From db80acfc9d50ac56811d22802ab3d822ab313055 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Tue, 20 Dec 2016 09:20:17 +0200
Subject: [PATCH] Fix sharing Agg transition state of DISTINCT or ordered aggs.
If a query contained two aggregates that could share the transition value,
we would correctly collect the input into a tuplesort only once, but
incorrectly run the transition function over the accumulated input twice,
in finalize_aggregates(). That caused a crash, when we tried to call
tuplesort_performsort() on an already-freed NULL tuplestore.
Backport to 9.6, where sharing of transition state and this bug were
introduced.
Analysis by Tom Lane.
Discussion: https://www.postgresql.org/message-id/ac5b0b69-744c-9114-6218-8300ac920e61@iki.fi
---
src/backend/executor/nodeAgg.c | 21 ++++++++++++++++++---
src/test/regress/expected/aggregates.out | 9 +++++++++
src/test/regress/sql/aggregates.sql | 3 +++
3 files changed, 30 insertions(+), 3 deletions(-)
diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index a093862f34b..781938e2bb4 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -1575,16 +1575,19 @@ finalize_aggregates(AggState *aggstate,
Datum *aggvalues = econtext->ecxt_aggvalues;
bool *aggnulls = econtext->ecxt_aggnulls;
int aggno;
+ int transno;
Assert(currentSet == 0 ||
((Agg *) aggstate->ss.ps.plan)->aggstrategy != AGG_HASHED);
aggstate->current_set = currentSet;
- for (aggno = 0; aggno < aggstate->numaggs; aggno++)
+ /*
+ * If there were any DISTINCT and/or ORDER BY aggregates, sort their
+ * inputs and run the transition functions.
+ */
+ for (transno = 0; transno < aggstate->numtrans; transno++)
{
- AggStatePerAgg peragg = &peraggs[aggno];
- int transno = peragg->transno;
AggStatePerTrans pertrans = &aggstate->pertrans[transno];
AggStatePerGroup pergroupstate;
@@ -1603,6 +1606,18 @@ finalize_aggregates(AggState *aggstate,
pertrans,
pergroupstate);
}
+ }
+
+ /*
+ * Run the final functions.
+ */
+ for (aggno = 0; aggno < aggstate->numaggs; aggno++)
+ {
+ AggStatePerAgg peragg = &peraggs[aggno];
+ int transno = peragg->transno;
+ AggStatePerGroup pergroupstate;
+
+ pergroupstate = &pergroup[transno + (currentSet * (aggstate->numtrans))];
if (DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit))
finalize_partialaggregate(aggstate, peragg, pergroupstate,
diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index 45208a6da66..fa1f5e78798 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -1816,6 +1816,15 @@ NOTICE: avg_transfn called with 3
2 | 4
(1 row)
+-- same as previous one, but with DISTINCT, which requires sorting the input.
+select my_avg(distinct one),my_sum(distinct one) from (values(1),(3),(1)) t(one);
+NOTICE: avg_transfn called with 1
+NOTICE: avg_transfn called with 3
+ my_avg | my_sum
+--------+--------
+ 2 | 4
+(1 row)
+
-- shouldn't share states due to the distinctness not matching.
select my_avg(distinct one),my_sum(one) from (values(1),(3)) t(one);
NOTICE: avg_transfn called with 1
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index 430ac49385c..2eeb3eedbdf 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -727,6 +727,9 @@ select my_avg(one),my_avg(one) from (values(1),(3)) t(one);
-- aggregate state should be shared as transfn is the same for both aggs.
select my_avg(one),my_sum(one) from (values(1),(3)) t(one);
+-- same as previous one, but with DISTINCT, which requires sorting the input.
+select my_avg(distinct one),my_sum(distinct one) from (values(1),(3),(1)) t(one);
+
-- shouldn't share states due to the distinctness not matching.
select my_avg(distinct one),my_sum(one) from (values(1),(3)) t(one);
--
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