How do Centralized and Distributed Version Control Systems Impact Software Changes?
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The document analyzes how centralized (SVN) and distributed (Git) version control systems impact software changes based on a survey of 820 developers and analysis of 132 repositories. The key findings are: 1) Commits are typically smaller in Git (34% smaller) than SVN due to the ability to commit privately without merging. 2) Developers split changes more often in Git (81% vs 68% for SVN) due to easier commit processes and tools for splitting changes. 3) Developers prefer Git over SVN for its features like private commits, while some prefer SVN out of habit or ease of use.
![10
“Git promotes the idea that your commit space is
not inflicting pain on anybody else […] it
promotes small frequent commits […] rather
than the 5pm commit”
RQ1: Does the type of VCS
affect commit size?](https://image.slidesharecdn.com/slides-icse14-140606012734-phpapp02/85/How-do-Centralized-and-Distributed-Version-Control-Systems-Impact-Software-Changes-24-320.jpg)
![RQ2: Do developers split
their changes?
15
0%
25%
50%
75%
100%
SVN Git
6%6%
13%27%
81%
68%
Split their changes Group their changes
Other
“[changes] should be logically separated to
easily allow [the] commit message to drive [the]
review”](https://image.slidesharecdn.com/slides-icse14-140606012734-phpapp02/85/How-do-Centralized-and-Distributed-Version-Control-Systems-Impact-Software-Changes-33-320.jpg)
![16
0%
25%
50%
75%
100%
SVN Git
12%11%
6%5%
45%62%
37%
22%
By implementation By issue
Policy Other
RQ2: Do developers split
their changes?
“[Git] gives useful tools for splitting or merging
commits”](https://image.slidesharecdn.com/slides-icse14-140606012734-phpapp02/85/How-do-Centralized-and-Distributed-Version-Control-Systems-Impact-Software-Changes-35-320.jpg)
![18
RQ2: Do developers split
their changes?
For Git, more users (37%) split changes based
on implementation details that in SVN (22%).
“Each commit is one cohesive change […] (like
‘sphere class can now calculate its own volume’)
- user level features usually take many commits.”](https://image.slidesharecdn.com/slides-icse14-140606012734-phpapp02/85/How-do-Centralized-and-Distributed-Version-Control-Systems-Impact-Software-Changes-40-320.jpg)
![21
RQ3: Why do developers
prefer one VCS over another?
“You get to commit to a local repository and make
your changes public only when they are ready”
“I found the commit process very straightforward […]”](https://image.slidesharecdn.com/slides-icse14-140606012734-phpapp02/85/How-do-Centralized-and-Distributed-Version-Control-Systems-Impact-Software-Changes-51-320.jpg)
How do Centralized and Distributed Version Control Systems Impact Software Changes?
- 1. How Do Centralized and Distributed Version Control Systems Impact Software Changes? Caius Brindescu Mihai Codoban Sergii Shmarkatiuk Danny Dig 1
- 2. 2 GitHub is the main “forge” for OSS projects SourceForge 300K repos GitHub 4.6M repos
- 3. What’s the difference? 3 Git SVN History Local to every user On the server Commits Private, local Centralized, public Branching and merging Cheap Expensive History Modifiable “Set in stone”
- 4. What’s the difference? 3 Git SVN History Local to every user On the server Commits Private, local Centralized, public Branching and merging Cheap Expensive History Modifiable “Set in stone”
- 5. What’s the difference? 3 Git SVN History Local to every user On the server Commits Private, local Centralized, public Branching and merging Cheap Expensive History Modifiable “Set in stone”
- 6. What’s the difference? 3 Git SVN History Local to every user On the server Commits Private, local Centralized, public Branching and merging Cheap Expensive History Modifiable “Set in stone”
- 7. 4 What are we missing? Developers Managers Researchers Tool Builders
- 8. 4 What are we missing? Developers Managers Researchers Tool Builders
- 9. Are they using the tools to their full potential? 4 What are we missing? Developers Managers Researchers Tool Builders
- 10. Are they using the tools to their full potential? 4 What are we missing? Developers Managers Researchers Tool Builders
