Arnold can generate a log reporting all the steps needed to render an image and any warnings and errors encountered by the renderer. This log also provides detailed statistics that are useful for debugging, optimizing, and benchmarking renders. Note that an individual log file will be saved for each frame of animation that has been rendered.
Write Log file also found under File->Preferences, Rendering Tab, Messages group.
Verbosity Level
Specifies the amount of information in the log messages, with Warnings being least and Debug most:
Console
Messages are logged in the Render Message Window.
Log File
If enabled a log is written to the specified file.
Max. Warnings
Limits the number of warning messages (of a similar type) that are sent to the log.
Detailed Texture Statistics
Enable very useful per texture statistics, with time spent on texture queries, amount of texture data read, memory consumption, etc.