Remove grotty use of disable_cost for TID scan plans.
Previously, the code charged disable_cost for CurrentOfExpr, and then
subtracted disable_cost from the cost of a TID path that used
CurrentOfExpr as the TID qual, effectively disabling all paths except
that one. Now, we instead suppress generation of the disabled paths
entirely, and generate only the one that the executor will actually
understand.
With this approach, we do not need to rely on disable_cost being
large enough to prevent the wrong path from being chosen, and we
save some CPU cycle by avoiding generating paths that we can't
actually use. In my opinion, the code is also easier to understand
like this.
Patch by me. Review by Heikki Linnakangas.
Discussion: http://postgr.es/m/591b3596-2ea0-4b8e-99c6-fad0ef2801f5@iki.fi
Branch
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master
Details
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https://git.postgresql.org/pg/commitdiff/e4326fbc60c44aab6df5849d3d67a0cba4c71cf2
Modified Files
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src/backend/optimizer/path/allpaths.c | 14 +++++++++---
src/backend/optimizer/path/costsize.c | 26 ----------------------
src/backend/optimizer/path/tidpath.c | 41 ++++++++++++++++++++++++++++++-----
src/include/optimizer/paths.h | 2 +-
4 files changed, 48 insertions(+), 35 deletions(-)