mirror of
https://github.com/postgres/postgres.git
synced 2025-09-08 00:47:37 +03:00
d7a6a04dc7
constants through full joins, as in select * from tenk1 a full join tenk1 b using (unique1) where unique1 = 42; which should generate a fairly cheap plan where we apply the constraint unique1 = 42 in each relation scan. This had been broken by my patch of 2008-06-27, which is now reverted in favor of a more invasive but hopefully less incorrect approach. That patch was meant to prevent incorrect extraction of OR'd indexclauses from OR conditions above an outer join. To do that correctly we need more information than the outerjoin_delay flag can provide, so add a nullable_relids field to RestrictInfo that records exactly which relations are nulled by outer joins that are underneath a particular qual clause. A side benefit is that we can make the test in create_or_index_quals more specific: it is now smart enough to extract an OR'd indexclause into the outer side of an outer join, even though it must not do so in the inner side. The old coding couldn't distinguish these cases so it could not do either.
$PostgreSQL: pgsql/src/backend/nodes/README,v 1.4 2008/08/25 22:42:32 tgl Exp $
Node Structures
===============
Andrew Yu (11/94)
Introduction
------------
The current node structures are plain old C structures. "Inheritance" is
achieved by convention. No additional functions will be generated. Functions
that manipulate node structures reside in this directory.
FILES IN THIS DIRECTORY (src/backend/nodes/)
General-purpose node manipulation functions:
copyfuncs.c - copy a node tree
equalfuncs.c - compare two node trees
outfuncs.c - convert a node tree to text representation
readfuncs.c - convert text representation back to a node tree
makefuncs.c - creator functions for some common node types
nodeFuncs.c - some other general-purpose manipulation functions
Specialized manipulation functions:
bitmapset.c - Bitmapset support
list.c - generic list support
params.c - Param support
tidbitmap.c - TIDBitmap support
value.c - support for Value nodes
FILES IN src/include/nodes/
Node definitions:
nodes.h - define node tags (NodeTag)
primnodes.h - primitive nodes
parsenodes.h - parse tree nodes
plannodes.h - plan tree nodes
relation.h - planner internal nodes
execnodes.h - executor nodes
memnodes.h - memory nodes
pg_list.h - generic list
Steps to Add a Node
-------------------
Suppose you wanna define a node Foo:
1. Add a tag (T_Foo) to the enum NodeTag in nodes.h. (If you insert the
tag in a way that moves the numbers associated with existing tags,
you'll need to recompile the whole tree after doing this. It doesn't
force initdb though, because the numbers never go to disk.)
2. Add the structure definition to the appropriate include/nodes/???.h file.
If you intend to inherit from, say a Plan node, put Plan as the first field
of your struct definition.
3. If you intend to use copyObject, equal, nodeToString or stringToNode,
add an appropriate function to copyfuncs.c, equalfuncs.c, outfuncs.c
and readfuncs.c accordingly. (Except for frequently used nodes, don't
bother writing a creator function in makefuncs.c) The header comments
in those files give general rules for whether you need to add support.
4. Add cases to the functions in nodeFuncs.c as needed. There are many
other places you'll probably also need to teach about your new node
type. Best bet is to grep for references to one or two similar existing
node types to find all the places to touch.
Historical Note
---------------
Prior to the current simple C structure definitions, the Node structures
used a pseudo-inheritance system which automatically generated creator and
accessor functions. Since every node inherited from LispValue, the whole thing
was a mess. Here's a little anecdote:
LispValue definition -- class used to support lisp structures
in C. This is here because we did not want to totally rewrite
planner and executor code which depended on lisp structures when
we ported postgres V1 from lisp to C. -cim 4/23/90