comparação - perforce x subversion
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Comparison: Perforce and Subversion
Perforce 2011.1 and Subversion 1.7 This document compares Perforce (version 2011.1) with Subversion (version 1.7). Read this compari-son to:
•UnderstandPerforceandSubversion’smajorfeaturedifferences
•Seehead-to-headmetricsforoperationslikebranching,merging,check-ins,andcheckouts
•Getageneralcomparisonoftheeffectsofscalingonbothsystems
Comparison: Perforce and Subversion
Table of ContentsExecutive Summary _______________________________________________________________ 1
Overview ________________________________________________________________________ 1
Branching, Merging, and Release Management ______________________________________ 2Subversion ________________________________________________________________ 2Basic Branching and Merging _______________________________________________ 2Branching Model, Dependencies, and Guidance _______________________________ 3
Perforce _____________________________________________________________________ 3Basic Branching and Merging _______________________________________________ 3Branching Model, Dependencies, and Guidance _______________________________ 4
Workspaces and Collaboration _____________________________________________________ 5Subversion ___________________________________________________________________ 5Perforce _____________________________________________________________________ 5
Visual Tools ______________________________________________________________________ 5Subversion ___________________________________________________________________ 5Perforce _____________________________________________________________________ 5
Defect Tracking __________________________________________________________________ 6Subversion ___________________________________________________________________ 6Perforce _____________________________________________________________________ 6
Integration with Related Tools _____________________________________________________ 6Subversion ___________________________________________________________________ 6Perforce _____________________________________________________________________ 6
Remote Development _____________________________________________________________ 7Subversion ___________________________________________________________________ 7Perforce _____________________________________________________________________ 7
Scalability and Performance _______________________________________________________ 8Subversion ___________________________________________________________________ 8Perforce _____________________________________________________________________ 8
Digital Asset Management and Storage _____________________________________________ 8Subversion ___________________________________________________________________ 8Perforce _____________________________________________________________________ 8
Support and Maintenance _________________________________________________________ 9Subversion ___________________________________________________________________ 9Perforce _____________________________________________________________________ 9
Administration and Security _______________________________________________________ 9Subversion ___________________________________________________________________ 9Perforce _____________________________________________________________________ 9
Auditing, Compliance, and Reporting ____________________________________________________________________ 9
Subversion ___________________________________________________________________ 9Perforce _____________________________________________________________________ 9
Benchmarks _____________________________________________________________________ 10Test Platform ________________________________________________________________ 10Test Data____________________________________________________________________ 10Test Results _________________________________________________________________ 10
Appendix A: Detailed Branching and Merging Analysis ______________________________ 12Results Summary _____________________________________________________________ 12Intended Workflow ___________________________________________________________ 12Subversion’s Problems with Base Selection and Merge History _____________________ 12
1 Comparison: Perforce and Subversion
EXECUTIVE SUMMARYThechoiceofsoftwareversionmanagementsystemhasaprofoundimpactonthoseinvolvedindigitalassetmanagement,fromsoftwaredeveloperstoartiststomanagers.Aneffectivesoftwareversionmanagementsystemisonethat:
• Providesafullhistoryoftheevolutionofdigitalassets
• Enablesparalleldevelopmentandconcurrentteamactivity
• Helpstheentireteamworkmoreefficiently
• Meetsmoderndevelopmentandscalabilitychallenges
• Isfast,flexible,andreliable
ThisdocumentshowsthatPerforceSoftwareVersionManagementhasmaintaineditscorestrengthsinproductivity,collaboration,branchingandmerging,scalability,andadministration,whileofferinginnovativesolutionsfornewsoftwareversionmanagementchallenges.Subversion,ontheotherhand,hasfocuseditseffortsonaddressingshortcomingsinbasicfunctionality.Althoughthetotalcostofownershiporreturnoninvestmentisoutsidethescopeofthisdocument,itbecomesclearthatPerforceisthestrongersolutionformodernsoftwareversionmanagement.
Attribute Subversion Perforce
Branching, Merging, and Release Management
Subversionoffersbranching,andprovidesbasicmergehistorytrackinginthedestinationfile’sattributes.Subversion’smergealgorithmsdonotoperatewellinallscenarios.Branchingframeworkandreleasemodelaredesignatedbyconvention,withrepository-widehooksavailableforguidance.Dependenciesaremanagedwithexternals.
Perforceautomaticallytracksthehistoryofallbranchoperationswithitsadvancedandmaturemergetrackingmechanisms.Streamsprovidebest-practicesbranchingframework.Granulartriggersandbrokerareavailableforguidance.Dependenciesaremanagedviaflexiblestream,branch,andworkspaceviews,orviaremotedepot.
