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586b98fdf1
The "name" comparison operators now all support collations, making them
functionally equivalent to "text" comparisons, except for the different
physical representation of the datatype. They do, in fact, mostly share
the varstr_cmp and varstr_sortsupport infrastructure, which has been
slightly enlarged to handle the case.
To avoid changes in the default behavior of the datatype, set name's
typcollation to C_COLLATION_OID not DEFAULT_COLLATION_OID, so that
by default comparisons to a name value will continue to use strcmp
semantics. (This would have been the case for system catalog columns
anyway, because of commit 6b0faf723, but doing this makes it true for
user-created name columns as well. In particular, this avoids
locale-dependent changes in our regression test results.)
In consequence, tweak a couple of places that made assumptions about
collatable base types always having typcollation DEFAULT_COLLATION_OID.
I have not, however, attempted to relax the restriction that user-
defined collatable types must have that. Hence, "name" doesn't
behave quite like a user-defined type; it acts more like a domain
with COLLATE "C". (Conceivably, if we ever get rid of the need for
catalog name columns to be fixed-length, "name" could actually become
such a domain over text. But that'd be a pretty massive undertaking,
and I'm not volunteering.)
Discussion: https://postgr.es/m/15938.1544377821@sss.pgh.pa.us
src/backend/nodes/README
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 want to 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