The planner previously assumed that parameter Vars having the same absolute
query level, varno, and varattno could safely be assigned the same runtime
PARAM_EXEC slot, even though they might be different Vars appearing in
different subqueries. This was (probably) safe before the introduction of
CTEs, but the lazy-evalution mechanism used for CTEs means that a CTE can
be executed during execution of some other subquery, causing the lifespan
of Params at the same syntactic nesting level as the CTE to overlap with
use of the same slots inside the CTE. In 9.1 we created additional hazards
by using the same parameter-assignment technology for nestloop inner scan
parameters, but it was broken before that, as illustrated by the added
regression test.
To fix, restructure the planner's management of PlannerParamItems so that
items having different semantic lifespans are kept rigorously separated.
This will probably result in complex queries using more runtime PARAM_EXEC
slots than before, but the slots are cheap enough that this hardly matters.
Also, stop generating PlannerParamItems containing Params for subquery
outputs: all we really need to do is reserve the PARAM_EXEC slot number,
and that now only takes incrementing a counter. The planning code is
simpler and probably faster than before, as well as being more correct.
Per report from Vik Reykja.
These changes will mostly also need to be made in the back branches, but
I'm going to hold off on that until after 9.2.0 wraps.
This reduces unnecessary exposure of other headers through htup.h, which
is very widely included by many files.
I have chosen to move the function prototypes to the new file as well,
because that means htup.h no longer needs to include tupdesc.h. In
itself this doesn't have much effect in indirect inclusion of tupdesc.h
throughout the tree, because it's also required by execnodes.h; but it's
something to explore in the future, and it seemed best to do the htup.h
change now while I'm busy with it.
The heapam XLog functions are used by other modules, not all of which
are interested in the rest of the heapam API. With this, we let them
get just the XLog stuff in which they are interested and not pollute
them with unrelated includes.
Also, since heapam.h no longer requires xlog.h, many files that do
include heapam.h no longer get xlog.h automatically, including a few
headers. This is useful because heapam.h is getting pulled in by
execnodes.h, which is in turn included by a lot of files.
This patch takes care of a number of problems having to do with failure
to choose valid join orders and incorrect handling of lateral references
pulled up from subqueries. Notable changes:
* Add a LateralJoinInfo data structure similar to SpecialJoinInfo, to
represent join ordering constraints created by lateral references.
(I first considered extending the SpecialJoinInfo structure, but the
semantics are different enough that a separate data structure seems
better.) Extend join_is_legal() and related functions to prevent trying
to form unworkable joins, and to ensure that we will consider joins that
satisfy lateral references even if the joins would be clauseless.
* Fill in the infrastructure needed for the last few types of relation scan
paths to support parameterization. We'd have wanted this eventually
anyway, but it is necessary now because a relation that gets pulled up out
of a UNION ALL subquery may acquire a reltargetlist containing lateral
references, meaning that its paths *have* to be parameterized whether or
not we have any code that can push join quals down into the scan.
* Compute data about lateral references early in query_planner(), and save
in RelOptInfo nodes, to avoid repetitive calculations later.
* Assorted corner-case bug fixes.
There's probably still some bugs left, but this is a lot closer to being
real than it was before.
The latter was already the dominant use, and it's preferable because
in C the convention is that intXX means XX bits. Therefore, allowing
mixed use of int2, int4, int8, int16, int32 is obviously confusing.
Remove the typedefs for int2 and int4 for now. They don't seem to be
widely used outside of the PostgreSQL source tree, and the few uses
can probably be cleaned up by the time this ships.
This patch adjusts the treatment of parameterized paths so that all paths
with the same parameterization (same set of required outer rels) for the
same relation will have the same rowcount estimate. We cache the rowcount
estimates to ensure that property, and hopefully save a few cycles too.