Workspaces and Collaboration Importantmetadatastoredintheworkspaceonly;corruptionoftheworkspaceisdifficulttorecoverfrom.Noshelvingfacility.Changelistsareaclient-onlyconcept;nowaytoseewhatothersareworkingonorpreventconcurrenteditingoffilesthatcannotbemerged.
Workspacedefinitionstoredonthesharedversioningserviceandcanberecreated.Shelvingofferssimpletaskswitching,taskhandoff,andcodereview.Changelistsaretrackedonthesharedversioningservice.Theopen-edit-submitworkflowprovidestransparencyintocurrentworkandalsohelpspreventconcurrentworkonfilesthatcannotbemerged.
Visual Tools Communitysupportedtoolsavailable;usuallyspecifictoasingleplatformorenvironment.
Fullfeaturedmultiplatformvisualapplication.VisualizationtoolsincludeStreamGraphandMergeQuest.
Defect Tracking NotincludedwithSubversion;usersneedtouseaseparatedefecttrackingsolution.
Perforceprovidesabasicdefecttrackingsystemcalledjobs,andintegrateswithleadingthird-partydefecttrackingsystemssuchasHPQualityCenterandAtlassianJIRA.
Integration with Related Tools Integrationsareavailableviatheopensourcecommunity.
PerforceintegrateswithleadingIDEs,suchasEclipseandVisualStudio,andothertoolsinmanycategories.IntegrationtoolsincludetheDefectTrackingGatewayandseveralfullysupportedAPIs.
OVERVIEW
2 Comparison: Perforce and Subversion
BRANCHING, MERGING, AND RELEASE MANAGEMENT
Subversion
Basic Branching and MergingSubversionofferscodelinebranchingusingasimplecopycommandtocreateabranch,andkeepsabasichistoryoftheoperationsattachedtoeachfileindividuallyinfile-keyedattributelists.Subversionmergesareslowandhistoricallyhave
beenproblematicandpronetomergeerrors.Bidirectionalanddivergentmergesaresupportedwithnewerserversandclients,butwithextramergestepsinvolved.1Othercomplexmergingcases,particularlyinvolvingrenamesandtreeconflicts,canbedifficulttoresolve.2Mergingrenamedfilesmayoverwritenewerrevisionsonthetargetbranchorcauseatreeconflict.3
1Forexample,afterpromotingafeaturebranchintothetrunkwithareintegratemerge,thefeaturebranch
cannotbeusedunlessthetrunkismergedinandthatchangeignored.Subversiondoesnotproperlytrack
mergehistoryinthesecases.
2Subversiontreatsarenameasacombinationofacopyanddelete.
3http://svnbook.red-bean.com/en/1.6/svn.branchmerge.advanced.html#svn.branchmerge.advanced.moves
Overview(continued)
Attribute Subversion Perforce
Remote Development Remoteslaveserverscanbesynchronizedfromacentralizedmasterserver.Synchronizationmechanismrequiresthecodingofevent-basedscripts.
P4Sandboxoffersconnectionindependentversioningandprivatelocalbranching.ThePerforceProxyServiceoffersafilecachingsolutionforremoteusers,withminimaladministrativeoverhead.ReplicationServicesprovideafullcopyof“thesharedversioningservices”dataatremotelocationsforread-onlyoperations.
Scalability and Performance SubversiondependsheavilyonCPU-intensiveoperationsthatdonotscalewellwhenworkloadsincrease.SubversionusuallyrunsasanApachemodule.PerformancebenchmarksindicatethatSubversiondoesnotscalewellindemandingenvironments.
Perforce’sarchitectureisprovenandcontinuestoscalewelluptoandbeyondmanyterabytesandtensofmillionsofversionedfiles.Architectedforspeed,Perforcescaleslinearlyandiscurrentlydeployedinenvironmentswith10,000+usersandheavyautomation.Proxy,Broker,replicationservices,andP4Sandboxprovideapowerfulandflexibledeploymentarchitecture.Perforcesupportsaggressivecontinuousintegrationandautomationwithnoimpactonthesharedversioningservice.
Digital Asset Management and Storage
Inefficientatstoringlargedigital(binary)assets.Sharedstorageformetadataandversionedfiles.
Effectivelystoresanykindofdigitalasset.Storageformetadataisseparatefromversionedfilestorage,whichcanusedifferentstoragesystemsfordifferentproductsorfiletypes.
Support and Maintenance Availableatadditionalcostfromthirdparties.Olderreleasesunsupportedaftertwomajorincrements.
