什么是DDC（DerivedDataCache）？简单来说，是一些缓存文件。在使用Editor的过程中，有可能会在编辑某些文件，或者使用某些文件的时候产生额外的数据。
为了避免每次都需要重新产生一次数据，所以第一次产生完数据之后，会将数据序列化，并以缓存的形式保存下来。
DerivedDataCache目录包含了为引用的内容而生成的衍生数据文件。如果引用内容没有可用的缓存文件，则会极大增加载入时间。
DerivedDataCache代码
获取FDerivedDataCacheInterface全局单例对象
/*** UnrealEngine\Engine\Source\Runtime\Core\Public\Misc\CoreMisc.h ***/
/** Return the DDC interface, if it is available, otherwise return NULL **/
CORE_API class FDerivedDataCacheInterface* GetDerivedDataCache();
/** Return the DDC interface, fatal error if it is not available. **/
CORE_API class FDerivedDataCacheInterface& GetDerivedDataCacheRef();
// ---------------------------------------------------------------------------------------
/*** UnrealEngine\Engine\Source\Runtime\Core\Private\Misc\CoreMisc.cpp ***/
class FDerivedDataCacheInterface* GetDerivedDataCache()
{
static class FDerivedDataCacheInterface* SingletonInterface = NULL;
if (!FPlatformProperties::RequiresCookedData())
{
static bool bInitialized = false;
if (!bInitialized)
{
check(IsInGameThread());
bInitialized = true;
class IDerivedDataCacheModule* Module = FModuleManager::LoadModulePtr<IDerivedDataCacheModule>("DerivedDataCache");
if (Module)
{
SingletonInterface = &Module->GetDDC();
}
}
}
return SingletonInterface;
}
class FDerivedDataCacheInterface& GetDerivedDataCacheRef()
{
class FDerivedDataCacheInterface* SingletonInterface = GetDerivedDataCache();
if (!SingletonInterface)
{
UE_LOG(LogInit, Fatal, TEXT("Derived Data Cache was requested, but not available."));
CA_ASSUME( SingletonInterface != NULL ); // Suppress static analysis warning in unreachable code (fatal error)
}
return *SingletonInterface;
}
DerivedDataCache插件
将数据写入DDC缓存
/*** UnrealEngine\Engine\Source\Runtime\Engine\Private\Texture2D.cpp ***/
#if WITH_EDITORONLY_DATA uint32 FTexture2DMipMap::StoreInDerivedDataCache(const FString& InDerivedDataKey, const FStringView& TextureName) { int32 BulkDataSizeInBytes = BulkData.GetBulkDataSize(); check(BulkDataSizeInBytes > 0); TArray<uint8> DerivedData; FMemoryWriter Ar(DerivedData, /*bIsPersistent=*/ true); Ar << BulkDataSizeInBytes; { void* BulkMipData = BulkData.Lock(LOCK_READ_ONLY); Ar.Serialize(BulkMipData, BulkDataSizeInBytes); BulkData.Unlock(); } const uint32 Result = DerivedData.Num(); GetDerivedDataCacheRef().Put(*InDerivedDataKey, DerivedData, TextureName); DerivedDataKey = InDerivedDataKey; BulkData.RemoveBulkData(); return Result; } #endif // #if WITH_EDITORONLY_DATA
步骤如下：
① 创建一个TArray<uint8>类型的数组，用来存放要保存的数据
② 创建一个FMemoryWriter，构造的时候使用上面创建的数组
③ 往FMemoryWriter写入数据，可以使用<<符号压入数据，也可以使用Serialize()来压
④ 使用FDerivedDataCacheInterface::Put()将第一步创建的数组设置进DDC，注意注意DDC的Key需要遵循一定的规则，日后才能顺利地使用同一个Key重新取出
引擎中调用GetDerivedDataCacheRef().Put()函数的地方：
D:\svn\UnrealEngine\Engine\Plugins\Compositing\OpenColorIO\Source\OpenColorIO\Private\OpenColorIOShaderMap.cpp(347): GetDerivedDataCacheRef().Put(*GetOpenColorIOShaderMapKeyString(GetContent()->ShaderMapId, GetShaderPlatform()), SaveData, FStringView(*GetFriendlyName()));
D:\svn\UnrealEngine\Engine\Plugins\Editor\AssetSearch\Source\Private\AssetSearchManager.cpp(685): GetDerivedDataCacheRef().Put(*InDDCKey, IndexedJsonUTF8View, InAssetData.ObjectPath.ToString(), false);
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\NiagaraShader\Private\NiagaraShader.cpp(617): GetDerivedDataCacheRef().Put(*GetNiagaraShaderMapKeyString(GetContent()->ShaderMapId, GetShaderPlatform()), SaveData, FStringView(*GetFriendlyName()));
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraScript.cpp(1795): GetDerivedDataCacheRef().Put(*GetNiagaraDDCKeyString(), OutData, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSpriteRendererProperties.cpp(559): GetDerivedDataCacheRef().Put(*KeyString, Data, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystem.cpp(1815): GetDerivedDataCacheRef().Put(*DDCKey, OutData, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1592): GetDerivedDataCacheRef().Put(*DerivedDataKey, DerivedData, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1636): GetDerivedDataCacheRef().Put(*DerivedDataKey, DerivedData, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1708): GetDerivedDataCacheRef().Put(*DerivedDataKey, DerivedData, GetPathName());
