1 files changed, 177 insertions, 0 deletions
diff --git a/src/backend/utils/cache/attoptcache.c b/src/backend/utils/cache/attoptcache.c
new file mode 100644
index 0000000..9e252a0
--- /dev/null
+++ b/src/backend/utils/cache/attoptcache.c
@@ -0,0 +1,177 @@
+/*-------------------------------------------------------------------------
+ *
+ * attoptcache.c
+ *	  Attribute options cache management.
+ *
+ * Attribute options are cached separately from the fixed-size portion of
+ * pg_attribute entries, which are handled by the relcache.
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/cache/attoptcache.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/reloptions.h"
+#include "utils/attoptcache.h"
+#include "utils/catcache.h"
+#include "utils/hsearch.h"
+#include "utils/inval.h"
+#include "utils/syscache.h"
+
+
+/* Hash table for information about each attribute's options */
+static HTAB *AttoptCacheHash = NULL;
+
+/* attrelid and attnum form the lookup key, and must appear first */
+typedef struct
+{
+	Oid			attrelid;
+	int			attnum;
+} AttoptCacheKey;
+
+typedef struct
+{
+	AttoptCacheKey key;			/* lookup key - must be first */
+	AttributeOpts *opts;		/* options, or NULL if none */
+} AttoptCacheEntry;
+
+
+/*
+ * InvalidateAttoptCacheCallback
+ *		Flush all cache entries when pg_attribute is updated.
+ *
+ * When pg_attribute is updated, we must flush the cache entry at least
+ * for that attribute.  Currently, we just flush them all.  Since attribute
+ * options are not currently used in performance-critical paths (such as
+ * query execution), this seems OK.
+ */
+static void
+InvalidateAttoptCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
+{
+	HASH_SEQ_STATUS status;
+	AttoptCacheEntry *attopt;
+
+	hash_seq_init(&status, AttoptCacheHash);
+	while ((attopt = (AttoptCacheEntry *) hash_seq_search(&status)) != NULL)
+	{
+		if (attopt->opts)
+			pfree(attopt->opts);
+		if (hash_search(AttoptCacheHash,
+						(void *) &attopt->key,
+						HASH_REMOVE,
+						NULL) == NULL)
+			elog(ERROR, "hash table corrupted");
+	}
+}
+
+/*
+ * InitializeAttoptCache
+ *		Initialize the attribute options cache.
+ */
+static void
+InitializeAttoptCache(void)
+{
+	HASHCTL		ctl;
+
+	/* Initialize the hash table. */
+	ctl.keysize = sizeof(AttoptCacheKey);
+	ctl.entrysize = sizeof(AttoptCacheEntry);
+	AttoptCacheHash =
+		hash_create("Attopt cache", 256, &ctl,
+					HASH_ELEM | HASH_BLOBS);
+
+	/* Make sure we've initialized CacheMemoryContext. */
+	if (!CacheMemoryContext)
+		CreateCacheMemoryContext();
+
+	/* Watch for invalidation events. */
+	CacheRegisterSyscacheCallback(ATTNUM,
+								  InvalidateAttoptCacheCallback,
+								  (Datum) 0);
+}
+
+/*
+ * get_attribute_options
+ *		Fetch attribute options for a specified table OID.
+ */
+AttributeOpts *
+get_attribute_options(Oid attrelid, int attnum)
+{
+	AttoptCacheKey key;
+	AttoptCacheEntry *attopt;
+	AttributeOpts *result;
+	HeapTuple	tp;
+
+	/* Find existing cache entry, if any. */
+	if (!AttoptCacheHash)
+		InitializeAttoptCache();
+	memset(&key, 0, sizeof(key));	/* make sure any padding bits are unset */
+	key.attrelid = attrelid;
+	key.attnum = attnum;
+	attopt =
+		(AttoptCacheEntry *) hash_search(AttoptCacheHash,
+										 (void *) &key,
+										 HASH_FIND,
+										 NULL);
+
+	/* Not found in Attopt cache.  Construct new cache entry. */
+	if (!attopt)
+	{
+		AttributeOpts *opts;
+
+		tp = SearchSysCache2(ATTNUM,
+							 ObjectIdGetDatum(attrelid),
+							 Int16GetDatum(attnum));
+
+		/*
+		 * If we don't find a valid HeapTuple, it must mean someone has
+		 * managed to request attribute details for a non-existent attribute.
+		 * We treat that case as if no options were specified.
+		 */
+		if (!HeapTupleIsValid(tp))
+			opts = NULL;
+		else
+		{
+			Datum		datum;
+			bool		isNull;
+
+			datum = SysCacheGetAttr(ATTNUM,
+									tp,
+									Anum_pg_attribute_attoptions,
+									&isNull);
+			if (isNull)
+				opts = NULL;
+			else
+			{
+				bytea	   *bytea_opts = attribute_reloptions(datum, false);
+
+				opts = MemoryContextAlloc(CacheMemoryContext,
+										  VARSIZE(bytea_opts));
+				memcpy(opts, bytea_opts, VARSIZE(bytea_opts));
+			}
+			ReleaseSysCache(tp);
+		}
+
+		/*
+		 * It's important to create the actual cache entry only after reading
+		 * pg_attribute, since the read could cause a cache flush.
+		 */
+		attopt = (AttoptCacheEntry *) hash_search(AttoptCacheHash,
+												  (void *) &key,
+												  HASH_ENTER,
+												  NULL);
+		attopt->opts = opts;
+	}
+
+	/* Return results in caller's memory context. */
+	if (attopt->opts == NULL)
+		return NULL;
+	result = palloc(VARSIZE(attopt->opts));
+	memcpy(result, attopt->opts, VARSIZE(attopt->opts));
+	return result;
+}