mirror of
https://github.com/postgres/postgres.git
synced 2026-04-08 02:35:51 -04:00
4914b70847
outer join clauses. Given, say, ... from a left join b on a.a1 = b.b1 where a.a1 = 42; we'll deduce a clause b.b1 = 42 and then mark the original join clause redundant (we can't remove it completely for reasons I don't feel like squeezing into this log entry). However the original implementation of that wasn't bulletproof, because clause_selectivity() wouldn't honor this_selec if given nonzero varRelid --- which in practice meant that it worked as desired *except* when considering index scan quals. Which resulted in bogus underestimation of the size of the indexscan result for an inner indexscan in an outer join, and consequently a possibly bad choice of indexscan vs. bitmap scan. Fix by introducing an explicit test into clause_selectivity(). Also, to make sure we don't trigger that test in corner cases, change the convention to be that this_selec > 1, not this_selec = 1, means it's been marked redundant. Per trouble report from Scara Maccai. Back-patch to 8.2, where the problem was introduced. |
||
|---|---|---|
| .. | ||
| bitmapset.c | ||
| copyfuncs.c | ||
| equalfuncs.c | ||
| list.c | ||
| Makefile | ||
| makefuncs.c | ||
| nodeFuncs.c | ||
| nodes.c | ||
| outfuncs.c | ||
| params.c | ||
| print.c | ||
| read.c | ||
| readfuncs.c | ||
| README | ||
| tidbitmap.c | ||
| value.c | ||
*******************************************************************************
* *
* EXPLANATION OF THE NODE STRUCTURES *
* - Andrew Yu (11/94) *
* *
* Copyright (c) 1994, Regents of the University of California *
* *
* $PostgreSQL: pgsql/src/backend/nodes/README,v 1.2 2003/11/29 22:39:45 pgsql Exp $
* *
*******************************************************************************
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
Node manipulation functions:
copyfuncs.c - copying a node
equalfuncs.c - comparing a node
outfuncs.c - convert a node to ascii representation
readfuncs.c - convert ascii representation back to a node
makefuncs.c - creator functions for primitive nodes
Node definitions:
nodes.h - define node tags (NodeTag)
pg_list.h - generic list
primnodes.h - primitive nodes
parsenodes.h - parse tree nodes
plannodes.h - plan tree nodes
relation.h - inner plan tree nodes
execnodes.h - executor nodes
memnodes.h - memory nodes
STEPS TO ADD A NODE
Suppose you wana define a node Foo:
1. add a tag (T_Foo) to the enum NodeTag in nodes.h (You may have to
recompile the whole tree after doing this.)
2. add the structure definition to the appropriate ???nodes.h file. If you
intend to inherit from, say a Plan node, put Plan as the first field of
you 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)
HISTORICAL NOTE
Prior to the current simple C structure definitions, the Node structures
uses a pseudo-inheritance system which automatically generates creator and
accessor functions. Since every node inherits from LispValue, the whole thing
is 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