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomBindingAsset.cpp(653): GetDerivedDataCacheRef().Put(*DerivedDataKey, DerivedData, GetPathName());
D:\svn\UnrealEngine\Engine\Source\Developer\PakFileUtilities\Private\PakFileUtilities.cpp(877): GetDerivedDataCacheRef().Put(*DDCKey, GetData, InFile.Dest);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\AudioDerivedData.cpp(243): GetDerivedDataCacheRef().Put(*DerivedDataKey, RawDerivedData, SoundWaveName);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\DistanceFieldAtlas.cpp(1289): GetDerivedDataCacheRef().Put(*Task->DDCKey, DerivedData, Task->StaticMesh->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Materials\MaterialShader.cpp(1172): GetDerivedDataCacheRef().Put(*GetMaterialShaderMapKeyString(ShaderMapId, GetShaderPlatform(), TargetPlatform), SaveData, FStringView(GetFriendlyName()));
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Particles\ParticleModules.cpp(1322): GetDerivedDataCacheRef().Put(*KeyString, Data, GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Particles\SubUVAnimation.cpp(123): GetDerivedDataCacheRef().Put(*KeyString, Data, GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\ShaderCompiler\ShaderCompiler.cpp(4813): GetDerivedDataCacheRef().Put(*GetGlobalShaderMapKeyString(ShaderMapId, Platform, TargetPlatform, ShaderFilenameDependencies.Value), SaveData, TEXT("GlobalShaderMap"_SV));
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\SkeletalMeshRenderData.cpp(359): GetDerivedDataCacheRef().Put(*BuiltDerivedDataKey, DerivedData, Owner->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\SoundWave.cpp(202): GetDerivedDataCacheRef().Put(*InDerivedDataKey, DerivedData, SoundWaveName);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp(2827): GetDerivedDataCacheRef().Put(*DerivedDataKey, DerivedData, Owner->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp(4577): GetDerivedDataCacheRef().Put(*MeshDataKey, DerivedData, GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Texture2D.cpp(171): GetDerivedDataCacheRef().Put(*InDerivedDataKey, DerivedData, TextureName);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\TextureDerivedData.cpp(763): GetDerivedDataCacheRef().Put(*DerivedDataKey, RawDerivedData, TextureName, /*bPutEvenIfExists*/ true);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\VT\VirtualTextureBuiltData.cpp(277): GetDerivedDataCacheRef().Put(*InDerivedDataKey, DerivedData, TextureName);
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\Landscape.cpp(3741): GetDerivedDataCacheRef().Put(*GetDDCKeyString(StateId), Bytes, Component->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\LandscapeCollision.cpp(1057): GetDerivedDataCacheRef().Put(*GetHFDDCKeyString(Format, bUseDefMaterial, HeightfieldGuid, InOutMaterials), OutCookedData, GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\LandscapeCollision.cpp(1283): GetDerivedDataCacheRef().Put(*GetHFDDCKeyString(Format, bUseDefMaterial, MeshGuid, InOutMaterials), OutCookedData, GetPathName());
读取DDC缓存
/*** UnrealEngine\Engine\Source\Runtime\Engine\Private\Streaming\Texture2DStreamIn_DDC.cpp ***/
#if WITH_EDITORONLY_DATA
// ... ...
void FTexture2DStreamIn_DDC::DoLoadNewMipsFromDDC(const FContext& Context)
{
if (Context.Texture && Context.Resource)
{
for (int32 MipIndex = PendingFirstLODIdx; MipIndex < CurrentFirstLODIdx && !IsCancelled(); ++MipIndex)
{
const FTexture2DMipMap& MipMap = *Context.MipsView[MipIndex];
check(MipData[MipIndex]);
if (!MipMap.DerivedDataKey.IsEmpty())
{
// The overhead of doing 2 copy of each mip data (from GetSynchronous() and FMemoryReader) in hidden by other texture DDC ops happening at the same time.
