On each and every open of the material editor, shader compiler threads are triggered, even if just opening materials without doing any changes.
Also switching on/off LivePreview kicks off compiler threads (I usually keep this disabled).
For performance reasons and energy savings, I disable any “realtime” stuff, so even in content browser, I disabled the “Real Time Thumbnails”.
These compiles are triggered by missed cache shader maps
LogAssetEditorSubsystem: Opening Asset editor for Material /Game/WaterHFCM/M_HerbWater_6.M_HerbWater_6
LogMaterial: Display: Missing cached shader map for material M_HerbWater_6, compiling.
LogMaterial: Display: Missing cached shader map for material M_HerbWater_6, compiling.
LogMaterial: Display: Missing cached shader map for material M_HerbWater_6, compiling.
LogShaderCompilers: Display: Worker (1/5): shaders left to compile 45
...
LogShaderCompilers: Display: Worker (4/5): shaders left to compile 42
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionTextureSampleParameter2D_0, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionTextureSampleParameter2D_1, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionTextureSampleParameter2D_2, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionConstant3Vector_0, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionConstant3Vector_1, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionVectorParameter_1, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionVectorParameter_2, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionVectorParameter_3, compiling.
LogMaterial: Display: Missing cached shader map for material FMatExpressionPreview MaterialExpressionVectorParameter_4, compiling.
LogShaderCompilers: Display: Worker (1/5): shaders left to compile 77
LogSlate: Took 0.018542 seconds to synchronously load lazily loaded font '../../../Engine/Content/Slate/Fonts/Roboto-BoldCondensed.ttf' (158K)
LogShaderCompilers: Display: Worker (4/5): shaders left to compile 76
...
LogShaderCompilers: Display: Worker (1/5): shaders left to compile 72
LogSlate: Took 0.002019 seconds to synchronously load lazily loaded font '../../../Engine/Content/Slate/Fonts/Roboto-Italic.ttf' (157K)
LogShaderCompilers: Display: Worker (1/5): shaders left to compile 71
...
LogShaderCompilers: Display: Worker (1/5): shaders left to compile 18
MaterialEditorStats: Base pass shader: 549 instructions
MaterialEditorStats: Base pass shader with Volumetric Lightmap: 637 instructions
MaterialEditorStats: Base pass vertex shader: 162 instructions
MaterialEditorStats: Texture samplers: 7/16
MaterialEditorStats: Texture Lookups (Est.): VS(0), PS(6)
LogShaderCompilers: Display: Worker (4/5): shaders left to compile 17
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LogShaderCompilers: Display: Worker (2/5): shaders left to compile 1