Doing this makes it practical for add_path_precheck to operate without
a rowcount estimate: it need only assume that paths with different
parameterizations never dominate each other, which is close enough to
true anyway for coarse filtering, because normally a more-parameterized
path should yield fewer rows thanks to having more join clauses to apply.
In add_path, we do the full nine yards of comparing rowcount estimates
along with everything else, so that we can discard parameterized paths that
don't actually have an advantage. This fixes some issues I'd found with
add_path rejecting parameterized paths on the grounds that they were more
expensive than not-parameterized ones, even though they yielded many fewer
rows and hence would be cheaper once subsequent joining was considered.
To make the same-rowcounts assumption valid, we have to require that any
parameterized path enforce *all* join clauses that could be obtained from
the particular set of outer rels, even if not all of them are useful for
indexing. This is required at both base scans and joins. It's a good
thing anyway since the net impact is that join quals are checked at the
lowest practical level in the join tree. Hence, discard the original
rather ad-hoc mechanism for choosing parameterization joinquals, and build
a better one that has a more principled rule for when clauses can be moved.
The original rule was actually buggy anyway for lack of knowledge about
which relations are part of an outer join's outer side; getting this right
requires adding an outer_relids field to RestrictInfo.
The hstore and json datatypes both have record-conversion functions that
pay attention to column names in the composite values they're handed.
We used to not worry about inserting correct field names into tuple
descriptors generated at runtime, but given these examples it seems
useful to do so. Observe the nicer-looking results in the regression
tests whose results changed.
catversion bump because there is a subtle change in requirements for stored
rule parsetrees: RowExprs from ROW() constructs now have to include field
names.
Andrew Dunstan and Tom Lane
Formerly, set_subquery_pathlist and other creators of plans for subqueries
saved only the rangetable and rowMarks lists from the lower-level
PlannerInfo. But there's no reason not to remember the whole PlannerInfo,
and indeed this turns out to simplify matters in a number of places.
The immediate reason for doing this was so that the subroot will still be
accessible when we're trying to extract column statistics out of an
already-planned subquery. But now that I've done it, it seems like a good
code-beautification effort in its own right.
I also chose to get rid of the transient subrtable and subrowmark fields in
SubqueryScan nodes, in favor of having setrefs.c look up the subquery's
RelOptInfo. That required changing all the APIs in setrefs.c to pass
PlannerInfo not PlannerGlobal, which was a large but quite mechanical
transformation.
One side-effect not foreseen at the beginning is that this finally broke
inheritance_planner's assumption that replanning the same subquery RTE N
times would necessarily give interchangeable results each time. That
assumption was always pretty risky, but now we really have to make a
separate RTE for each instance so that there's a place to carry the
separate subroots.
The previous coding failed to account properly for the costs of evaluating
the input expressions of aggregates and window functions, as seen in a
recent gripe from Claudio Freire. (I said at the time that it wasn't
counting these costs at all; but on closer inspection, it was effectively
charging these costs once per output tuple. That is completely wrong for
aggregates, and not exactly right for window functions either.)
There was also a hard-wired assumption that aggregates and window functions
had procost 1.0, which is now fixed to respect the actual cataloged costs.
The costing of WindowAgg is still pretty bogus, since it doesn't try to
estimate the effects of spilling data to disk, but that seems like a
separate issue.
This area was a few bricks shy of a load, and badly under-commented too.
We have to ensure that the generated targetlist entries for a set-operation
node expose the correct collation for each entry, since higher-level
processing expects the tlist to reflect the true ordering of the plan's
output.
This hackery wouldn't be necessary if SortGroupClause carried collation
info ... but making it do so would inject more pain in the parser than
would be saved here. Still, we might want to rethink that sometime.
In nearly all cases, the caller already knows the correct collation, and
in a number of places, the value the caller has handy is more correct than
the default for the type would be. (In particular, this patch makes it
significantly less likely that eval_const_expressions will result in
changing the exposed collation of an expression.) So an internal lookup
is both expensive and wrong.
