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Fix handling of argument and result datatypes for partial aggregation.

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When doing partial aggregation, the args list of the upper (combining)
Aggref node is replaced by a Var representing the output of the partial
aggregation steps, which has either the aggregate's transition data type
or a serialized representation of that.  However, nodeAgg.c blindly
continued to use the args list as an indication of the user-level argument
types.  This broke resolution of polymorphic transition datatypes at
executor startup (though it accidentally failed to fail for the ANYARRAY
case, which is likely the only one anyone had tested).  Moreover, the
constructed FuncExpr passed to the finalfunc contained completely wrong
information, which would have led to bogus answers or crashes for any case
where the finalfunc examined that information (which is only likely to be
with polymorphic aggregates using a non-polymorphic transition type).

As an independent bug, apply_partialaggref_adjustment neglected to resolve
a polymorphic transition datatype before assigning it as the output type
of the lower-level Aggref node.  This again accidentally failed to fail
for ANYARRAY but would be unlikely to work in other cases.

To fix the first problem, record the user-level argument types in a
separate OID-list field of Aggref, and look to that rather than the args
list when asking what the argument types were.  (It turns out to be
convenient to include any "direct" arguments in this list too, although
those are not currently subject to being overwritten.)

Rather than adding yet another resolve_aggregate_transtype() call to fix
the second problem, add an aggtranstype field to Aggref, and store the
resolved transition type OID there when the planner first computes it.
(By doing this in the planner and not the parser, we can allow the
aggregate's transition type to change from time to time, although no DDL
support yet exists for that.)  This saves nothing of consequence for
simple non-polymorphic aggregates, but for polymorphic transition types
we save a catalog lookup during executor startup as well as several
planner lookups that are new in 9.6 due to parallel query planning.

In passing, fix an error that was introduced into count_agg_clauses_walker
some time ago: it was applying exprTypmod() to something that wasn't an
expression node at all, but a TargetEntry.  exprTypmod silently returned
-1 so that there was not an obvious failure, but this broke the intended
sensitivity of aggregate space consumption estimates to the typmod of
varchar and similar data types.  This part needs to be back-patched.

Catversion bump due to change of stored Aggref nodes.

Discussion: <8229.1466109074@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-06-17 21:44:37 -04:00
parent d30d1acf90
commit 915b703e16
13 changed files with 105 additions and 54 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
src/backend/optimizer/plan/setrefs.c
View File

@ -2085,6 +2085,7 @@ search_indexed_tlist_for_partial_aggref(Aggref *aggref, indexed_tlist *itlist,
continue;
if (aggref->inputcollid != tlistaggref->inputcollid)
continue;
/* ignore aggtranstype and aggargtypes, should be redundant */
if (!equal(aggref->aggdirectargs, tlistaggref->aggdirectargs))
continue;
if (!equal(aggref->args, tlistaggref->args))

54
src/backend/optimizer/util/clauses.c
View File

@ -523,7 +523,7 @@ contain_agg_clause_walker(Node *node, void *context)
/*
* count_agg_clauses
* Recursively count the Aggref nodes in an expression tree, and
* accumulate other cost information about them too.
* accumulate other information about them too.
*
* Note: this also checks for nested aggregates, which are an error.
*
@ -532,6 +532,10 @@ contain_agg_clause_walker(Node *node, void *context)
* values if all are evaluated in parallel (as would be done in a HashAgg
* plan). See AggClauseCosts for the exact set of statistics collected.
*
* In addition, we mark Aggref nodes with the correct aggtranstype, so
* that that doesn't need to be done repeatedly. (That makes this function's
* name a bit of a misnomer.)
*
* NOTE that the counts/costs are ADDED to those already in *costs ... so
* the caller is responsible for zeroing the struct initially.
*
@ -572,8 +576,6 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
Oid aggtranstype;
int32 aggtransspace;
QualCost argcosts;
Oid inputTypes[FUNC_MAX_ARGS];
int numArguments;
Assert(aggref->agglevelsup == 0);
@ -597,6 +599,28 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
aggtransspace = aggform->aggtransspace;
ReleaseSysCache(aggTuple);
/*
* Resolve the possibly-polymorphic aggregate transition type, unless
* already done in a previous pass over the expression.
*/
if (OidIsValid(aggref->aggtranstype))
aggtranstype = aggref->aggtranstype;
else
{
Oid inputTypes[FUNC_MAX_ARGS];
int numArguments;
/* extract argument types (ignoring any ORDER BY expressions) */
numArguments = get_aggregate_argtypes(aggref, inputTypes);
/* resolve actual type of transition state, if polymorphic */
aggtranstype = resolve_aggregate_transtype(aggref->aggfnoid,
aggtranstype,
inputTypes,
numArguments);
aggref->aggtranstype = aggtranstype;
}
/* count it; note ordered-set aggs always have nonempty aggorder */
costs->numAggs++;
if (aggref->aggorder != NIL || aggref->aggdistinct != NIL)
@ -668,15 +692,6 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
costs->finalCost += argcosts.per_tuple;
}
/* extract argument types (ignoring any ORDER BY expressions) */
numArguments = get_aggregate_argtypes(aggref, inputTypes);
/* resolve actual type of transition state, if polymorphic */
aggtranstype = resolve_aggregate_transtype(aggref->aggfnoid,
aggtranstype,
inputTypes,
numArguments);
/*
* If the transition type is pass-by-value then it doesn't add
* anything to the required size of the hashtable. If it is
@ -698,14 +713,15 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
* This works for cases like MAX/MIN and is probably somewhat
* reasonable otherwise.
*/
int numdirectargs = list_length(aggref->aggdirectargs);
int32 aggtranstypmod;
int32 aggtranstypmod = -1;
if (numArguments > numdirectargs &&
aggtranstype == inputTypes[numdirectargs])
aggtranstypmod = exprTypmod((Node *) linitial(aggref->args));
else
aggtranstypmod = -1;
if (aggref->args)
{
TargetEntry *tle = (TargetEntry *) linitial(aggref->args);
if (aggtranstype == exprType((Node *) tle->expr))
aggtranstypmod = exprTypmod((Node *) tle->expr);
}
avgwidth = get_typavgwidth(aggtranstype, aggtranstypmod);
}

13
src/backend/optimizer/util/tlist.c
View File

@ -797,11 +797,20 @@ apply_partialaggref_adjustment(PathTarget *target)
newaggref = (Aggref *) copyObject(aggref);
/* use the serialization type, if one exists */
/*
* Use the serialization type, if one exists. Note that we don't
* support it being a polymorphic type. (XXX really we ought to
* hardwire this as INTERNAL -> BYTEA, and avoid a catalog lookup
* here altogether?)
*/
if (OidIsValid(aggform->aggserialtype))
newaggref->aggoutputtype = aggform->aggserialtype;
else
newaggref->aggoutputtype = aggform->aggtranstype;
{
/* Otherwise, we return the aggregate's transition type */
Assert(OidIsValid(newaggref->aggtranstype));
newaggref->aggoutputtype = newaggref->aggtranstype;
}
/* flag it as partial */
newaggref->aggpartial = true;