TArray<uint8> DerivedMipData;
bool bDDCValid = true;
const uint32 Handle = DDCHandles[MipIndex];
if (Handle)
{
bDDCValid = GetDerivedDataCacheRef().GetAsynchronousResults(Handle, DerivedMipData);
DDCHandles[MipIndex] = 0;
}
else
{
bDDCValid = GetDerivedDataCacheRef().GetSynchronous(*MipMap.DerivedDataKey, DerivedMipData, Context.Texture->GetPathName());
}
if (bDDCValid)
{
const int32 ExpectedMipSize = CalcTextureMipMapSize(MipMap.SizeX, MipMap.SizeY, Context.Resource->GetPixelFormat(), 0);
FMemoryReader Ar(DerivedMipData, true);
int32 MipSize = 0;
Ar << MipSize;
if (MipSize == ExpectedMipSize)
{
Ar.Serialize(MipData[MipIndex], MipSize);
}
else
{
UE_LOG(LogTexture, Error, TEXT("DDC mip size (%d) not as expected."), MipIndex);
MarkAsCancelled();
}
}
else
{
// UE_LOG(LogTexture, Warning, TEXT("Failed to stream mip data from the derived data cache for %s. Streaming mips will be recached."), Context.Texture->GetPathName() );
MarkAsCancelled();
}
}
else
{
UE_LOG(LogTexture, Error, TEXT("DDC key missing."));
MarkAsCancelled();
}
}
FPlatformMisc::MemoryBarrier();
}
}
#endif
步骤如下：
① 传入Key调用GetDerivedDataCacheRef.GetSynchronous()同步或GetDerivedDataCacheRef().GetAsynchronous()异步获取DDC数据。
② 得到TArray<uint8> DerivedMipData二进制数据块后，将这个数组传入到FMemoryWriter就可以反序列化出数据。
引擎中调用GetDerivedDataCacheRef().GetSynchronous同步函数的地方：
D:\svn\UnrealEngine\Engine\Plugins\Compositing\OpenColorIO\Source\OpenColorIO\Private\OpenColorIOShaderMap.cpp(312): if (GetDerivedDataCacheRef().GetSynchronous(*DataKey, CachedData, InColorTransform->GetFriendlyName()))
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\NiagaraShader\Private\NiagaraShader.cpp(584): if (GetDerivedDataCacheRef().GetSynchronous(*DataKey, CachedData, Script->GetFriendlyName()))
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraScript.cpp(1771): if (GetDerivedDataCacheRef().GetSynchronous(*GetNiagaraDDCKeyString(), OutData, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSpriteRendererProperties.cpp(545): if (GetDerivedDataCacheRef().GetSynchronous(*KeyString, Data, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\FX\Niagara\Source\Niagara\Private\NiagaraSystem.cpp(1837): if (GetDerivedDataCacheRef().GetSynchronous(*ScriptPair.CompiledScript->GetNiagaraDDCKeyString(), Data, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1523): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1617): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomAsset.cpp(1688): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Plugins\Runtime\HairStrands\Source\HairStrandsCore\Private\GroomBindingAsset.cpp(614): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Developer\Apple\MetalShaderFormat\Private\MetalShaderCompiler.cpp(1009): bSucceeded = GetDerivedDataCacheRef().GetSynchronous(BytecodeCooker, OutData, &bDataWasBuilt);
D:\svn\UnrealEngine\Engine\Source\Developer\Apple\MetalShaderFormat\Private\MetalShaderCompiler.cpp(1595): bool bCompiled = GetDerivedDataCacheRef().GetSynchronous(Cooker, OutData, &bDataWasBuilt) && OutData.Num();
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimCompressionDerivedData.cpp(331): GetDerivedDataCacheRef().GetSynchronous(&Compressor, OutData);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimSequence.cpp(2323): if (!bSkipDDC && GetDerivedDataCacheRef().GetSynchronous(*FinalDDCKey, OutData, AnimCompressor->GetDebugContextString()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimSequence.cpp(2353): const bool bSuccess = GetDerivedDataCacheRef().GetSynchronous(AnimCompressor, OutData, &bBuilt);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimStreamable.cpp(632): if (!bSkipDDC && GetDerivedDataCacheRef().GetSynchronous(*FinalDDCKey, OutData, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimStreamable.cpp(686): const bool bSuccess = GetDerivedDataCacheRef().GetSynchronous(AnimCompressor, OutData, &bBuilt);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\AudioDerivedData.cpp(533): if (!bForceRebuild && GetDerivedDataCacheRef().GetSynchronous(*DerivedData->DerivedDataKey, RawDerivedData, SoundWave.GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\AudioStreaming.cpp(71): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedChunkData, TEXT("Unknown Audio"_SV)))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\DistanceFieldAtlas.cpp(915): if (GetDerivedDataCacheRef().GetSynchronous(*InDDCKey, DerivedData, Mesh->GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Materials\MaterialShader.cpp(1138): if (CheckCache && GetDerivedDataCacheRef().GetSynchronous(*DataKey, CachedData, Material->GetFriendlyName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Particles\ParticleModules.cpp(1308): if (GetDerivedDataCacheRef().GetSynchronous(*KeyString, Data, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Particles\SubUVAnimation.cpp(109): if (GetDerivedDataCacheRef().GetSynchronous(*KeyString, Data, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\PhysicsEngine\BodySetup.cpp(1482): bDDCHit = GetDerivedDataCacheRef().GetSynchronous(&InBuilder, OutData, &bDataWasBuilt);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\SkeletalMeshRenderData.cpp(153): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, Owner->GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\SoundWave.cpp(967): bGetSuccessful = GetDerivedDataCacheRef().GetSynchronous(DeriveAudioData, OutData, &bDataWasBuilt);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp(2747): if (GetDerivedDataCacheRef().GetSynchronous(*DerivedDataKey, DerivedData, Owner->GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp(4286): if (GetDerivedDataCacheRef().GetSynchronous(*MeshDataKey, DerivedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Streaming\Texture2DStreamIn_DDC.cpp(181): bDDCValid = GetDerivedDataCacheRef().GetSynchronous(*MipMap.DerivedDataKey, DerivedMipData, Context.Texture->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\TextureDerivedDataTask.cpp(446): if (!bForceRebuild && GetDerivedDataCacheRef().GetSynchronous(*DerivedData->DerivedDataKey, RawDerivedData, Texture.GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Experimental\GeometryCollectionEngine\Private\GeometryCollection\GeometryCollectionObject.cpp(417): const bool bSuccess = GetDerivedDataCacheRef().GetSynchronous(GeometryCollectionCooker, DDCData, &bBuilt);
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\Landscape.cpp(3726): if (GetDerivedDataCacheRef().GetSynchronous(*GetDDCKeyString(StateId), Bytes, Component->GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\LandscapeCollision.cpp(884): if (GetDerivedDataCacheRef().GetSynchronous(*DDCKey, OutCookedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\LandscapeCollision.cpp(1114): if (GetDerivedDataCacheRef().GetSynchronous(*DDCKey, OutCookedData, GetPathName()))
D:\svn\UnrealEngine\Engine\Source\Runtime\NavigationSystem\Private\NavCollision.cpp(553): if (GetDerivedDataCacheRef().GetSynchronous(DerivedNavCollisionData, OutData, &bDataWasBuilt))
引擎中调用GetDerivedDataCacheRef().GetAsynchronous异步函数的地方：
D:\svn\UnrealEngine\Engine\Plugins\Editor\AssetSearch\Source\Private\AssetSearchManager.cpp(759): DDCRequest.DDCHandle = GetDerivedDataCacheRef().GetAsynchronous(*DDCRequest.DDCKey, DDCRequest.AssetData.ObjectPath.ToString());
D:\svn\UnrealEngine\Engine\Source\Developer\Apple\MetalShaderFormat\Private\MetalShaderCompiler.cpp(951): DebugInfoHandle = GetDerivedDataCacheRef().GetAsynchronous(DebugInfoCooker);
D:\svn\UnrealEngine\Engine\Source\Developer\PakFileUtilities\Private\PakFileUtilities.cpp(804): int32 AsyncHandle = GetDerivedDataCacheRef().GetAsynchronous(*DDCKey, InFile.Dest);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Animation\AnimCompressionDerivedData.cpp(344): uint32 AsyncHandle = GetDerivedDataCacheRef().GetAsynchronous(&Compressor);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\ShaderCompiler\ShaderCompiler.cpp(5050): AsyncDDCRequestHandles[HandleIndex] = GetDerivedDataCacheRef().GetAsynchronous(*DataKey, TEXT("GlobalShaderMap"_SV));
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\SoundWave.cpp(916): uint32 GetHandle = GetDerivedDataCacheRef().GetAsynchronous(DeriveAudioData);
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Streaming\Texture2DMipDataProvider_DDC.cpp(36): DDCHandles[MipIndex] = GetDerivedDataCacheRef().GetAsynchronous(*OwnerMip.DerivedDataKey, Context.Texture->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Engine\Private\Streaming\Texture2DStreamIn_DDC.cpp(126): DDCHandles[MipIndex] = GetDerivedDataCacheRef().GetAsynchronous(*MipMap.DerivedDataKey, Context.Texture->GetPathName());