World-classtechnicalsupport,training,andprofessionalservicesprovidedbyPerforce.Productssupportedforalongtimewithadefinedsunsettingpolicy.
Administration and Security Severaldeploymentoptionsavailable,oftenrequiringanApachewebserver.Securityoftendoneattherepositoryordirectorylevel.Inconsistenttoolsacrossplatforms.Upgradesoftenmustbedonesimultaneouslyforserverandclient,andsometimesrequiremakingnewworkspaces.
Simple,consistentdeployment.Granularaccesscontrol.Excellentcross-platformsupport.Simpleupgradeprocedureswithgoodinteroperabilityacrossversions.
Auditing, Compliance, and Reporting
UtilizesApacheloggingforauditing.Reportingdoneviacommand-linescripts.
Built-inauditlog.Reportingcanbedoneviacommandline,scriptingAPIs,customSQLqueries,orareportengine.
3 Comparison: Perforce and Subversion
STEP 2
STEP 1 STEP 3
STEP 5
STEP 4 STEP 6
STEP 7
1:1 ----2:2 ----
Rev 1
DEV
MAIN
1:1 ----2: foo2 ----
Rev 2
1:1 ----2: bar2 ----
Rev 3
1:1 ----2:2 ----
Rev 1
1: edit1 ----2:2 ----
Rev 2
1: edit1 ----2: foo2 ----
Rev 3
1: edit1 ---<<<<<< .working2: bar======2: foo>>>>>> .merge-right2: ----
Rev 4
CONFLICT
Figure 1: A simple merge scenario in which Subversion causes a merge conflict.
AsonesimpleexampleofacasewhereSubversionmergingdoesnotworkproperly,considerthefollowingscenarioillustratedinFigure1.
Inthisscenario,afilewasbranchedimmediatelyaftercreation,severaleditsweremadeonbothbranches,andsomeofthechangesfromthechildbranchweremergedback.InStep7,wetrytomergethelatestchangesfromtheparenttothechild.Subversionselectsthefirstparentrevisionasthemergebase,whichleadstoanunnecessarymergeconflict.
Thisscenario,andadetailedbranchingandmerginganalysisinAppendixA,showthatSubversioncannothandlemorecomplexmergescenarioswell,andofferslessgranularresolutioninmanysituations.
Branching Model, Dependencies, and GuidanceDevelopmentandreleasemanagementmodelsarebuiltbyconvention,usuallyusingaknowndirectorystructurefordifferentbranchtypes.Hookscanbeusedtoguidethesemodels,althoughSubversionhooksaffecttheentirerepositoryandmustbecodedappropriately.
DependenciesbetweenmodulesorprojectscanbemanagedusingSubversionexternals,whichrequirecarefulconfigurationandusage,andaredisjointinsomesensefromtherestofthe
workspace.ManySubversionoperations,forexample,willnotautomaticallyrecurseintoexternaldirectories.
Multipleproductscanbehousedinasinglerepositoryifthedirectorystructureisplannedinadvance,inwhichcaseserverstorageissharedamongsttheproducts.Alternatively,eachproductcanuseitsownindependentrepositoryandfilestorage,butatthecostofcommunicationandcodesharingbetweenproducts.
Perforce
Basic Branching and MergingThePerforceInter-FileBranchingmodelispowerfulandflexible,capableofbranchingthousandsoffilesrapidlywhileretainingacompletebranchandmergehistory(includingthemethodofresolvingmerges).Insteadofmanuallytrackingallchangesacrossbranches,userscanrelyuponPerforcetomergefilechangesacrossmultiplebranchesautomaticallyandwithfewerconflictstoresolve.Thisenablesavarietyofdevelopmentscenarios,suchascustomer-specificversions,experimentalbranches,personalortaskbranches,andtheclassicreleasebranchingpatterns.Abuilt-ingraphicaltool,RevisionGraph,canbeusedtodisplaythedetailedbranchinghistoryofeachfileforeasyvisualizationofcodepropagation(seeFigure2).
4 Comparison: Perforce and Subversion
Perforceinherentlyunderstandstheancestralrelationshipthatfilessharebetweenbranches.Onceachangehasbeenintegratedfromanoriginatingbranchintoatargetbranch,thereisnoambiguitythatthechangeexistsinbothbranches.Therefore,onsubsequentintegrationsfromthetargetbacktotheoriginatingbranch,userswillonlybepromptedtointegratechangesthathaveoccurreddirectlyinthetargetbranch.Thiskindofintegrationpatternisreferredtoasbidirectionalorladdermerging.
