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 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