D:\svn\UnrealEngine\Engine\Source\Runtime\Landscape\Private\LandscapeCollision.cpp(743): uint32 Handle = GetDerivedDataCacheRef().GetAsynchronous(*Key, GetPathName());
DDC Key
SkeletalMesh
MaterialShaderMap
#if WITH_EDITOR
/** Creates a string key for the derived data cache given a shader map id. */
static FString GetMaterialShaderMapKeyString(const FMaterialShaderMapId& ShaderMapId, EShaderPlatform Platform, const ITargetPlatform* TargetPlatform)
{
FName Format = LegacyShaderPlatformToShaderFormat(Platform);
FString ShaderMapKeyString = Format.ToString() + TEXT("_") + FString(FString::FromInt(GetTargetPlatformManagerRef().ShaderFormatVersion(Format))) + TEXT("_");
ShaderMapAppendKeyString(Platform, ShaderMapKeyString);
ShaderMapId.AppendKeyString(ShaderMapKeyString);
FMaterialAttributeDefinitionMap::AppendDDCKeyString(ShaderMapKeyString);
return FDerivedDataCacheInterface::BuildCacheKey(TEXT("MATSM"), MATERIALSHADERMAP_DERIVEDDATA_VER, *ShaderMapKeyString);
}
#endif // WITH_EDITOR
常见DDC类型和Key：
| 类型 | Key |
| GlobalShaderMap |
GSM_0875A72E4CE141409B09970FDA2C8978_PCD3D_ES31_8__BC5N_NOCCBN_NOIRIS_DEV_SL_P__62AA06E30D4FCE7BA88145D25DF42B52B74EAE5E |
| MaterialShaderMap |
MATSM_01BF92A5B29A44BE8A839E4251DA49D7_PCD3D_ES31_8__BC5N_NOCCBN_NOIRIS_DEV_SL__5522BBD10C8F3AF575C4915882212CE8BC12804E |
| NiagaraShaderMap |
NIAGARASM_34571112$2DFD93$2D4794$2DB613$2DCBEEF253AF84_SF_VULKAN_SM5_2334_2C74__D797E70ECED647A0932952F7D1E3185DC7BF40A7 |
| Texture |
TEXTURE_2D528FAD496A42E180956107C6FFBD67_BGRA8_748D4F054C3030AC8888BEA1993C93A__00BA9B04CB4EECFA96840E6DF67034D5C203C3FA |
| StaticMesh |
STATICMESH_14FB7BD55BAA4C14BCDC7C2AD14BCE50_228332BAE0224DD294E232B87D83948FQU__70371012EEFD9BD9DC1FA71BF73A89D39856A005 |
| SkeletalMesh | SKELETALMESH_7E02F227B356416F95DACCC99F757AD7_C62F737348494F34916095A57FF2EBF8__51148C90662BD28C223DB6E6B11DA54D5AEC97B9 |
| PhysX |
PHYSX_A08609EF508D460CBB6710540B03AACF_PHYSXPC_2681797E4C47F22E025D90A9BEAC2E4F__1_1_0_0_2_13315_0 |
| NavCollision | NAVCOLLISION_2983273BE5D6425391E8C0B3D1C0A55D_NAVCOLLISION_X_A40CFA28462BC7B14__84A663C6DA1450FB2CA08FD49BD4BB01532C8B31 |
| AnimSequence | ANIMSEQ_D8E26604610C43A4A2DCB8A690657705_0_3214C687B983834BB01F3466EF5B997F945__B53996C771A9C86F22CAE5417F8E3F80B1B8D8F0 |
| Particle（SubUV） | SUBUV__67E9AF86DF8B4D8E97B7A614A73CD4BF_44DD8757494DFEE554977DB47EF4041F_6_6_1_0$2E001000_V2 |
| NiagaraScript | NIAGARASCRIPTDERIVEDDATA_179023FDDDD444DE97F61296909C2990_2_17_6FC3CEC14F14B25__A626814BD4853484E8CAFEEF477D45777FC2788D |
| 。。。 。。。 | 。。。。。。 |
DDC缓存目录结构
本地DDC
本地DDC默认位置
Installed版本：
C:/Users/<user>/AppData/Local/UnrealEngine/Common/DerivedDataCache
源码版本：
D:\svn\UnrealEngine\Engine\DerivedDataCache // 本地DDC： 项目的派生数据。
iOS下Metal shader的DDC在：
UnrealEngine/Engine/Programs/ShaderCompileWorker/DDC
自定义本地DDC位置
可以通过在 DefaultEngine.ini 中添加一个部分来更改本地缓存位置。
以下示例将本地缓存移动到 Project\DerivedDataCache 下，而不是默认位置。
Installed版本：
[InstalledDerivedDataBackendGraph] Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=34, FoldersToClean=-1, Path="%GAMEDIR%DerivedDataCache")
源码版本：
[DerivedDataBackendGraph] Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=34, FoldersToClean=-1, Path="%GAMEDIR%DerivedDataCache")
注1：也可通过点击编辑器菜单Editor -- Editor Preferences...，在弹出面板的General -- Global标签中，设置Local Derived Data Cache路径
注2：将 UE-LocalDataCachePath（在Mac/Linux上为 UE_LocalDataCachePath）的环境变量设置为要使用的文件夹。如：setx UE-LocalDataCachePath d:\DDC
共享DDC
将DDC缓存文件放在可读写的高速网络共享磁盘上，让整个团队都能访问到，以避免每个人都需要在本地单独生成DDC造成的时间浪费和存储的空间浪费。
下文按照最优到最次的顺序列出了推荐方式。
-
在DefaultEngine.ini中覆盖你的项目设置（如下图所示），该覆盖项会将路径设置为团队的有效位置。
[DerivedDataBackendGraph] Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=10, MaxFileChecksPerSec=1, ConsiderSlowAt=70, PromptIfMissing=false, Path=\\YourCompanyServer\DDC, EnvPathOverride=UE-SharedDataCachePath, EditorOverrideSetting=SharedDerivedDataCache)
-
将
UE-SharedDataCachePath（在Mac/Linux上为UE_SharedDataCachePath）的环境变量设置为要使用的文件夹。注：永远不要将UE-SharedDataCachePath设置为本地路径！这样做意味着你将同时占用计算机上的本地缓存和共享缓存——两倍的磁盘空间占用量，且收益为零！net use \\YourCompanyServer\DDC "password" /user:"admin" /persistent:yes // windows上映射网络驱动器 setx UE-SharedDataCachePath \\YourCompanyServer\DDC // 设置用户环境变量UE-SharedDataCachePath为\\YourCompanyServer\DDC
-
通过点击编辑器菜单Editor -- Editor Preferences...，在弹出面板的General -- Global标签中，设置Shared Derived Data Cache路径.