- 11. Are they using the tools to their full potential? 4 What are we missing? Is switching to Git good? Developers Managers Researchers Tool Builders
- 12. Are they using the tools to their full potential? 4 What are we missing? Is switching to Git good? Developers Managers Researchers Tool Builders
- 13. Are they using the tools to their full potential? 4 What are we missing? How does this new paradigm affect mining software repositories? Is switching to Git good? Developers Managers Researchers Tool Builders
- 14. Are they using the tools to their full potential? 4 What are we missing? How does this new paradigm affect mining software repositories? Is switching to Git good? Developers Managers Researchers Tool Builders
- 15. Are they using the tools to their full potential? 4 What are we missing? How does this new paradigm affect mining software repositories? Is switching to Git good? Are they building the right tools? Developers Managers Researchers Tool Builders
- 17. Survey 5 820 participants 85% from industry 56% have over 10 years experience 51% work in teams of 6 or larger
- 18. Repository Analysis 6 132 repositories 358K commits 409M LOC
- 19. Repository Analysis 6 358K commits 409M LOC 52 SVN 51 Git 29 Hybrid
- 20. Git is the most used VCS 7 0% 15% 30% 45% 60% 5%1% 9% 12% 20% 53% Git SVN Hg MS TFS CVS Other
- 21. We identified 3 themes 8 2. Impact of the team size on the VCS 3. Impact of the VCS on the software process RQ 6: Does team size affect the choice of VCS? RQ 7: Are larger teams more likely to use Issue Tracking Systems (ITS)? RQ 8: Does team size affect the size of commits? RQ 9: Does team size influence commit squashing? RQ 10: Does the type of VCS influence the presence and the number of issue tracking labels (ITL)? RQ 11: Is there a correlation between the number of ITLs in the commit message and the commit size? RQ 12: How does the size of commits vary in time? 1. Impact of VCS on developer’s behavior RQ 1: Does the type of VCS affect the size of commits? RQ 2: Do developers split their commits into logical units of change? How do they do it? RQ 3: How often and why do developers squash their commits? RQ 4: Why do developers prefer one Version Control System over another? RQ 5: Does the VCS influence the frequency with which developers commit?
- 22. We identified 3 themes 8 2. Impact of the team size on the VCS 3. Impact of the VCS on the software process RQ 6: Does team size affect the choice of VCS? RQ 7: Are larger teams more likely to use Issue Tracking Systems (ITS)? RQ 8: Does team size aff RQ 9: Does team size influence commit squashing? RQ 10: Does the type of VCS influence the presence and the number of issue tracking labels (ITL)? RQ 11: Is there a correlation between the number of ITLs RQ 12: How does the size of commits vary in time? 1. Impact of VCS on developer’s behavior RQ 1: Does the type of VCS affect the size of commits? RQ 2: Do developers split their commits into logical units of change? How do they do it? RQ 3: How often and why do developers squash their commits? RQ 4: Why do developers prefer one Version Control System over another? RQ 5: Does the VCS influence the frequency with which developers commit?
- 23. RQ1: Does the type of VCS affect commit size? For Git and SVN the difference was statistically significant 9 LOC 0 10.5 21 31.5 42 Mean 23.20 40.06 SVN Git
- 24. 10 “Git promotes the idea that your commit space is not inflicting pain on anybody else […] it promotes small frequent commits […] rather than the 5pm commit” RQ1: Does the type of VCS affect commit size?
- 25. For repositories that transitioned, there was no statistically significant difference 11 RQ1: Does the type of VCS affect commit size? LOC 0 6.5 13 19.5 26 Mean 25.72 23.02 Hybrid-SVN Hybrid-Git
- 26. 12 Git repositories have commits size 34% smaller than SVN repositories, in terms of LOC RQ1: Does the type of VCS affect commit size?
- 27. 12 Git repositories have commits size 34% smaller than SVN repositories, in terms of LOC One possible explanation is that each developer commits to their own local repo, with no need for synchronization or merging their changes. Hybrid repos keep the same commit size because of existing policies. RQ1: Does the type of VCS affect commit size?
