From 82480e28f5744582dba78320824e3569ed76e74a Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 20 Jun 2009 18:45:28 +0000
Subject: [PATCH] Fix things so that array_agg_finalfn does not modify or free
its input ArrayBuildState, per trouble report from Merlin Moncure. By
adopting this fix, we are essentially deciding that aggregate final-functions
should not modify their inputs ever. Adjust documentation and comments to
match that conclusion.
---
doc/src/sgml/xaggr.sgml | 10 +++++++---
src/backend/executor/nodeWindowAgg.c | 7 +++----
src/backend/utils/adt/array_userfuncs.c | 9 ++++++---
src/backend/utils/adt/arrayfuncs.c | 18 +++++++++++++++---
4 files changed, 31 insertions(+), 13 deletions(-)
diff --git a/doc/src/sgml/xaggr.sgml b/doc/src/sgml/xaggr.sgml
index b223888f9ed..1175b3640d7 100644
--- a/doc/src/sgml/xaggr.sgml
+++ b/doc/src/sgml/xaggr.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/xaggr.sgml,v 1.37 2008/12/28 18:53:54 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/xaggr.sgml,v 1.38 2009/06/20 18:45:28 tgl Exp $ -->
<sect1 id="xaggr">
<title>User-Defined Aggregates</title>
@@ -175,10 +175,14 @@ SELECT attrelid::regclass, array_accum(atttypid::regtype)
(IsA(fcinfo->context, AggState) ||
IsA(fcinfo->context, WindowAggState)))
</programlisting>
- One reason for checking this is that when it is true, the first input
+ One reason for checking this is that when it is true for a transition
+ function, the first input
must be a temporary transition value and can therefore safely be modified
in-place rather than allocating a new copy. (This is the <emphasis>only</>
- case where it is safe for a function to modify a pass-by-reference input.)
+ case where it is safe for a function to modify a pass-by-reference input.
+ In particular, aggregate final functions should not modify their inputs in
+ any case, because in some cases they will be re-executed on the same
+ final transition value.)
See <literal>int8inc()</> for an example.
</para>
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 0d9eb21a919..7343cb3752e 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -27,7 +27,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/executor/nodeWindowAgg.c,v 1.5 2009/06/11 14:48:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/executor/nodeWindowAgg.c,v 1.6 2009/06/20 18:45:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -410,9 +410,8 @@ eval_windowaggregates(WindowAggState *winstate)
* need the current aggregate value. This is considerably more efficient
* than the naive approach of re-running the entire aggregate calculation
* for each current row. It does assume that the final function doesn't
- * damage the running transition value. (Some C-coded aggregates do that
- * for efficiency's sake --- but they are supposed to do so only when
- * their fcinfo->context is an AggState, not a WindowAggState.)
+ * damage the running transition value, but we have the same assumption
+ * in nodeAgg.c too (when it rescans an existing hash table).
*
* In many common cases, multiple rows share the same frame and hence the
* same aggregate value. (In particular, if there's no ORDER BY in a RANGE
diff --git a/src/backend/utils/adt/array_userfuncs.c b/src/backend/utils/adt/array_userfuncs.c
index c30d6b42b07..a1f48d8784c 100644
--- a/src/backend/utils/adt/array_userfuncs.c
+++ b/src/backend/utils/adt/array_userfuncs.c
@@ -6,7 +6,7 @@
* Copyright (c) 2003-2009, PostgreSQL Global Development Group
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.30 2009/06/11 14:49:03 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/array_userfuncs.c,v 1.31 2009/06/20 18:45:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -537,10 +537,13 @@ array_agg_finalfn(PG_FUNCTION_ARGS)
dims[0] = state->nelems;
lbs[0] = 1;
- /* Release working state if regular aggregate, but not if window agg */
+ /*
+ * Make the result. We cannot release the ArrayBuildState because
+ * sometimes aggregate final functions are re-executed.
+ */
result = makeMdArrayResult(state, 1, dims, lbs,
CurrentMemoryContext,
- IsA(fcinfo->context, AggState));
+ false);
PG_RETURN_DATUM(result);
}
diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index b3973fbccb9..54c489a8969 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.157 2009/06/11 14:49:03 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/arrayfuncs.c,v 1.158 2009/06/20 18:45:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -4179,9 +4179,21 @@ accumArrayResult(ArrayBuildState *astate,
}
}
- /* Use datumCopy to ensure pass-by-ref stuff is copied into mcontext */
+ /*
+ * Ensure pass-by-ref stuff is copied into mcontext; and detoast it too
+ * if it's varlena. (You might think that detoasting is not needed here
+ * because construct_md_array can detoast the array elements later.
+ * However, we must not let construct_md_array modify the ArrayBuildState
+ * because that would mean array_agg_finalfn damages its input, which
+ * is verboten. Also, this way frequently saves one copying step.)
+ */
if (!disnull && !astate->typbyval)
- dvalue = datumCopy(dvalue, astate->typbyval, astate->typlen);
+ {
+ if (astate->typlen == -1)
+ dvalue = PointerGetDatum(PG_DETOAST_DATUM_COPY(dvalue));
+ else
+ dvalue = datumCopy(dvalue, astate->typbyval, astate->typlen);
+ }
astate->dvalues[astate->nelems] = dvalue;
astate->dnulls[astate->nelems] = disnull;
--
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