[GitHub] [spark] steveloughran commented on pull request #41105: [SPARK-43403][UI] Ensure old SparkUI in HistoryServer has been detached before loading new one

["steveloughran (via GitHub)" <gi...@apache.org>]

steveloughran commented on PR #41105:
URL: https://github.com/apache/spark/pull/41105#issuecomment-1542317728

   don't remember the cache stuff, sorry. I know we have a problem in hadoop where cache lookup can trigger >1 fs creation and the same time, and if that is slow then at best: needless work, at worst: conflict and sometimes failures. so we use a semaphore to limit the #of threads which can create a new FS at the same time (HADOOP-17313). spark/tez workers and cloud stores doing network IO in initialize() are the troublespot here, FWIW.


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