- 28. 12 Git repositories have commits size 34% smaller than SVN repositories, in terms of LOC One possible explanation is that each developer commits to their own local repo, with no need for synchronization or merging their changes. Hybrid repos keep the same commit size because of existing policies. RQ1: Does the type of VCS affect commit size? Old habits die hard
- 29. Implications Smaller commits makes it easier to “bisect” the tree Git offers better tools for splitting commits Some repositories migrate from one paradigm to the other; this might bias the results Changing the VCS is not enough 13
- 30. Separating the changes to the working copy into multiple, separate commits 14 RQ2: Do developers split their changes? file1.txt file2.txt! file3.txt file1.txt file2.txt! file3.txt
- 31. Separating the changes to the working copy into multiple, separate commits 14 RQ2: Do developers split their changes? file1.txt file2.txt! file3.txt Commit 1 Commit 2
- 32. RQ2: Do developers split their changes? 15 0% 25% 50% 75% 100% SVN Git 6%6% 13%27% 81% 68% Split their changes Group their changes Other
- 33. RQ2: Do developers split their changes? 15 0% 25% 50% 75% 100% SVN Git 6%6% 13%27% 81% 68% Split their changes Group their changes Other “[changes] should be logically separated to easily allow [the] commit message to drive [the] review”
- 34. 16 0% 25% 50% 75% 100% SVN Git 12%11% 6%5% 45%62% 37% 22% By implementation By issue Policy Other RQ2: Do developers split their changes?
- 35. 16 0% 25% 50% 75% 100% SVN Git 12%11% 6%5% 45%62% 37% 22% By implementation By issue Policy Other RQ2: Do developers split their changes? “[Git] gives useful tools for splitting or merging commits”
- 36. 76% of developers split their commits. The percentage is higher for Git (81.25%), compared to SVN (67.89%). 17 RQ2: Do developers split their changes?
- 37. 76% of developers split their commits. The percentage is higher for Git (81.25%), compared to SVN (67.89%). 17 RQ2: Do developers split their changes? We attribute this to an easier commit process.
- 38. 76% of developers split their commits. The percentage is higher for Git (81.25%), compared to SVN (67.89%). 17 RQ2: Do developers split their changes? We attribute this to an easier commit process. Overall, developers choose to split their commits based on the issue they belong to.
- 39. 18 RQ2: Do developers split their changes? For Git, more users (37%) split changes based on implementation details that in SVN (22%).
- 40. 18 RQ2: Do developers split their changes? For Git, more users (37%) split changes based on implementation details that in SVN (22%). “Each commit is one cohesive change […] (like ‘sphere class can now calculate its own volume’) - user level features usually take many commits.”
- 41. Implications Doing this makes it easier to perform other operations such as cherry-picking. 19
- 42. Implications Doing this makes it easier to perform other operations such as cherry-picking. 19 For mining software repositories, Git might be better since it allows smaller atomic changes. Splitting changes is a manual and tedious process. Tool builders could make their tools support this process
- 43. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 44. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 45. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 46. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 47. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 48. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 49. RQ3: Why do developers prefer one VCS over another? 20 0 12.5 25 37.5 50 Killer features Old habit Ease of use Personal pref. Other 9% 2% 20% 23% 46% 5%1% 42%42% 11% SVN Git
- 50. 21 RQ3: Why do developers prefer one VCS over another? “You get to commit to a local repository and make your changes public only when they are ready”
- 51. 21 RQ3: Why do developers prefer one VCS over another? “You get to commit to a local repository and make your changes public only when they are ready” “I found the commit process very straightforward […]”
- 52. 22 RQ3: Why do developers prefer one VCS over another? Git is preferred because of its “killer features” SVN is preferred because of it’s easier to use and because of familiarity
- 53. Implications 23 Tool builders should focus on features that complement the developer’s workflow. While Git has a steep learning curve, it does allow for better ways to manage your changes.
- 54. RQ4: Do developers squash their commits 24 What is squashing?
- 55. 25 RQ4: Do developers squash their commits 0% 15% 30% 45% 60% Git 8.62 55% 37% Yes No N/A
- 56. Why do they do it? Developers using Git mention two different reasons (a) grouping several changes together (b) they only care about the final solution, not the path they took to get there 26 RQ4: Do developers squash their commits
- 57. 27 RQ4: Do developers squash their commits Over 1/3 of developers squash their commits Large teams squash commits more often then small ones
- 58. Implications 28 Tool builder could allow for non-destructive history modifications, e.g.: hierarchical commits Git allows users to change history before they make it public or available to others.
- 59. Threats Squashing Age bias OSS vs. Proprietary software 29
- 60. Conclusions 30 The commit size is smaller in Git than SVN. Developers split their changes more often in Git, using a finer granularity. 1/3 of developers use squashing to change the history. cope.eecs.oregonstate.edu/VCStudy Teams of all sizes predominantly prefer Git (71%)