introducing new 'FastList' list-construction subroutines to use in
hot spots. This avoids the O(N^2) behavior of repeated lappend's
by keeping a tail pointer, while not changing behavior by reversing
list order as the lcons() method would do.
so that all executable expression nodes inherit from a common supertype
Expr. This is somewhat of an exercise in code purity rather than any
real functional advance, but getting rid of the extra Oper or Func node
formerly used in each operator or function call should provide at least
a little space and speed improvement.
initdb forced by changes in stored-rules representation.
returns-set boolean field in Func and Oper nodes. This allows cleaner,
more reliable tests for expressions returning sets in the planner and
parser. For example, a WHERE clause returning a set is now detected
and complained of in the parser, not only at runtime.
from Param nodes, per discussion a few days ago on pghackers. Add new
expression node type FieldSelect that implements the functionality where
it's actually needed. Clean up some other unused fields in Func nodes
as well.
NOTE: initdb forced due to change in stored expression trees for rules.
contained a sub-SELECT nested within an AND/OR tree that cnfify()
thought it should rearrange. Same physical sub-SELECT node could
end up linked into multiple places in resulting expression tree.
This is harmless for most node types, but not for SubLink.
Repair bug by making physical copies of subexpressions that get
logically duplicated by cnfify(). Also, tweak the heuristic that
decides whether it's a good idea to do cnfify() --- we don't really
want that to happen when it would cause multiple copies of a subselect
to be generated, I think.
2-Oct-98 or TODO.detail/cnfify) to decide whether we want to reduce
WHERE clause to CNF form, DNF form, or neither. This is a HUGE win.
The heuristic conditions could probably still use a little tweaking to
make sure we don't pick CNF when DNF would be better, or vice versa,
but the risk of exponential explosion in cnfify() is gone. I was able
to run ten-thousand-AND-subclause queries through the planner in a
reasonable amount of time.
conditions. There are some pretty bogus heuristics in prepqual.c that
try to decide whether to output CNF or DNF format; they need to be replaced,
likely. Right now the code is probably too willing to choose DNF form,
which might hurt performance in some cases that used to work OK.
But at least we have a foundation to build on.
in or_normalize, remove detection of duplicate subexpressions (since it's
highly unlikely to be worth the amount of time it takes), and introduce
a dnfify() entry point so that unintelligible backwards logic in UNION
processing can be eliminated. This is just an intermediate step ---
next thing is to look at not forcing the qual into CNF form when it would
be better off in DNF form.
space consumption in pull_args, and avoid doing the full CNF transform on
operands of operator clauses, where it's really not particularly helpful.
This answers the TODO item about large numbers of OR clauses, at least
partially. I was able to do a ten-thousand-OR-clause query with about
20Mb memory consumption ... it took an obscenely long time, but it worked...
Bruce Momjian
Tom Lane
Marc G. Fournier