Perforce’smergeengineprovidesbothrobustnessandflexibility.Themostcomplexmergescenariosaresupported,includingrefactoring,indirectmerges,andhandlingnon-contentchanges.AdetailedbranchingandmerginganalysisisprovidedinAppendixA.
InthesimplemergescenariodescribedinFigure1,Perforcecorrectlyselectsthemergebaseonthetargetbranch,givingacleanmergewithnoconflicts(seeFigure3).
Branching Model, Dependencies, and GuidancePerforceStreamsprovidealightweightbutpowerfulbranchingmodel.Usingstreams,aproductarchitectcandefinetherelationshipbetweenstreams,andbetweenthemodulesthatcomposeaproduct;thearchitectcanalsodirecttheflowofchange(merges)betweenstreams.Thisinformationisusedtosimplifyandautomatemanyroutineoperationsforusers.
Whenusingeitherstreamsorregularbranching,Perforceoffersseveraltoolstoguideandenforcepolicy.Triggersandaccesscontrolaregranular,whilethePerforceBrokerprovidescommandfiltering.
Dependenciesbetweenmodulesorprojectsaremanagedviaflexiblestream,branch,orworkspaceviews.Alogicalworkingviewofaproductcanthusbeeasilyassembledfromseveralcomponentsdevelopedindependently.Remotedepotssupportcodedropsbetweenindependentrepositories.
Multipleproductscanbehousedinasingledepotoreachinitsowndepot,dependingonaccesscontrolandusagepolicies.Housingproductsinmultipledepotsallowsfordistributionofphysicalfilestorageontheversioningservice,animportantconsiderationforprojectswithlargedatavolumes.Theuseofmultipledepotsiseffectivelytransparenttotheenduser.
Figure 2: Perforce Revision Graph
STEP 2
STEP 1 STEP 3
STEP 5
STEP 4 STEP 6
STEP 7
1:1 ----2:2 ----
Rev 1
DEV
MAIN
1:1 ----2: foo2 ----
Rev 2
1:1 ----2: bar2 ----
Rev 3
1:1 ----2:2 ----
Rev 1
1: edit1 ----2:2 ----
Rev 2
1: edit1 ----2: foo2 ----
Rev 3
Rev 4
1: edit1 ----2: bar2 ----
Figure 3: Perforce selects the correct merge base
5 Comparison: Perforce and Subversion
WORKSPACES AND COLLABORATION
SubversionSubversionstoresimportantmetadataandstateinformationintheworkspace.Recoveryfromworkspacecorruptionisoftendifficult,andrequirescreatinganewworkspace.PriortoSubversion1.7,eachdirectoryintheworkspacehada.svnfolder;accidentallydeletingasubdirectoryintheworkspacewouldresultinthatsubdirectorybeingunknowntotheworkspace,evenwhiletheparentdirectorywasintact.InSubversion1.7allmetadataisstoredintherootoftheworkspace,butthenewmetadatastorageformatissusceptibletocorruptionfromconcurrentaccess.
Subversionoffersnoshelvingfacility;storingandsharingworkinprogressrequiresusingabranch.
Subversion’schangelistsareclient-onlyconcepts.ThereisnowayinSubversiontoknowwhatothersareworkingonorpreventconcurrentcheckoutsoffilesthataredifficulttomerge,asSubversiondoesnotofferanopen-edit-submitworkflow.4
Subversionworkspacesusuallyofferasimple,monolithicviewoftherepositorystartingatthepointofcheckout.Sparsecheckoutsallowpruningorinclusionofsomepartsoftherepository,butcouldrequiremanystepsinordertoassemblethepropersetofdataintheworkspace.
4Subversiondoesofferad-hocfilelocking,whichrequiresthelockingusertoissueaspecialcommand.This
lockpreventsotherusersfromcommittingthelockedfile,butdoesnotpreventthemfromworkingonitin
thefirstplaceunlessaspecialfilepropertyisset.
Perforce AllimportantmetadatainPerforceisstoredonthesharedversioningservice.Recreatingalostworkspace(apartfromactualunsavedfilecontent)issimple.
Perforceshelvesprovideasimplewaytostoreworkinprogress,switchtasks,andshareworkinprogressforcodereview.
Perforcechangelistsareservice-sidemetadata,allowingalluserstoseewhatfilesarecheckedout.Perforcecanalsopreventconcurrentcheckoutsoffilesthataredifficulttomerge,whichhelpspreventwastedtimeandeffort.Perforcesupportsbothanopen-edit-submitworkflowandanedit-open-submitworkflow.
Perforceworkspaceviewsprovidealayerofabstractionbetweentheservice’sviewofthedataandtheviewonaworkstation.Usingaworkspaceview,ausercanpickandchoosedifferentpiecesofasharedrepositorytoview.Theviewiscapturedandversionedasimportantmetadata.
