pgsql: Adjust cost model for HashAgg that spills to disk.

Adjust cost model for HashAgg that spills to disk.

Tomas Vondra observed that the IO behavior for HashAgg tends to be
worse than for Sort. Penalize HashAgg IO costs accordingly.

Also, account for the CPU effort of spilling the tuples and reading
them back.

Discussion: https://postgr.es/m/20200906212112.nzoy5ytrzjjodpfh@development
Reviewed-by: Tomas Vondra
Backpatch-through: 13

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b61d048e0d480f4311c62bf3026879c83ba9aaad

Modified Files
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src/backend/optimizer/path/costsize.c | 13 +++++++++++++
1 file changed, 13 insertions(+)