Flattening of subquery range tables during setrefs.c could lead to the
rangetable indexes in PlanRowMark nodes not matching up with the column
names previously assigned to the corresponding resjunk ctid (resp. tableoid
or wholerow) columns. Typical symptom would be either a "cannot extract
system attribute from virtual tuple" error or an Assert failure. This
wasn't a problem before 9.0 because we didn't support FOR UPDATE below the
top query level, and so the final flattening could never renumber an RTE
that was relevant to FOR UPDATE. Fix by using a plan-tree-wide unique
number for each PlanRowMark to label the associated resjunk columns, so
that the number need not change during flattening.
Per report from David Johnston (though I'm darned if I can see how this got
past initial testing of the relevant code). Back-patch to 9.0.
This adds collation support for columns and domains, a COLLATE clause
to override it per expression, and B-tree index support.
Peter Eisentraut
reviewed by Pavel Stehule, Itagaki Takahiro, Robert Haas, Noah Misch
In an inherited UPDATE/DELETE, each target table has its own subplan,
because it might have a column set different from other targets. This
means that the resjunk columns we add to support EvalPlanQual might be
at different physical column numbers in each subplan. The EvalPlanQual
rewrite I did for 9.0 failed to account for this, resulting in possible
misbehavior or even crashes during concurrent updates to the same row,
as seen in a recent report from Gordon Shannon. Revise the data structure
so that we track resjunk column numbers separately for each subplan.
I also chose to move responsibility for identifying the physical column
numbers back to executor startup, instead of assuming that numbers derived
during preprocess_targetlist would stay valid throughout subsequent
massaging of the plan. That's a bit slower, so we might want to consider
undoing it someday; but it would complicate the patch considerably and
didn't seem justifiable in a bug fix that has to be back-patched to 9.0.
Per my recent proposal, get rid of all the direct inspection of indexes
and manual generation of paths in planagg.c. Instead, set up
EquivalenceClasses for the aggregate argument expressions, and let the
regular path generation logic deal with creating paths that can satisfy
those sort orders. This makes planagg.c a bit more visible to the rest
of the planner than it was originally, but the approach is basically a lot
cleaner than before. A major advantage of doing it this way is that we get
MIN/MAX optimization on inheritance trees (using MergeAppend of indexscans)
practically for free, whereas in the old way we'd have had to add a whole
lot more duplicative logic.
One small disadvantage of this approach is that MIN/MAX aggregates can no
longer exploit partial indexes having an "x IS NOT NULL" predicate, unless
that restriction or something that implies it is specified in the query.
The previous implementation was able to use the added "x IS NOT NULL"
condition as an extra predicate proof condition, but in this version we
rely entirely on indexes that are considered usable by the main planning
process. That seems a fair tradeoff for the simplicity and functionality
gained.
Now that we're expecting a mergeclause's left_ec/right_ec to persist from
the initial assignments, we can't just blithely zero these out when
transforming such a clause in adjust_appendrel_attrs. But really it should
be okay to keep the parent's values, since a child table's derived Var
ought to be equivalent to the parent Var for all EquivalenceClass purposes.
(Indeed, I'm wondering whether we couldn't find a way to dispense with
add_child_rel_equivalences altogether. But this is wrong in any case.)
When a column is renamed, we recursively rename the same column in
all descendent tables. But if one of those tables also inherits that
column from a table outside the inheritance hierarchy rooted at the
named table, we must throw an error. The previous coding correctly
prohibited the rename when the parent had inherited the column from
elsewhere, but overlooked the case where the parent was OK but a child
table also inherited the same column from a second, unrelated parent.
For now, not backpatched due to lack of complaints from the field.
KaiGai Kohei, with further changes by me.