VISUAL TOOLS
SubversionCommunitysuppliedtoolsareavailableformostplatforms,buttheretendstobeadistinctionbetweenWindowsandotherplatforms.
Perforce Consistentvisualtoolsareavailableforallmajorplatforms.InnovativevisualizationslikeStreamGraph,Time-LapseView,MergeQuest,andHTML5applets,greatlyenhanceuserproductivity(seeFigures4-6).
dev2.3
rel2.1 rel2.2 rel2.3
main
Figure 4: Perforce Stream Graph
6 Comparison: Perforce and Subversion
DEFECT TRACKING
SubversionSubversiondoesnotincludedefecttracking,butalimitednumberofthird-partyintegrationsareavailable.Defecttrackingintegrationtypicallyreliesonfragilecommitmessageparsing.
PerforcePerforceprovidesabasicdefecttrackingsystemcalledjobs.Ajobtypicallyrepresentsanenhancementrequestorabugtobefixed.Jobdefinitionsarecustomizabletosupportmanyworkflows.Jobscanalsoworkwithseveralthird-partydefecttrackingsystems,suchasHPQualityCenterandAtlassianJIRA.DataenteredintoaPerforcejobisautomaticallyreplicatedinthedefecttrackingtool,andviceversa.Perforcecantellyouwhetherornotabugfixispresentinanyparticularcodeline,regardlessofthecodelineinwhichthebugfixoriginated.
UsingPerforcejobs,userscaneasilylinksubmittedchangestodefectrecordswithoutrelyingoncommitmessages.
INTEGRATION WITH RELATED TOOLS
SubversionTheopensourcecommunitysupportsdifferentSubversionGUIs,aswellasplug-insforworkingwithinpopularIDEs.
PerforcePerforcehasamaturemultiplatformGUI,andthereareplug-insformostofthepopularIDEs.IntegrationtoolsincludethePerforceDefectTrackingGatewayandseveralfully-supportedAPIs.Perforcealsohasintegrationsforpopularapplicationsincluding:
• IDEs
• Webandgraphicaltools
• Softwarebuildtools
• MicrosoftOffice
• Mergeanddifftools
Figure 5: Perforce Time Lapse View
main
dev-1.0dev-2.0
R1.0
0
0
0
0 1+
Figure 6: Perforce Merge Quest
7 Comparison: Perforce and Subversion
REMOTE DEVELOPMENT
SubversionWithSubversion,remotedevelopersworkdirectlyagainstlocalslaveservers.Allslavesareconfiguredtosynchronizetheirdatastoresfromacentralizedmaster.Event-basedscriptstriggeredbyupdatesinthemasternotifyeachregisteredremoteslavetosynchronizeitsarchive.Scriptsneedtobecreatedandthendeployedtobothslaveandmasterservers.Eachslaveservermustbeconfiguredtoeitherdenyallwriteaccessorproxywriterequeststhroughtothemasterserver.Iflocalcommitsaredonedirectlyonaslaveserver,thereisnoeasycorrection.
Switchingworkspacesbetweenmasterandslaveserversrequiresthateachuserrunaspecialcommand,makingitdifficulttoautomate.
Third-partycommercialtoolsarenecessarytoachieveadditionallevelsofperformanceatremotelocationsatanadditionalcost.
Perforce RemotedevelopmentwithPerforcedoesnotrequireanyadditionalprocessoverheadoradditionalcost.SeveraltoolssupportremotedevelopmentwithPerforceandaretypicallytransparenttotheenduser.
P4Sandboxsupportsconnectionindependentversioning,privatelocalbranching,andfastlocaloperations,inadditiontoitsotherworkflowbenefits.
PerforceproxiesatremotelocationssupportPerforce’sremotearchitecture(seeFigure7).ThePerforceProxycachesandservesfilestousersatremotelocations,therebyreducingtrafficacrossslowerWANlinks.Allusers,localorremote,connecttothesamesharedrepository,andlookatthesameprojectfiles.ThePerforceProxyrequiresminimaladministrativeattention.
PerforceReplicationServicesprovidecompletelylocalread-onlyoperationsforremoteusers.AsalargepercentageofPerforceoperationsareread-only,usingalocalReplicationServiceoffersasignificantperformancebenefit.
