From d2d9731291ab917df9b8e535ab54bd771be00e70 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Wed, 25 Jul 2012 10:21:40 -0400
Subject: [PATCH] Avoid leaking nodes on a failed insert.

---
 contrib/hashtest/hashtest.c    |  3 +++
 src/backend/utils/hash/chash.c | 27 ++++++++++++++++++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/contrib/hashtest/hashtest.c b/contrib/hashtest/hashtest.c
index 825f65e0cf..7c68e982a4 100644
--- a/contrib/hashtest/hashtest.c
+++ b/contrib/hashtest/hashtest.c
@@ -79,6 +79,9 @@ test_chash(PG_FUNCTION_ARGS)
 		ok = CHashInsert(chash, &e);
 		if (!ok)
 			elog(LOG, "insert %u: failed", i);
+		ok = CHashInsert(chash, &e);
+		if (ok)
+			elog(LOG, "insert %u: worked twice", i);
 	}
 
 	for (i = 0; i < 1000000; ++i)
diff --git a/src/backend/utils/hash/chash.c b/src/backend/utils/hash/chash.c
index 9053f44539..aa9005ca3a 100644
--- a/src/backend/utils/hash/chash.c
+++ b/src/backend/utils/hash/chash.c
@@ -185,6 +185,7 @@ typedef struct CHashTableData
 
 /* Function prototypes. */
 static CHashPtr CHashAllocate(CHashTable table);
+static void CHashImmediateFree(CHashTable table, CHashPtr c);
 static bool CHashRemoveMarked(CHashTable table, uint32 bucket,
 				  CHashPtr *cp, volatile CHashPtr *p);
 
@@ -548,9 +549,7 @@ retry:
 
 	/* If the insert failed, free the entry we allocated. */
 	if (found)
-	{
-		/* XXX Need some code here! */
-	}
+		CHashImmediateFree(table, new);
 
 	/* The insert succeeded if and only if no duplicate was found. */
 	return !found;
@@ -700,6 +699,28 @@ CHashAllocate(CHashTable table)
 	}
 }
 
+/*
+ * Free an arena slot immediately.
+ *
+ * When a slot that's actually in use is freed, we can't use this routine,
+ * because a concurrent bucket scan might have a private pointer to the
+ * object.  However, if an insert fails due to a duplicate key, then we need
+ * to put it back on the free list immediately.
+ */
+static void
+CHashImmediateFree(CHashTable table, CHashPtr c)
+{
+	volatile CHashTable vtable = table;
+	volatile CHashNode  *n;
+	uint32		f_home = ((uint32) MyBackendId) % table->nfreelists;
+
+	n = CHashTableGetNode(table, c);
+	SpinLockAcquire(&vtable->freelist[f_home].mutex);
+	n->un.gcnext = vtable->freelist[f_home].head;
+	vtable->freelist[f_home].head = c;
+	SpinLockRelease(&vtable->freelist[f_home].mutex);
+}
+
 /*
  * Attempt to remove marked elements from a bucket chain.
  *
-- 
2.39.5