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- Skew can cause a lot of problems
- Sufficient skew in the underlying data causes
load imbalances in the resulting parallel join
swamping the gains due to parallelism
- Earlier Skew handling algos perform worse
than
simple algos in the absence of skew
- There is no evidence that extreme degrees of
skew
occur commonly in practice
- Requirement to not penalize normal cases
much and
also handle extreme cases reasonably
- Paper presents several algos to do this
- Sampling is the main new ingredient
DBMS
1999-03-11