禁用共享DDC
当网速慢的时候，访问DDC数据比自己生成DDC数据花费的时间更长，这个时候可以禁用掉共享DDC。
请使用以下方法之一：
-
在命令行上传递-ddc=noshared。
-
将环境变量设置为UE-SharedDataCachePath=None（在Mac/Linux上：UE_SharedDataCachePath=None）
构建DDC缓存
可以在构建机上每夜定时执行此操作，以确保DDC缓存始终处于就绪状态，提升团队的工作效率。
D:\svn\UnrealEngine\Engine\Binaries\Win64\UE4Editor.exe MyGame -run=DerivedDataCache -fill
DDC Pak
如果你从Epic Games商店下载虚幻引擎，则该引擎将附带DDC Pak (.ddp)。
DDC Pak包含所有引擎内容的派生数据，因此你无需编译着色器等就可以开始工作。同样，出于相同原因，一些示例也随DDC Pak一起提供。
引擎DDC Pak：EngineDir/DerivedDataCache/Compressed.ddp
项目DDC Pak：ProjectDir/DerivedDataCache/Compressed.ddp
创建DDC Pak
引擎DDC Pak：UE4Editor.exe -run=DerivedDataCache -fill -DDC=CreatePak
项目DDC Pak：UE4Editor.exe MyGame -run=DerivedDataCache -fill -DDC=CreatePak
注1：这会在UE4\MyGame\DerivedDataCache目录中创建DDC.ddp文件
注2：引擎将自动检测和使用.ddp文件
启动DDC
加载到内存中以便提升启动时间的启动文件
Installed版本：
C:/Users/<user>/AppData/Local/UnrealEngine/4.26/DerivedDataCache/Boot.ddc
源码版本：
D:\svn\MyGame\DerivedDataCache
DDC配置
DDC配置存放在UnrealEngine\Engine\Config\BaseEngine.ini相关的标签中，可在项目的DefaultEngine.ini中改写这些配置。
; Derived Data backend graphs
; Each of the below backend graph sections contains a set of nodes used to create derived data backed graph.
; DerivedDataBackendGraph is the default graph for source builds, and InstalledDerivedDataBackendGraph is the default for installed builds.
; Others can be specified othe command line using:
; -DDC=GraphSectionName (for example: -DDC=VerifyDerivedDataBackendGraph)
; Each graph should start with 'Root' node. Names of all the other nodes are not predefined.
; Supported node types are: KeyLength, AsyncPut, Hierarchical, Boot, Filesystem, ReadPak, WritePak, Verify
; The order nodes are define in is not relevant
; Filesystem backends can be disabled by setting the corresponding environment variable to 'None'. E.g UE-SharedDataCachePath=None
[DerivedDataBackendGraph]
; Keep files for at least 7 days 保留文件至少7天
MinimumDaysToKeepFile=7
; Configure the root entry. It uses a KeyLength node to hash long strings then passes requests to AsyncPut 配置根条目。它使用KeyLength节点对长字符串进行哈希处理，然后将请求传递给AsyncPut
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
; Configure the AsyncPut entry. It uses an AsyncPut node that then passes requests to Hierarchy 配置AsyncPut条目。它使用AsyncPut节点，然后将请求传递到层级
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
; Configure the hierarchy entry. This uses multiple nodes that are used in order until a read is found (writes go to all writable entries) 配置层级条目。这将使用多个节点，这些节点按顺序使用，直到找到读取内容（写入将转到所有可写条目）
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=Pak, Inner=EnginePak, Inner=Local, Inner=Shared)
; Configure the Boot node. This holds 512MB of data used to speed up booting. 配置Boot节点。这将保留用于加速启动的512MB数据
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
; Configure the local node. This is a filesystem node with the following set - 配置本地节点。这是具有以下设置的filesystem节点
; Readonly: Can data be written to this layer 能否将数据写入此层
; Clean: Perform a cleanup of old files on launch 在启动时执行旧文件清理
; Flush: Nuke the DDC and start over 破坏DDC并重新开始
; PurgeTransient: Don't keep transient data in the DDC 不要将瞬态数据保留在DDC中
; DeleteUnused: Clean up old files (happens on a background thread) 清理旧文件（在后台线程上进行）
; UnusedFileAge: Age after which files are removed 文件删除前保留时长
; FoldersToClean: Max number of folders to clean in a session. -1 = Unlimited 会话中要清除的最大文件夹数。-1 = 无限
; PromptIfMissing: If the path does not exist a warning prompt will be shown. This is useful for shared DDCs where the mount may have dropped
; ConsiderSlowAt: If access times are < this value in ms then some operations will be disabled to improve performance.
