<h1>Why Git?</h1> - Git is widely accepted by software developers owing to its usability and performance - Git has powerful branching capabilities. Developing new features on a new branch ensures that the master branch is not affected - Free Github and Gitlab services offer easy auditing of branches and code merges - Convenient interfaces for new code integration, peer reviews, and issue follow-ups - For students greater exposure to modern software development tools - Among other nuclear and particle physics experiments, STAR is probably the only active experiment that has not switched to Git. For example, see public software repositories of ALICE, ATLAS, CMS, DUNE, EIC, sPHENIX

<h1>Migrating from CVS to Git</h1> - Most of the machinery is ready and available - Use `cvs2git` utility to do a CVS to Git conversion of select CVS directories - Tools and documentation in support repository https://github.com/star-bnl/star-git-tools - The intention is not to convert the entire CVS repository but only the code used in reconstruction. E.g. the "user" and "STAR notes" directories are not part of the migration - No transition period is intended, i.e. do conversion once and set CVS^† to read only - In Git committers are identified by their email - The mapping between the RACF accounts and the user's name and email from the STAR collaborator database is available - Based on the positive experience of the BNL's NPP software group it is recommended to host the central copy of the new Git repository on Github. - Primary concerns are: Repository size and unfamiliar workflow

<h1>Skimming STAR Codebase</h1> <div style="font-size: 93%;"> - Skimming is performed in two steps. For details see [Backup Slides](#/excluded) - **Step 1:** Exclude select directories from conversion - **Step 2:** Remove individual files (large or unused blobs) - Main (small) inconvenience is that one cannot expect identical equivalence between Git and CVS tagged trees <table style="margin: -0.8em 0 0 -0.5em;"> <tr><td style="vertical-align: top;"> - Consider several skimming scenarios - R5 is most aggressive, R1 is the least - R5 excludes more files than R4, R4 excludes more files than R3, and so on - Notably, in R3 we exclude all external generators (Pythin{6,8}, HIJING, UrQMD, etc) present in CVS - Bare sizes under 200MB achievable - The recommended scenario is R4 <td style="width: 50%; vertical-align: bottom;"> <img class="plain" src="graphics/cvs2git.png" /> </table> </div>

<h1>Partial Clone, Sparse Checkout</h1> - Sparse checkout (i.e. checkout of specific subdirectories selected by the user) is available since early versions of Git and works reliably. UI improved in recent versions - Partial clone is a relatively new feature (documented in recent versions). UI does not appear very stable - We provide a simple interface to help CVS users with adoption of Git<br> https://github.com/star-bnl/star-git-tools <table> <tr> <td style="width: 60%;"> CVS like checkout <pre style="font-size: 0.85em;"><code data-trim class="shell"> $ git star-checkout StRoot/StMuDSTMaker StRoot/StPicoEvent Cloning into 'star-cvs'... $ tree -a -L 2 star-cvs/ star-cvs/ |-- .git | ... `-- StRoot |-- StMuDSTMaker `-- StPicoEvent </code></pre> <td> Manageable size <pre style="font-size: 0.85em;"><code data-trim class="shell"> $ du -b --si -d1 star-cvs/ 29M star-cvs/.git 1.3M star-cvs/StRoot 30M star-cvs/ </code></pre> </table>

<h1>Summary</h1> - Check out and look around: https://github.com/star-bnl/star-cvs - Currently synced with CVS but will be removed after final migration - Proposed name for the final repository is `star-sw`. Cf. `cms-sw`, `alisw` - Wait for production team to report any issues with building the code coming from the new source - Agree on a date when CVS^† will be set to read only mode - **Workflow** - Propose the usual workflow for the central repository:<br> Fork the repo → clone → make changes → push to your fork → create pull request - For the central repo it is suggested to have at least two designees to sign off before merging - A software coordinator and someone from the S&C management team? - This should encourage smaller set of changes - Users can share their forks for a quicker turn around - For more Git see multitude tutorials on the web

Backup Slides

<h1>Excluded Paths — Step 1</h1> <div style="width: 50%; float: left;"> R1: baseline scenario <pre style="width: 400px; font-size: 0.8em;"><code data-trim style="height: 200px;"> - /.backup - /Cons - /CVSROOT - /cgi - /conf - /Dsv - /group - /HISTORY - /obsolete - /offline - /online - /quaranteene.zip - /RealFiles.lis - /root - /root3 - /root5 - /scripts - /QtRoot </code></pre> R2: all of R1 and the following <pre style="width: 400px; font-size: 0.8em;"><code data-trim> - /StarDb/AgiGeometry - /StarDb/VmcGeometry </code></pre> R5: all of R4 and the following <pre style="width: 500px; font-size: 0.8em;"><code data-trim> - /StRoot/StJetMaker/StarTrigSimuSetup - /StRoot/StSpinPool/StMCAsymMaker </code></pre> </div> <div style="float: left;"> R3: all of R2 and the following <pre style="width: 500px; font-size: 0.8em;"><code data-trim style="height: 200px;"> - /StRoot/StarGenerator/Hijing1_383 - /StRoot/StarGenerator/Photos3_61 - /StRoot/StarGenerator/Pepsi - /StRoot/StarGenerator/Pythia6_2_22 - /StRoot/StarGenerator/Herwig6_5_20 - /StRoot/StarGenerator/Pythia6_4_23 - /StRoot/StarGenerator/Pythia6_4_28 - /StRoot/StarGenerator/HepMC2_06_09 - /StRoot/StarGenerator/EvtGen1_06_00 - /StRoot/StarGenerator/Tauola1_1_5 - /StRoot/StarGenerator/Pythia8_1_62 - /StRoot/StarGenerator/Pythia8_1_86 - /StRoot/StarGenerator/Pythia8_2_35 - /StRoot/StarGenerator/UrQMD3_3_1 </code></pre> R4: all of R3 and the following <pre style="width: 500px; font-size: 0.8em;"><code data-trim style="height: 300px;"> - /pams/gen/Herwig6_5_20 - /pams/gen/hijing_381 - /pams/gen/hijing_382 - /pams/gen/hijing - /pams/gen/Pythia6_2_05 - /pams/gen/Pythia6_2_20 - /pams/gen/Pythia6_4_22 - /pams/gen/Pythia6_4_23 - /pams/gen/Pythia6_4_26 - /pams/gen/Pythia6_4_28s - /pams/gen/pythia_6222 - /pams/gen/pythia_6410 - /pams/gen/pythia_6410t - /pams/gen/herwig </code></pre> </div>

<h1>Excluded Paths — Step 2</h1> - Files removed from the Git repository using the `bfg` utility program - Manually selected files: <pre style="width: 500px; font-size: 0.8em;"><code data-trim> StarDb/AgiGeometry/devE.h StarDb/AgiGeometry/devT.h StRoot/RTS/EventTracker/mapbin.h StarVMC/geant3/data/xsneut95.dat pams/sim/gphysdata/xsneut96.dat tpcPadGainT0B.*.root tpcDriftVelocity.*.C </code></pre> - Files larger than 200 kB and not present in any release/tag `SL1*` or `SL2*`