configs

config/spark/tmp/about.txt

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+# What is this directory?
+
+* In order to perform certain functions, spark sometimes needs to write temporary data to the disk. 
+* Previously, a temporary directory provided by the operating system was used for this purpose. 
+* However, this proved to be unreliable in some circumstances, so spark now stores temporary data here instead!
+
+spark will automatically cleanup the contents of this directory. 
+(but if for some reason it doesn't, if the server is stopped, you can freely delete any files ending in .tmp)
+
+tl;dr: spark uses this folder to store some temporary data.