comparação - perforce x subversion

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


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.

http://svnbook.red-bean.com/en/1.6/svn.branchmerge.advanced.html#svn.branchmerge.advanced.moves


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).


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


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


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


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


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.


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.


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.


Table2:Resultsforequivalentversioningoperationsonamediumdataset(alltimeinseconds).


Add tree 79.5 139.7


Delete tree 4.0 4.0

Label/tag tree 1.0 0.5


Preview merge (no merge necessary) 11.2 0.4


Preview sync (no updates necessary) 1.5 2.5


Table3:Resultsforequivalentversioningoperationsonalarge(binary)dataset(alltimeinseconds).


Add tree 44.2 51.8


Delete tree 1.5 1.0

Label/tag tree 0.1 <0.1


Preview merge (no merge necessary) 3.5 <0.1


Preview sync (no updates necessary) 1.0 <0.1



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.

http://svnbook.red-bean.com/en/1.6/svn.branchmerge.advanced.html#svn.branchmerge.advanced.reintegratetwice

http://svnbook.red-bean.com/en/1.6/svn.branchmerge.advanced.html#svn.branchmerge.advanced.reintegratetwice

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