Shared Versioning Service
Proxy Service
ReplicationService
P4Sandbox P4Sandbox
Figure 7: Perforce’s built-in distribution
8 Comparison: Perforce and Subversion
SCALABILITY AND PERFORMANCE
SubversionWithSubversion,thebinarydeltadifferencingschemeusedtoversionbothbinaryandtextfilesconsumesalargeamountofCPUtimeontheclientandserver.Thisisespeciallyproblematicwhenthefilesarelargeandtherearemanyconcurrentuserscompetingforthesameresources.PerforceeasilyoutperformsSubversioninallequivalentversioningoperationsduringcomparativebenchmarkingtests.
Onaqualitativenote,somevisualtoolsprovidedbypopularSubversionGUIscantakeanexcessivelylongtimetopresentinformation.Onarepositorywith13,000revisions,forinstance,theTortoiseSVNrevisiongraphtakesoverthreeminutestoloadarevisiongraphforasinglefilewithonlythreerevisions.
PerforcePerforceisarchitectedfirstandforemostforspeed.ThereversedeltaRCSformatfortextandGZipcompressiononbinaryfilesmeansusersdonotwaitforcheck-insandotherstandardoperations.Perforcescaleslinearly,sothereisnoperformancepenaltyimposedbythenumberofrevisionsorthesizeofanygivenfile(s).ThePerforceVerioningServicehasbeendeployedsuccessfullyinenvironmentswithseveralthousandusers,terabytesofversionedcontent,andmillionsofrevisions.Perforce’sdeploymentarchitecturenowincludesproxies,brokers,replicas,andP4Sandbox;thesetoolscanbedeployedinmanycombinationstosatisfydemandingenvironments.ReplicationServicesareparticularlyusefulforsupportingautomatedprocessessuchasaggressivecontinuousintegration;theperformanceburdenofsuchprocessesisshiftedentirelyawayfromtheproductionserver.
DIGITAL ASSET MANAGEMENT AND STORAGEAmodernversionmanagementsystemmustbeabletoeffectivelystoreandmanageanykindofdigitalasset,fromsourcecodetographicstochipdesigns.Otherwiseasecondsystemwillbenecessaryforstoringthesenon-textassets,whichrequiresextraoverhead,administration,andprocess.
Subversion Subversioncannoteffectivelystoreandmanagelargedigitalassets.ItsbinarydifferencingalgorithmimposesasevereCPUburdenontheclientworkstation,withunacceptableperformancedegradation.Additionally,aSubversionworkspacemaintainsapristinecopyofallfilecontentinadditiontotheactualworkingcopies.Withlargedatavolumes,thiscouldimposeaburdenonthetypicalworkstation.
Ontheserver,storageforasinglerepositoryisonasinglefilesystemforthemetadataandallversionedfiles,givingtheadministratorslittleflexibilitytodealwithlargedatavolumes.Subversionslaveserverscanbeusedtooffloadfiletransferwork,butswitchingworkspacesfromthemasterservertotheslaverequiresamanualstepbyeachuser.
PerforcePerforceisusedbycustomerstostoreandmanageterabytesofdigitalassetsofalltypes.Perforce’sefficientworkspacemanagementimposeslittleoverheadonclients.Onthesharedversioningservice,storagecanbepartitionedbetweenthemetadataandseveraldepotsforversionedfiles,givingadministratorsgreatflexibilityinplanningstoragesolutions.Ifmoregranularityisnecessary,particularfiletypescanbemanagedinseparatestorage,andunnecessarydatacanbearchivedtoofflinestorage.Perforcealsooffersseveraleasy-to-deploytoolsthataretransparenttobothendusersandtheprocessforoffloadingfiletransferworkfromtheprimaryservertosupportcontinuousbuilds,automation,andremoteusers.
9 Comparison: Perforce and Subversion
SUPPORT AND MAINTENANCE
SubversionSubversionoffersfullaccessibilitytothesourcecode,buttheadministratormustinvestthetimeandefforttobecomefamiliarwiththecodebase.Commercialthird-partysupport,training,andservicesarealsoavailable.Subversionstopssupportingolderreleasesaftertwomajorincrements.Forinstance,whenSubversion1.6wasreleased,supportforSubversion1.4wasdiscontinued.
PerforceExpertandresponsivetechnicalsupportisahallmarkofPerforceandfulltechnicalsupportisincludedduringanevaluation.Perforcebelievesthatwhenyoubuyasoftwareversionmanagementsystem,youarenotonlyputtingyourfaithinthesoftware,butalsointhetechnicalsupportyouexpecttoreceive.Becausethequalityofatechnicalsupportorganizationisbetterexperiencedthandescribed,Perforceencouragesprospectivecustomerstojudgeforthemselvesduringatypical45-daytrialevaluation.Perforcealsooffersafullrangeoftrainingandprofessionalservices.Perforceprovidestechnicalsupportforpastreleasesforanextendedduration,andhasadefinedpolicythatprovides12months’minimumnoticebeforeanolderproductisretired.
