I am working on SPARK-1529. I ran into an issue with my change, where the same shuffle file was being reused across 2 jobs. Please note this only happens when I use a hard coded location to use for shuffle files, say "/tmp". It does not happen with normal code path that uses DiskBlockManager to pick different directories for each run. So I want to understand how DiskBlockManager guarantees that such a conflict will never happen.
Let's say the shuffle block id has a value of shuffle_0_0_0. So the data file name is shuffle_0_0_0.data and index file name is shuffle_0_0_0.index. If I run a spark job twice, one after another, these files get created under different directories because of the hashing logic in DiskBlockManager. But the hash is based off the file name, so how are we sure that there won't be a conflict ever? -- Kannan
