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diff --git a/src/include/utils/dsa.h b/src/include/utils/dsa.h
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+/*-------------------------------------------------------------------------
+ *
+ * dsa.h
+ *	  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/utils/dsa.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSA_H
+#define DSA_H
+
+#include "port/atomics.h"
+#include "storage/dsm.h"
+
+/* The opaque type used for an area. */
+struct dsa_area;
+typedef struct dsa_area dsa_area;
+
+/*
+ * If this system only uses a 32-bit value for size_t, then use the 32-bit
+ * implementation of DSA.  This limits the amount of DSA that can be created
+ * to something significantly less than the entire 4GB address space because
+ * the DSA pointer must encode both a segment identifier and an offset, but
+ * that shouldn't be a significant limitation in practice.
+ *
+ * If this system doesn't support atomic operations on 64-bit values, then
+ * we fall back to 32-bit dsa_pointer for lack of other options.
+ *
+ * For testing purposes, USE_SMALL_DSA_POINTER can be defined to force the use
+ * of 32-bit dsa_pointer even on systems capable of supporting a 64-bit
+ * dsa_pointer.
+ */
+#if SIZEOF_SIZE_T == 4 || !defined(PG_HAVE_ATOMIC_U64_SUPPORT) || \
+	defined(USE_SMALL_DSA_POINTER)
+#define SIZEOF_DSA_POINTER 4
+#else
+#define SIZEOF_DSA_POINTER 8
+#endif
+
+/*
+ * The type of 'relative pointers' to memory allocated by a dynamic shared
+ * area.  dsa_pointer values can be shared with other processes, but must be
+ * converted to backend-local pointers before they can be dereferenced.  See
+ * dsa_get_address.  Also, an atomic version and appropriately sized atomic
+ * operations.
+ */
+#if SIZEOF_DSA_POINTER == 4
+typedef uint32 dsa_pointer;
+typedef pg_atomic_uint32 dsa_pointer_atomic;
+#define dsa_pointer_atomic_init pg_atomic_init_u32
+#define dsa_pointer_atomic_read pg_atomic_read_u32
+#define dsa_pointer_atomic_write pg_atomic_write_u32
+#define dsa_pointer_atomic_fetch_add pg_atomic_fetch_add_u32
+#define dsa_pointer_atomic_compare_exchange pg_atomic_compare_exchange_u32
+#define DSA_POINTER_FORMAT "%08x"
+#else
+typedef uint64 dsa_pointer;
+typedef pg_atomic_uint64 dsa_pointer_atomic;
+#define dsa_pointer_atomic_init pg_atomic_init_u64
+#define dsa_pointer_atomic_read pg_atomic_read_u64
+#define dsa_pointer_atomic_write pg_atomic_write_u64
+#define dsa_pointer_atomic_fetch_add pg_atomic_fetch_add_u64
+#define dsa_pointer_atomic_compare_exchange pg_atomic_compare_exchange_u64
+#define DSA_POINTER_FORMAT "%016" INT64_MODIFIER "x"
+#endif
+
+/* Flags for dsa_allocate_extended. */
+#define DSA_ALLOC_HUGE		0x01	/* allow huge allocation (> 1 GB) */
+#define DSA_ALLOC_NO_OOM	0x02	/* no failure if out-of-memory */
+#define DSA_ALLOC_ZERO		0x04	/* zero allocated memory */
+
+/* A sentinel value for dsa_pointer used to indicate failure to allocate. */
+#define InvalidDsaPointer ((dsa_pointer) 0)
+
+/* Check if a dsa_pointer value is valid. */
+#define DsaPointerIsValid(x) ((x) != InvalidDsaPointer)
+
+/* Allocate uninitialized memory with error on out-of-memory. */
+#define dsa_allocate(area, size) \
+	dsa_allocate_extended(area, size, 0)
+
+/* Allocate zero-initialized memory with error on out-of-memory. */
+#define dsa_allocate0(area, size) \
+	dsa_allocate_extended(area, size, DSA_ALLOC_ZERO)
+
+/*
+ * The type used for dsa_area handles.  dsa_handle values can be shared with
+ * other processes, so that they can attach to them.  This provides a way to
+ * share allocated storage with other processes.
+ *
+ * The handle for a dsa_area is currently implemented as the dsm_handle
+ * for the first DSM segment backing this dynamic storage area, but client
+ * code shouldn't assume that is true.
+ */
+typedef dsm_handle dsa_handle;
+
+extern dsa_area *dsa_create(int tranche_id);
+extern dsa_area *dsa_create_in_place(void *place, size_t size,
+									 int tranche_id, dsm_segment *segment);
+extern dsa_area *dsa_attach(dsa_handle handle);
+extern dsa_area *dsa_attach_in_place(void *place, dsm_segment *segment);
+extern void dsa_release_in_place(void *place);
+extern void dsa_on_dsm_detach_release_in_place(dsm_segment *, Datum);
+extern void dsa_on_shmem_exit_release_in_place(int, Datum);
+extern void dsa_pin_mapping(dsa_area *area);
+extern void dsa_detach(dsa_area *area);
+extern void dsa_pin(dsa_area *area);
+extern void dsa_unpin(dsa_area *area);
+extern void dsa_set_size_limit(dsa_area *area, size_t limit);
+extern size_t dsa_minimum_size(void);
+extern dsa_handle dsa_get_handle(dsa_area *area);
+extern dsa_pointer dsa_allocate_extended(dsa_area *area, size_t size, int flags);
+extern void dsa_free(dsa_area *area, dsa_pointer dp);
+extern void *dsa_get_address(dsa_area *area, dsa_pointer dp);
+extern void dsa_trim(dsa_area *area);
+extern void dsa_dump(dsa_area *area);
+
+#endif							/* DSA_H */