ADMINISTRATION AND SECURITY
Subversion Subversionrequiresadministratorstomakeseveraldecisionsbeforeimplementation.Forexample,administratorsmustdecidewhethertoconfigureawebserveroruseastandaloneSubversionserver;whichauthenticationandaccesscontrolmechanismstouse;andwhethertouseafile-basedsystemoradatabaseforstoringversionedfiles.Subversionaccesscontrolisnotgranular,andisoftendoneattherepositorylevel,althoughdirectory-levelaccesscontrolispossible.
Subversionimposesextraadministrativeoverhead.Itstoolsetisinconsistentacrossplatforms,forcingusersinmulti-platformenvironmentstoadaptaccordingly.Moreimportantly,theSubversionserverandclientsoftwaremustbeupgradedsimultaneouslyandoften,withmanualupgradestepsrequiredforclients.Insomecases,Subversionrecommendsmakingnewworkspacesratherthanupgradingexistingones.
Perforce Perforcefunctionsthesameregardlessofplatform,andprovidesabuilt-insecuritymechanismwithmanylevelsofaccessthatcanbeappliedtoanysubsetofthearchivedfiles—fromtheentiresharedrepositorytotheindividualfile.Versionedfilesarestoredthesameonallplatforms.
Perforceimposesminimaladministrativeoverhead.Perforcedeploymentissimpleandconsistent.Workinginamultiplatformenvironmentposesnoproblem,andPerforcehasexcellentsupportformixedserviceandapplicationversions.Upgradeproceduresaresimpleandfast.
AUDITING, COMPLIANCE, AND REPORTING
Subversion SubversionreliesonApachefacilitiesforauditlogging.ReportingismostoftendoneusingtheSubversioncommand-lineclient.
Perforce Perforcehasabuilt-inauditlog.ReportingispossibleviathePerforcecommandline,scriptingAPIs,SQLqueries,orreportengines.Thelattertwooptionsmakesophisticateddataminingpossible,andareavailablebecausePerforce’sdatabasecanbereplicatedintoarelationaldatabase.
10 Comparison: Perforce and Subversion
Table1:Resultsforequivalentversioningoperationsonasmalldataset(alltimeinseconds).
Operation Subversion (1.7) Perforce (2011.1)
Add tree 20.9 34.0
Lightweight branch 0.3 1.1
Delete tree 1.5 1.0
Label/tag tree 0.3 0.3
Merge edits to entire tree 73.1 16.4
Preview merge (no merge necessary) 4.3 0.2
Sync entire workspace 14.0 1.4
Preview sync (no updates necessary) 1.0 0.6
Restore deleted tree 32.0 36.1
BENCHMARKSPerforceeasilyoutperformsSubversioninallequivalentoperationsduringcomparativebenchmarkingtests.Notably,Subversionperformancedegradesconsiderablyasthenumberandsizeoffilesincreases.Thetestresultsaredetailedbelow.
Test PlatformThecombinedclient/servermachineonwhichthetestswererunhadthefollowingspecifications:
• AmazonEC2highmemoryquadrupleextralargeinstance
• Linuxx86_6464-bitRedHatEnterpriseLinux
• 26ECUs,8cores,68GBRAM
• P4D/LINUX26X86_64/2011.1.BETA/347706
• svn,version1.7.0(r1176462):CollabNetSubversionEdge-2.1.0_linux-x86_64
Test DataThetestdataforthesmallrunconsistedoftheApachewebserverandTomcatapplicationserversourcetrees,totaling46MBand4,480files.Themediumdatasetwasfourcopiesofthesmalldataset.Thelargedatasetcomprised207largebinaryfiles,totaling632MBinsize.
Test ResultsPerformanceresultsforthePerforceandSubversioncomparativebenchmarksarepresentedinthefollowingtables.Responsetimesweremeasuredinseconds.
11 Comparison: Perforce and Subversion
Table2:Resultsforequivalentversioningoperationsonamediumdataset(alltimeinseconds).
Operation Subversion (1.7) Perforce (2011.1)
Add tree 79.5 139.7
Lightweight branch 0.7 4.4
Delete tree 4.0 4.0
Label/tag tree 1.0 0.5
Merge edits to entire tree 283.4 62.5
Preview merge (no merge necessary) 11.2 0.4
Sync entire workspace 41.8 5.9
Preview sync (no updates necessary) 1.5 2.5
Restore deleted tree 161.8 160.9
Table3:Resultsforequivalentversioningoperationsonalarge(binary)dataset(alltimeinseconds).
