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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master

Details
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https://git.postgresql.org/pg/commitdiff/a547e6867527ca16628a3fb1cf3ef6f785210a31

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