pgsql: Invent recursive_worktable_factor GUC to replace hard-wired cons

Invent recursive_worktable_factor GUC to replace hard-wired constant.

Up to now, the planner estimated the size of a recursive query's
worktable as 10 times the size of the non-recursive term. It's hard
to see how to do significantly better than that automatically, but
we can give users control over the multiplier to allow tuning for
specific use-cases. The default behavior remains the same.

Simon Riggs

Discussion: https://postgr.es/m/CANbhV-EuaLm4H3g0+BSTYHEGxJj3Kht0R+rJ8vT57Dejnh=_nA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0bd7af082ace135581bb13a6bd2d88e68c66a3e0

Modified Files
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doc/src/sgml/config.sgml | 23 +++++++++++++++++++++++
src/backend/optimizer/path/costsize.c | 8 +++++---
src/backend/utils/misc/guc.c | 12 ++++++++++++
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/include/optimizer/cost.h | 2 ++
src/include/optimizer/optimizer.h | 1 +
6 files changed, 44 insertions(+), 3 deletions(-)