fix-missing-value-corruption.patch

diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c
index cb2291ee36..acd801a07c 100644
--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -60,9 +60,12 @@
 #include "access/heaptoast.h"
 #include "access/sysattr.h"
 #include "access/tupdesc_details.h"
+#include "common/hashfn.h"
 #include "executor/tuptable.h"
+#include "utils/datum.h"
 #include "utils/expandeddatum.h"
-
+#include "utils/hsearch.h"
+#include "utils/memutils.h"
 
 /* Does att's datatype allow packing into the 1-byte-header varlena format? */
 #define ATT_IS_PACKABLE(att) \
@@ -71,6 +74,68 @@
 #define VARLENA_ATT_IS_PACKABLE(att) \
 	((att)->attstorage != TYPSTORAGE_PLAIN)
 
+/*
+ * Setup for cacheing pass-by-ref missing attributes in a way that survives
+ * tupleDesc destruction.
+ */
+
+typedef struct
+{
+	int			len;
+	Datum		value;
+} missing_cache_key;
+
+static HTAB *missing_cache = NULL;
+
+static uint32
+missing_hash(const void *key, Size keysize)
+{
+	const missing_cache_key *entry = (missing_cache_key *) key;
+
+	return hash_bytes((const unsigned char *) entry->value, entry->len);
+}
+
+static int
+missing_match(const void *key1, const void *key2, Size keysize)
+{
+	const missing_cache_key *entry1 = (missing_cache_key *) key1;
+	const missing_cache_key *entry2 = (missing_cache_key *) key2;
+
+	if (entry1->len != entry2->len)
+		return entry1->len > entry2->len ? 1 : -1;
+
+	return memcmp(DatumGetPointer(entry1->value),
+				  DatumGetPointer(entry2->value),
+				  entry1->len);
+}
+
+static void
+init_missing_cache()
+{
+	HASHCTL		hash_ctl;
+
+	hash_ctl.keysize = sizeof(missing_cache_key);
+	hash_ctl.entrysize = sizeof(missing_cache_key);
+	hash_ctl.hcxt = TopTransactionContext;
+	hash_ctl.hash = missing_hash;
+	hash_ctl.match = missing_match;
+	missing_cache =
+		hash_create("Missing Values Cache",
+					32,
+					&hash_ctl,
+					HASH_ELEM | HASH_CONTEXT | HASH_FUNCTION | HASH_COMPARE);
+}
+
+/* end of transaction routine to clear the missing values cache */
+void
+AtEOXact_MissCache(void)
+{
+	/*
+	 * just set the cache pointer to NULL, the context cleanup will do the
+	 * rest
+	 */
+	missing_cache = NULL;
+}
 
 /* ----------------------------------------------------------------
  *						misc support routines
@@ -102,8 +167,44 @@ getmissingattr(TupleDesc tupleDesc,
 
 		if (attrmiss->am_present)
 		{
+			missing_cache_key key;
+			missing_cache_key *entry;
+			bool		found;
+			MemoryContext oldctx;
+			Datum		copy;
+
 			*isnull = false;
-			return attrmiss->am_value;
+
+			/* no  need to cache by-value attributes */
+			if (att->attbyval)
+				return attrmiss->am_value;
+
+			/* set up cache if required */
+			if (missing_cache == NULL)
+				init_missing_cache();
+
+			/* check if there's a cache entry */
+			Assert(att->attlen > 0 || att->attlen == -1);
+			if (att->attlen > 0)
+				key.len = att->attlen;
+			else
+				key.len = VARSIZE_ANY(attrmiss->am_value);
+			key.value = attrmiss->am_value;
+
+			entry = hash_search(missing_cache, &key, HASH_ENTER, &found);
+
+			/* cache hit, so return it */
+			if (found)
+				return entry->value;
+
+			/* cache miss, so we need a transaction-stable copy of the datum */
+			oldctx = MemoryContextSwitchTo(TopTransactionContext);
+			copy = datumCopy(attrmiss->am_value, false, att->attlen);
+			MemoryContextSwitchTo(oldctx);
+
+			entry->value = copy;
+
+			return copy;
 		}
 	}
 
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 8daaa535ed..b2946b955e 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -21,6 +21,7 @@
 #include <unistd.h>
 
 #include "access/commit_ts.h"
+#include "access/htup_details.h"
 #include "access/multixact.h"
 #include "access/parallel.h"
 #include "access/subtrans.h"
@@ -2362,6 +2363,7 @@ CommitTransaction(void)
 	AtEOXact_GUC(true, 1);
 	AtEOXact_SPI(true);
 	AtEOXact_Enum();
+	AtEOXact_MissCache();
 	AtEOXact_on_commit_actions(true);
 	AtEOXact_Namespace(true, is_parallel_worker);
 	AtEOXact_SMgr();
diff --git a/src/include/access/htup_details.h b/src/include/access/htup_details.h
index e01f4f35c8..027c4f5436 100644
--- a/src/include/access/htup_details.h
+++ b/src/include/access/htup_details.h
@@ -736,6 +736,7 @@ extern MinimalTuple minimal_tuple_from_heap_tuple(HeapTuple htup);
 extern size_t varsize_any(void *p);
 extern HeapTuple heap_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
 extern MinimalTuple minimal_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
+extern void AtEOXact_MissCache(void);
 
 #ifndef FRONTEND
 /*
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 260854747b..91d57159db 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -3471,6 +3471,7 @@ mbstr_verifier
 memoize_hash
 memoize_iterator
 metastring
+missing_cache_key
 mix_data_t
 mixedStruct
 mode_t