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Why does one task run twenty minutes when the rest finish in one?
What you'll have at the end
A salted join where no single task's runtime dwarfs the rest of the stage
You need
A PySpark join between two tables, neither one small enough to broadcast, where one task is already taking far longer than the rest to finish, and you know the exact key value behind it along with roughly how many rows carry it.
Not covered
Diagnosing which key is skewed and by how much in the first place, and a join where the smaller side genuinely fits in memory: both of those are different jobs entirely.
Leans on
Catch a skewed join key before it stalls a distributed job
run that check first, before writing any join, to confirm which key is hot and by how much before salting it.
Speed up a fact-to-dimension join with a broadcast join
when the smaller side genuinely fits in memory, broadcasting it removes the shuffle a skewed key could ever land in, and this salted join isn't needed at all.
Checked 25 Aug 2026
Part of the PySpark cookbook