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Tom Lane b55722692b Improve planner's cost estimation in the presence of semijoins. ... If we have a semijoin, say SELECT * FROM x WHERE x1 IN (SELECT y1 FROM y) and we're estimating the cost of a parameterized indexscan on x, the number of repetitions of the indexscan should not be taken as the size of y; it'll really only be the number of distinct values of y1, because the only valid plan with y on the outside of a nestloop would require y to be unique-ified before joining it to x. Most of the time this doesn't make that much difference, but sometimes it can lead to drastically underestimating the cost of the indexscan and hence choosing a bad plan, as pointed out by David Kubečka. Fixing this is a bit difficult because parameterized indexscans are costed out quite early in the planning process, before we have the information that would be needed to call estimate_num_groups() and thereby estimate the number of distinct values of the join column(s). However we can move the code that extracts a semijoin RHS's unique-ification columns, so that it's done in initsplan.c rather than on-the-fly in create_unique_path(). That shouldn't make any difference speed-wise and it's really a bit cleaner too. The other bit of information we need is the size of the semijoin RHS, which is easy if it's a single relation (we make those estimates before considering indexscan costs) but problematic if it's a join relation. The solution adopted here is just to use the product of the sizes of the join component rels. That will generally be an overestimate, but since estimate_num_groups() only uses this input as a clamp, an overestimate shouldn't hurt us too badly. In any case we don't allow this new logic to produce a value larger than we would have chosen before, so that at worst an overestimate leaves us no wiser than we were before.		11 years ago
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backend	Improve planner's cost estimation in the presence of semijoins.	11 years ago
bin	Make operator precedence follow the SQL standard more closely.	11 years ago
common	Unlink static libraries before rebuilding them.	11 years ago
include	Improve planner's cost estimation in the presence of semijoins.	11 years ago
interfaces	Fix libpq test expected output file	11 years ago
makefiles	Revert haphazard pgxs makefile changes	11 years ago
pl	PL/Python: Fix regression tests for Python 3	11 years ago
port	Build fls.o only when AC_REPLACE_FUNCS so dictates via $(LIBOBJS).	11 years ago
template	Remove duplicate specification of -Ae for HP-UX C compiler.	11 years ago
test	Support default ACLs in get_object_address	11 years ago
timezone	Update time zone data files to tzdata release 2015a.	11 years ago
tools	Refactor Mkvcbuild.pm to facilitate modules migrations	11 years ago
tutorial	Update copyright for 2015	11 years ago
.gitignore	…
DEVELOPERS	…
Makefile	Create libpgcommon, and move pg_malloc et al to it	13 years ago
Makefile.global.in	Fix installcheck case for tap tests	11 years ago
Makefile.shlib	Unlink static libraries before rebuilding them.	11 years ago
bcc32.mak	…
nls-global.mk	Setup error context callback for transaction lock waits	12 years ago
win32.mak	…