Operation Subversion (1.7) Perforce (2011.1)
Add tree 44.2 51.8
Lightweight branch 0.1 0.8
Delete tree 1.5 1.0
Label/tag tree 0.1 <0.1
Merge edits to entire tree 62.5 10.7
Preview merge (no merge necessary) 3.5 <0.1
Sync entire workspace 62.7 9.4
Preview sync (no updates necessary) 1.0 <0.1
Restore deleted tree 63.0 48.9
12 Comparison: Perforce and Subversion
APPENDIX A: DETAILED BRANCHING AND MERGING ANALYSISThisappendixanalyzesseveralcommonproblemswithSubversionbranchingandmerging,withspecificexamples.TheanalysisisgroundedinasetofbranchingandmergingteststhatPerforcerunsinternallyasaregressionsuiteforitsownproduct.Perforcesuccessfullypassesallofthetestsdescribedhere.
Results SummaryOutof141tests,Subversionfailed20.SixothersarenotapplicablebecauseSubversiondoesnotsupportasmanyoptionsduringthemergeandresolveprocess.
Intended WorkflowSubversion’smergingcommandswereintendedtosupportabasicbranch-merge-promoteworkflow.Achildbranchiscreatedfornewwork.Changesfromtheparentareperiodicallymergeddowntokeepthechilduptodate.Whenworkonthechildbranchiscomplete,itispromotedtotheparentandretired.
Wheneveryoubeginworkingoutsidetheboundsofthatbasicworkflow,complexitiesappear:
• Reusingachildbranchrequiresadditionalsteps,asdescribedintheSubversiononlinebook.5
• Workingatthefileratherthanthedirectorylevelismuchmoredifficult.Forinstance,itisdifficulttoreferenceadeletedheadrevisioninSubversion,sopropagatingafiledeleteneedstohappenbymergingtheentiredirectory(andpossiblydealingwithatreeconflict).
• Mergebaseselectionisinefficientwhendealingwithladdermergesorindirectmergehistory,resultinginmoremergecomplexityandconflicts.
• Indirectmergehistoryissometimesignored.Previouslymergedorignoreddeltasmaybereintroduced.
• Subversion’smethodofreachingbranchconvergence,thereintegratemergeoption,isintendedforaveryspecificusecaseandcannotbeappliedelsewhere.IngeneralsituationsSubversionlacksacommandthatforcesconvergenceduringamerge.6
5http://svnbook.red-bean.com/en/1.6/svn.branchmerge.advanced.html#svn.branchmerge.advanced.
reintegratetwice
6Ifthereareconflictsduringamerge,Subversionallowseitherthesourceortargettobeacceptedinfullas
themergeresult.Butoddlyenoughiftherearenoconflictsthecontentswillalwaysbeautomaticallymerged.
Subversion’s Problems with Base Selection and Merge HistorySeveralfailureswereduetopoororinefficientbaseselection,whileotherswereduetofailuretoconsiderpriormergehistory.Subversionseemstofavorpickingamergebaseonthesourcebranch,evenifselectingabaseonthetarget(oranindirectlyrelated)branchwouldyieldamoreefficientmerge.
Insomecasespickingalessdesirablemergebasehaslittleornoeffectontheendresult.Butinsomecases,asdiscussedpriorinBranching,Merging,andReleaseManagement,pickingalessdesirablemergebasecausesmergeconflictsunnecessarily.Thebaseshouldbechosentoreflect,asmuchaspossible,anyexistingmergecredit—revisionsalreadyaccountedforinthemergetarget.Generallyspeaking,pickingamergebaseascloseaspossibletothesourceandtargetrevisionsyieldslessdeltastoconsider,reducingthechancesforconflictsandotherproblems.
Whenamergegivesconflictsandotherproblemswithoutavalidreason,orreintroducespreviouslyconsidereddeltas,usersloseconfidenceinthemergeengine.Besidesthetimeandefforttofixtheimmediateproblem,usersbecomemorelikelytomanuallyverifymerges,whichcanseverelyimpactproductivity.
Onarelatednote,Subversionquiteeasilyallowsmergingbetweenfilesordirectorieswithnoancestry.Subversion’smergecommandoriginallyhadtoassumenoinformationaboutmergeancestry,asSubversiondidnotoffermergetrackinguntilthe1.5release.Althoughbaselessmergesareoccasionallyuseful,theyshouldnotbeavailablewithoutspecificuseracknowledgement,inordertopreventaccidentalmerges.
Furtherexamplesofimproperbaseselectionandmergehistoryhandlingaredetailednext.
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