From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 11 Oct 2007 21:28:20 +0000 (+0000)
Subject: Ensure that the result of evaluating a function during constant-expression
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=c28c421850a6aba48132f45ecd79ac060bf1eabe;p=users%2Fbernd%2Fpostgres.git

Ensure that the result of evaluating a function during constant-expression
simplification gets detoasted before it is incorporated into a Const node.
Otherwise, if an immutable function were to return a TOAST pointer (an
unlikely case, but it can be made to happen), we would end up with a plan
that depends on the continued existence of the out-of-line toast datum.
---

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index bca819ccaa..fe878e4837 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2506,9 +2506,20 @@ evaluate_expr(Expr *expr, Oid result_type)
 	/* Get back to outer memory context */
 	MemoryContextSwitchTo(oldcontext);
 
-	/* Must copy result out of sub-context used by expression eval */
+	/*
+	 * Must copy result out of sub-context used by expression eval.
+	 *
+	 * Also, if it's varlena, forcibly detoast it.  This protects us against
+	 * storing TOAST pointers into plans that might outlive the referenced
+	 * data.
+	 */
 	if (!const_is_null)
-		const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
+	{
+		if (resultTypLen == -1)
+			const_val = PointerGetDatum(PG_DETOAST_DATUM_COPY(const_val));
+		else
+			const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
+	}
 
 	/* Release all the junk we just created */
 	FreeExecutorState(estate);