newest.txt  (revision 9)
    +++ newest.txt  (revision 8)

The file "newest.txt" was added on changeset 8 in Plastic and is now in SVN! Great, isn't it? I expect to get it merged asap into the next 4.0 beta release.

Pablo Santos

I'm the CTO and Founder at Códice.
I've been leading Plastic SCM since 2005. My passion is helping teams work better through version control.
I had the opportunity to see teams from many different industries at work while I helped them improving their version control practices.
I really enjoy teaching (I've been a University professor for 6+ years) and sharing my experience in talks and articles.
And I love simple code. You can reach me at @psluaces.