; MaxFileChecksPerSec: How many files to check a second. 每秒检查的文件数量。
; Path: path to use for the filesystem DDC 文件系统DDC使用的路径
; EnvPathOverride: An environment variable that if set will be used instead of path. E.g. UE-LocalDataCachePath=d:\DDC. ('None' disables the DDC) 环境变量，如果设置，将用于代替路径。如UE-LocalDataCachePath=d:\DDC。（ 'None' 会禁用DDC）
; CommandLineOverride: A command line argument used in preference to the default / envvar setting. E.g. -SharedDataCachePath=\\someshare\folder 优先于默认值/envvar设置使用的命令行参数。如-SharedDataCachePath=\\someshare\folder
; EditorOverrideSetting: Editor user setting that overrides the default/envvarcommand line values 覆盖默认/envvar/命令行值的编辑器用户设置
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, PromptIfMissing=true, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath, EditorOverrideSetting=LocalDerivedDataCache)
; Configure the shared DDC that is accessed after local. It's a filesystem DDC and the parameters are explained above 配置在本地之后访问的共享DDC。这是文件系统DDC，上面已经说明参数
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=true, UnusedFileAge=6, FoldersToClean=10, MaxFileChecksPerSec=1, ConsiderSlowAt=70, PromptIfMissing=false, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath, EditorOverrideSetting=SharedDerivedDataCache, CommandLineOverride=SharedDataCachePath)
; Configure an alternate shared DDC that is accessed after local. It's a filesystem DDC and the parameters are explained above 配置在本地之后访问的替代共享DDC。这是文件系统DDC，上面已经说明参数
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=true, UnusedFileAge=8, FoldersToClean=10, MaxFileChecksPerSec=1, ConsiderSlowAt=70, PromptIfMissing=false, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
; Configure a Project Pak node. This is a pre-generated DDC data file for the project that can be distributed to reduce runtime fetches/generation 配置Project Pak节点。这是项目的预生成DDC数据文件，可以发布该文件以便减少运行时获取/生成
; See documentation for how to create a DDP via the DerivedDataCache commandlet 请参阅文档，了解如何通过DerivedDataCache Commandlet创建DDP
Pak=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
; Configure a Project Pak node. This is a pre-generated DDC data file for the engine that can be distributed to reduce runtime fetches/generation 配置Project Pak节点。这是引擎的预生成DDC数据文件，可以分发该文件以便减少运行时获取/生成
EnginePak=(Type=ReadPak, Filename=%ENGINEDIR%DerivedDataCache/DDC.ddp)
[DerivedDataBackendGraph_Fill_Seattle]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=Pak, Inner=EnginePak, Inner=Local, Inner=Seattle)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache)
Seattle=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=true, UnusedFileAge=8, FoldersToClean=10, MaxFileChecksPerSec=1, Path=?EpicSeaDDC, EnvPathOverride=UE-SharedDataCachePath_Seattle)
Pak=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
EnginePak=(Type=ReadPak, Filename=%ENGINEDIR%DerivedDataCache/DDC.ddp)
[InstalledDerivedDataBackendGraph]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=Pak, Inner=CompressedPak, Inner=EnginePak, Inner=EnterprisePak, Inner=Local, Inner=Shared)
Boot=(Type=Boot, Filename="%ENGINEUSERDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path="%ENGINEVERSIONAGNOSTICUSERDIR%DerivedDataCache", EditorOverrideSetting=LocalDerivedDataCache)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=true, UnusedFileAge=6, FoldersToClean=10, MaxFileChecksPerSec=1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath, EditorOverrideSetting=SharedDerivedDataCache)
Pak=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
CompressedPak=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/Compressed.ddp", Compressed=true)
EnginePak=(Type=ReadPak, Filename=../../../Engine/DerivedDataCache/Compressed.ddp, Compressed=true)
EnterprisePak=(Type=ReadPak, Filename=../../../Enterprise/DerivedDataCache/Compressed.ddp, Compressed=true)
[NoShared]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=Pak, Inner=Local)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath)
Pak=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
[CreatePak]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=PakWrite, Inner=PakRead, Inner=Local, Inner=Shared)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=6, FoldersToClean=-1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath)
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=6, FoldersToClean=-1, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
PakRead=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
PakWrite=(Type=WritePak, Filename="%GAMEDIR%DerivedDataCache/DDC.ddp")
[CreateInstalledProjectPak]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=EnginePak, Inner=PakWrite, Inner=PakRead, Inner=Local, Inner=Shared)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath, CommandLineOverride=SharedDataCachePath)