Reviewed by Bernd Helme and Tom Lane.
a lot of strange behaviors that occurred in join cases. We now identify the
"current" row for every joined relation in UPDATE, DELETE, and SELECT FOR
UPDATE/SHARE queries. If an EvalPlanQual recheck is necessary, we jam the
appropriate row into each scan node in the rechecking plan, forcing it to emit
only that one row. The former behavior could rescan the whole of each joined
relation for each recheck, which was terrible for performance, and what's much
worse could result in duplicated output tuples.
Also, the original implementation of EvalPlanQual could not re-use the recheck
execution tree --- it had to go through a full executor init and shutdown for
every row to be tested. To avoid this overhead, I've associated a special
runtime Param with each LockRows or ModifyTable plan node, and arranged to
make every scan node below such a node depend on that Param. Thus, by
signaling a change in that Param, the EPQ machinery can just rescan the
already-built test plan.
This patch also adds a prohibition on set-returning functions in the
targetlist of SELECT FOR UPDATE/SHARE. This is needed to avoid the
duplicate-output-tuple problem. It seems fairly reasonable since the
other restrictions on SELECT FOR UPDATE are meant to ensure that there
is a unique correspondence between source tuples and result tuples,
which an output SRF destroys as much as anything else does.
execMain.c and into a new plan node type LockRows. Like the recent change
to put table updating into a ModifyTable plan node, this increases planning
flexibility by allowing the operations to occur below the top level of the
plan tree. It's necessary in any case to restore the previous behavior of
having FOR UPDATE locking occur before ModifyTable does.
This partially refactors EvalPlanQual to allow multiple rows-under-test
to be inserted into the EPQ machinery before starting an EPQ test query.
That isn't sufficient to fix EPQ's general bogosity in the face of plans
that return multiple rows per test row, though. Since this patch is
mostly about getting some plan node infrastructure in place and not about
fixing ten-year-old bugs, I will leave EPQ improvements for another day.
Another behavioral change that we could now think about is doing FOR UPDATE
before LIMIT, but that too seems like it should be treated as a followon
patch.
They are now handled by a new plan node type called ModifyTable, which is
placed at the top of the plan tree. In itself this change doesn't do much,
except perhaps make the handling of RETURNING lists and inherited UPDATEs a
tad less klugy. But it is necessary preparation for the intended extension of
allowing RETURNING queries inside WITH.
Marko Tiikkaja
that's generated for a whole-row Var referencing the subquery, when the
subquery is in the nullable side of an outer join. The previous coding
instead put PlaceHolderVars around the elements of the RowExpr. The effect
was that when the outer join made the subquery outputs go to null, the
whole-row Var produced ROW(NULL,NULL,...) rather than just NULL. There
are arguments afoot about whether those things ought to be semantically
indistinguishable, but for the moment they are not entirely so, and the
planner needs to take care that its machinations preserve the difference.
Per bug #5025.
Making this feasible required refactoring ResolveNew() to allow more caller
control over what is substituted for a Var. I chose to make ResolveNew()
a wrapper around a new general-purpose function replace_rte_variables().
I also fixed the ancient bogosity that ResolveNew might fail to set
a query's hasSubLinks field after inserting a SubLink in it. Although
all current callers make sure that happens anyway, we've had bugs of that
sort before, and it seemed like a good time to install a proper solution.
Back-patch to 8.4. The problem can be demonstrated clear back to 8.0,
but the fix would be too invasive in earlier branches; not to mention
that people may be depending on the subtly-incorrect behavior. The
8.4 series is new enough that fixing this probably won't cause complaints,
but it might in older branches. Also, 8.4 shows the incorrect behavior
in more cases than older branches do, because it is able to flatten
subqueries in more cases.
I mistakenly removed it last month, thinking it was no longer needed ---
but it is still needed for dealing with joininfo lists. Fortunately this
bit of brain fade hadn't made it into any released versions yet.
substituting a child rel's output expressions into the appendrel's restriction
clauses yields a pseudoconstant restriction. We might be able to skip scanning
that child rel entirely (if we get constant FALSE), or generate a one-time
filter. 8.3 more or less accidentally generated plans that weren't completely
stupid in these cases, but that was only because an extra recursive level of
subquery_planner() always occurred and allowed const-simplification to happen.
