19a541143a
Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering. |
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| .. | ||
| adminpack | ||
| auth_delay | ||
| auto_explain | ||
| btree_gin | ||
| btree_gist | ||
| chkpass | ||
| citext | ||
| cube | ||
| dblink | ||
| dict_int | ||
| dict_xsyn | ||
| earthdistance | ||
| file_fdw | ||
| fuzzystrmatch | ||
| hstore | ||
| hstore_plperl | ||
| hstore_plpython | ||
| intagg | ||
| intarray | ||
| isn | ||
| lo | ||
| ltree | ||
| ltree_plpython | ||
| oid2name | ||
| pageinspect | ||
| passwordcheck | ||
| pg_buffercache | ||
| pg_freespacemap | ||
| pg_prewarm | ||
| pg_standby | ||
| pg_stat_statements | ||
| pg_trgm | ||
| pgcrypto | ||
| pgrowlocks | ||
| pgstattuple | ||
| postgres_fdw | ||
| seg | ||
| sepgsql | ||
| spi | ||
| sslinfo | ||
| start-scripts | ||
| tablefunc | ||
| tcn | ||
| test_decoding | ||
| tsearch2 | ||
| tsm_system_rows | ||
| tsm_system_time | ||
| unaccent | ||
| uuid-ossp | ||
| vacuumlo | ||
| xml2 | ||
| Makefile | ||
| README | ||
| contrib-global.mk | ||
README
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.