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
EnginePak=(Type=ReadPak, Filename=../../../Engine/DerivedDataCache/Compressed.ddp, Compressed=true)
PakRead=(Type=ReadPak, Filename="%GAMEDIR%DerivedDataCache/Compressed.ddp", Compressed=true)
PakWrite=(Type=WritePak, Filename="%GAMEDIR%DerivedDataCache/Compressed.ddp", Compressed=true)
[CreateInstalledEnginePak]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=PakWrite, Inner=Local, Inner=Shared)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath)
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
PakWrite=(Type=WritePak, Filename=%ENGINEDIR%DerivedDataCache/Compressed.ddp, Compressed=true)
[CreateInstalledEnterprisePak]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Boot, Inner=PakWrite, Inner=Local, Inner=Shared)
Boot=(Type=Boot, Filename="%GAMEDIR%DerivedDataCache/Boot.ddc", MaxCacheSize=512)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath)
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
PakWrite=(Type=WritePak, Filename=../../../Enterprise/DerivedDataCache/Compressed.ddp, Compressed=true)
[CreateProjectCache]
MinimumDaysToKeepFile=7
Root=(Type=KeyLength, Length=120, Inner=AsyncPut)
AsyncPut=(Type=AsyncPut, Inner=Hierarchy)
Hierarchy=(Type=Hierarchical, Inner=Local, Inner=Project, Inner=Shared)
Local=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%ENGINEDIR%DerivedDataCache, EnvPathOverride=UE-LocalDataCachePath)
Project=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=true, PurgeTransient=true, DeleteUnused=true, UnusedFileAge=10, FoldersToClean=-1, Path=%GAMEDIR%ProjectDerivedData)
Shared=(Type=FileSystem, ReadOnly=false, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC, EnvPathOverride=UE-SharedDataCachePath)
AltShared=(Type=FileSystem, ReadOnly=true, Clean=false, Flush=false, DeleteUnused=false, UnusedFileAge=8, FoldersToClean=-1, Path=?EpicDDC2, EnvPathOverride=UE-SharedDataCachePath2)
[VirtualTextureChunkDDCCache]
UnusedFileAge=10
MaxFileChecksPerSec=-1 ;no limit
Path=%GAMEDIR%DerivedDataCache/VT
[DDCCleanup]
TimeToWaitAfterInit=120
TimeBetweenDeleteingDirectories=5
TimeBetweenDeletingFiles=2
注1：可在 DefaultEngine.ini 中创建新的[YourDDCSettings]条目的DDC配置，然后使用 -ddc=YourDDCSettings 运行编辑器来使用自定义DDC配置。
注2：也可以使用DefaultEngine.ini 中已定义好的DDC配置，如[NoShared]，使用-ddc=NoShared来运行编辑器
DDC日志
[2023.09.22-10.43.59:750][ 0]LogDerivedDataCache: Display: |DerivedDataBackends.cpp:774|Max Cache Size: 512 MB [2023.09.22-10.43.59:808][ 0]LogDerivedDataCache: |MemoryDerivedDataBackend.cpp:306|Loaded boot cache 0.06s 91MB ../../../../MyGame/DerivedDataCache/Boot.ddc. [2023.09.22-10.43.59:808][ 0]LogDerivedDataCache: Display: |DerivedDataBackends.cpp:792|Loaded Boot cache: ../../../../MyGame/DerivedDataCache/Boot.ddc [2023.09.22-10.43.59:808][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:288|FDerivedDataBackendGraph: Pak pak cache file ../../../../MyGame/DerivedDataCache/DDC.ddp not found, will not use a pak cache. [2023.09.22-10.43.59:808][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:459|Unable to find inner node Pak for hierarchical cache Hierarchy. [2023.09.22-10.43.59:808][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:288|FDerivedDataBackendGraph: EnginePak pak cache file ../../../Engine/DerivedDataCache/DDC.ddp not found, will not use a pak cache. [2023.09.22-10.43.59:809][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:459|Unable to find inner node EnginePak for hierarchical cache Hierarchy. [2023.09.22-10.43.59:829][ 0]LogDerivedDataCache: |FileSystemDerivedDataBackend.cpp:404|Speed tests for ../../../Engine/DerivedDataCache took 0.02 seconds [2023.09.22-10.43.59:829][ 0]LogDerivedDataCache: Display: |FileSystemDerivedDataBackend.cpp:176|Performance to ../../../Engine/DerivedDataCache: Latency=0.02ms. RandomReadSpeed=236.07MBs, RandomWriteSpeed=59.80MBs. Assigned SpeedClass 'Local' [2023.09.22-10.43.59:832][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:605|Using Local data cache path ../../../Engine/DerivedDataCache: Writable [2023.09.22-10.43.59:832][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:569|Shared data cache path not found in *engine.ini, will not use an Shared cache. [2023.09.22-10.43.59:833][ 0]LogDerivedDataCache: |DerivedDataBackends.cpp:459|Unable to find inner node Shared for hierarchical cache Hierarchy. 。。。 [2023.09.22-10.44.37:323][ 0]LogDerivedDataCache: |MemoryDerivedDataBackend.cpp:197|Saved boot cache 0.05s 91MB ../../../../MyGame/DerivedDataCache/Boot.ddc.
注：通过加-logcmds="LogDerivedDataCache Verbose"参数来运行编辑器，可以打印更详细的DDC日志
参考
简单了解Unreal Engine中的DDC(Derived Data Cache)
标签：Engine,缓存,false,UnrealEngine,GetDerivedDataCacheRef,cpp,DDC,UE4 From： https://www.cnblogs.com/kekec/p/16332933.html