8.4's ability to pull up appendrel members with non-Var outputs exposes the
fact that we need to work harder here. Per gripe from Sergey Burladyan.
ability to lock relations as they scan pg_inherits, and to ignore any
relations that have disappeared by the time we get lock on them. This
makes uses of these functions safe against concurrent DROP operations
on child tables: we will effectively ignore any just-dropped child,
rather than possibly throwing an error as in recent bug report from
Thomas Johansson (and similar past complaints). The behavior should
not change otherwise, since the code was acquiring those same locks
anyway, just a little bit later.
An exception is LockTableCommand(), which is still behaving unsafely;
but that seems to require some more discussion before we change it.
find_inheritance_children() and find_all_inheritors(). I got annoyed that
these are buried inside the planner but mostly used elsewhere. So, create
a new file catalog/pg_inherits.c and put them there, along with a couple
of other functions that search pg_inherits.
The code that modifies pg_inherits is (still) in tablecmds.c --- it's
kind of entangled with unrelated code that modifies pg_depend and other
stuff, so pulling it out seemed like a bigger change than I wanted to make
right now. But this file provides a natural home for it if anyone ever
gets around to that.
This commit just moves code around; it doesn't change anything, except
I succumbed to the temptation to make a couple of trivial optimizations
in typeInheritsFrom().
temp relations; this is no more expensive than before, now that we have
pg_class.relistemp. Insert tests into bufmgr.c to prevent attempting
to fetch pages from nonlocal temp relations. This provides a low-level
defense against bugs-of-omission allowing temp pages to be loaded into shared
buffers, as in the contrib/pgstattuple problem reported by Stuart Bishop.
While at it, tweak a bunch of places to use new relcache tests (instead of
expensive probes into pg_namespace) to detect local or nonlocal temp tables.
attribute numbering. Also, a parent whole-row reference should not require
select privilege on child columns that aren't inherited from the parent.
Problem diagnosed by KaiGai Kohei, though this isn't exactly his patch.
making pull_up_sublinks() construct a full-blown JoinExpr tree representation
of IN/EXISTS SubLinks that it is able to convert to semi or anti joins.
This makes pull_up_sublinks() a shade more complex, but the gain in semantic
clarity is worth it. I still have more to do in this area to address the
previously-discussed problems, but this commit in itself fixes at least one
bug in HEAD, as shown by added regression test case.
keys when considering a semi or anti join. This requires estimating the
selectivity of the merge qual as though it were a regular inner join condition.
To allow caching both that and the real outer-join-aware selectivity, split
RestrictInfo.this_selec into two fields.
This fixes one of the problems reported by Kevin Grittner.
return the tableoid as well as the ctid for any FOR UPDATE targets that
have child tables. All child tables are listed in the ExecRowMark list,
but the executor just skips the ones that didn't produce the current row.
Curiously, this longstanding restriction doesn't seem to have been documented
anywhere; so no doc changes.
we extended the appendrel mechanism to support UNION ALL optimization. The
reason nobody noticed was that we are not actually using attr_needed data for
appendrel children; hence it seems more reasonable to rip it out than fix it.
Back-patch to 8.2 because an Assert failure is possible in corner cases.
Per examination of an example from Jim Nasby.
In HEAD, also get rid of AppendRelInfo.col_mappings, which is quite inadequate
to represent UNION ALL situations; depend entirely on translated_vars instead.
until vars are distributed to rels during query_planner() startup. We don't
really need it before that, and not building it early has some advantages.
First, we don't need to put it through the various preprocessing steps, which
saves some cycles and eliminates the need for a number of routines to support
PlaceHolderInfo nodes at all. Second, this means one less unused plan for any
sub-SELECT appearing in a placeholder's expression, since we don't build
placeholder_list until after sublink expansion is complete.
