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diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
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+/*-------------------------------------------------------------------------
+ *
+ * dshash.h
+ *	  Concurrent hash tables backed by dynamic shared memory areas.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/include/lib/dshash.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSHASH_H
+#define DSHASH_H
+
+#include "utils/dsa.h"
+
+/* The opaque type representing a hash table. */
+struct dshash_table;
+typedef struct dshash_table dshash_table;
+
+/* A handle for a dshash_table which can be shared with other processes. */
+typedef dsa_pointer dshash_table_handle;
+
+/* The type for hash values. */
+typedef uint32 dshash_hash;
+
+/* A function type for comparing keys. */
+typedef int (*dshash_compare_function) (const void *a, const void *b,
+										size_t size, void *arg);
+
+/* A function type for computing hash values for keys. */
+typedef dshash_hash (*dshash_hash_function) (const void *v, size_t size,
+											 void *arg);
+
+/*
+ * The set of parameters needed to create or attach to a hash table.  The
+ * members tranche_id and tranche_name do not need to be initialized when
+ * attaching to an existing hash table.
+ *
+ * Compare and hash functions must be supplied even when attaching, because we
+ * can't safely share function pointers between backends in general.  Either
+ * the arg variants or the non-arg variants should be supplied; the other
+ * function pointers should be NULL.  If the arg variants are supplied then the
+ * user data pointer supplied to the create and attach functions will be
+ * passed to the hash and compare functions.
+ */
+typedef struct dshash_parameters
+{
+	size_t		key_size;		/* Size of the key (initial bytes of entry) */
+	size_t		entry_size;		/* Total size of entry */
+	dshash_compare_function compare_function;	/* Compare function */
+	dshash_hash_function hash_function; /* Hash function */
+	int			tranche_id;		/* The tranche ID to use for locks */
+} dshash_parameters;
+
+/* Forward declaration of private types for use only by dshash.c. */
+struct dshash_table_item;
+typedef struct dshash_table_item dshash_table_item;
+
+/* Creating, sharing and destroying from hash tables. */
+extern dshash_table *dshash_create(dsa_area *area,
+								   const dshash_parameters *params,
+								   void *arg);
+extern dshash_table *dshash_attach(dsa_area *area,
+								   const dshash_parameters *params,
+								   dshash_table_handle handle,
+								   void *arg);
+extern void dshash_detach(dshash_table *hash_table);
+extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table);
+extern void dshash_destroy(dshash_table *hash_table);
+
+/* Finding, creating, deleting entries. */
+extern void *dshash_find(dshash_table *hash_table,
+						 const void *key, bool exclusive);
+extern void *dshash_find_or_insert(dshash_table *hash_table,
+								   const void *key, bool *found);
+extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
+extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
+extern void dshash_release_lock(dshash_table *hash_table, void *entry);
+
+/* Convenience hash and compare functions wrapping memcmp and tag_hash. */
+extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
+extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
+
+/* Debugging support. */
+extern void dshash_dump(dshash_table *hash_table);
+
+#endif							/* DSHASH_H */