1/*-------------------------------------------------------------------------
4 * Dynamic shared memory areas.
6 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
10 * src/include/utils/dsa.h
12 *-------------------------------------------------------------------------
20/* The opaque type used for an area. */
25 * If this system only uses a 32-bit value for size_t, then use the 32-bit
26 * implementation of DSA. This limits the amount of DSA that can be created
27 * to something significantly less than the entire 4GB address space because
28 * the DSA pointer must encode both a segment identifier and an offset, but
29 * that shouldn't be a significant limitation in practice.
31 * If this system doesn't support atomic operations on 64-bit values, then
32 * we fall back to 32-bit dsa_pointer for lack of other options.
34 * For testing purposes, USE_SMALL_DSA_POINTER can be defined to force the use
35 * of 32-bit dsa_pointer even on systems capable of supporting a 64-bit
38#if SIZEOF_SIZE_T == 4 || !defined(PG_HAVE_ATOMIC_U64_SUPPORT) || \
39 defined(USE_SMALL_DSA_POINTER)
40#define SIZEOF_DSA_POINTER 4
42 #define SIZEOF_DSA_POINTER 8
46 * The type of 'relative pointers' to memory allocated by a dynamic shared
47 * area. dsa_pointer values can be shared with other processes, but must be
48 * converted to backend-local pointers before they can be dereferenced. See
49 * dsa_get_address. Also, an atomic version and appropriately sized atomic
52#if SIZEOF_DSA_POINTER == 4
55#define dsa_pointer_atomic_init pg_atomic_init_u32
56#define dsa_pointer_atomic_read pg_atomic_read_u32
57#define dsa_pointer_atomic_write pg_atomic_write_u32
58#define dsa_pointer_atomic_fetch_add pg_atomic_fetch_add_u32
59#define dsa_pointer_atomic_compare_exchange pg_atomic_compare_exchange_u32
60#define DSA_POINTER_FORMAT "%08x"
64 #define dsa_pointer_atomic_init pg_atomic_init_u64
65 #define dsa_pointer_atomic_read pg_atomic_read_u64
66 #define dsa_pointer_atomic_write pg_atomic_write_u64
67 #define dsa_pointer_atomic_fetch_add pg_atomic_fetch_add_u64
68 #define dsa_pointer_atomic_compare_exchange pg_atomic_compare_exchange_u64
69 #define DSA_POINTER_FORMAT "%016" PRIx64
72/* Flags for dsa_allocate_extended. */
73 #define DSA_ALLOC_HUGE 0x01 /* allow huge allocation (> 1 GB) */
74 #define DSA_ALLOC_NO_OOM 0x02 /* no failure if out-of-memory */
75 #define DSA_ALLOC_ZERO 0x04 /* zero allocated memory */
77/* A sentinel value for dsa_pointer used to indicate failure to allocate. */
78 #define InvalidDsaPointer ((dsa_pointer) 0)
81 * The number of bits used to represent the offset part of a dsa_pointer.
82 * This controls the maximum size of a segment, the maximum possible
83 * allocation size and also the maximum number of segments per area.
85#if SIZEOF_DSA_POINTER == 4
86#define DSA_OFFSET_WIDTH 27 /* 32 segments of size up to 128MB */
88 #define DSA_OFFSET_WIDTH 40 /* 1024 segments of size up to 1TB */
92 * The default size of the initial DSM segment that backs a dsa_area created
93 * by dsa_create. After creating some number of segments of the initial size
94 * we'll double this size, and so on. Larger segments may be created if
95 * necessary to satisfy large requests.
97 #define DSA_DEFAULT_INIT_SEGMENT_SIZE ((size_t) (1 * 1024 * 1024))
99/* The minimum size of a DSM segment. */
100 #define DSA_MIN_SEGMENT_SIZE ((size_t) (256 * 1024))
102/* The maximum size of a DSM segment. */
103 #define DSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
105/* Check if a dsa_pointer value is valid. */
106 #define DsaPointerIsValid(x) ((x) != InvalidDsaPointer)
108/* Allocate uninitialized memory with error on out-of-memory. */
109 #define dsa_allocate(area, size) \
110 dsa_allocate_extended(area, size, 0)
112/* Allocate zero-initialized memory with error on out-of-memory. */
113 #define dsa_allocate0(area, size) \
114 dsa_allocate_extended(area, size, DSA_ALLOC_ZERO)
116/* Create dsa_area with default segment sizes */
117 #define dsa_create(tranche_id) \
118 dsa_create_ext(tranche_id, DSA_DEFAULT_INIT_SEGMENT_SIZE, \
119 DSA_MAX_SEGMENT_SIZE)
121/* Create dsa_area with default segment sizes in an existing share memory space */
122 #define dsa_create_in_place(place, size, tranche_id, segment) \
123 dsa_create_in_place_ext(place, size, tranche_id, segment, \
124 DSA_DEFAULT_INIT_SEGMENT_SIZE, \
125 DSA_MAX_SEGMENT_SIZE)
128 * The type used for dsa_area handles. dsa_handle values can be shared with
129 * other processes, so that they can attach to them. This provides a way to
130 * share allocated storage with other processes.
132 * The handle for a dsa_area is currently implemented as the dsm_handle
133 * for the first DSM segment backing this dynamic storage area, but client
134 * code shouldn't assume that is true.
138/* Sentinel value to use for invalid dsa_handles. */
139 #define DSA_HANDLE_INVALID ((dsa_handle) DSM_HANDLE_INVALID)
142 size_t max_segment_size);
145 size_t init_segment_size,
146 size_t max_segment_size);
dsa_area * dsa_attach(dsa_handle handle)
void dsa_trim(dsa_area *area)
dsa_area * dsa_create_in_place_ext(void *place, size_t size, int tranche_id, dsm_segment *segment, size_t init_segment_size, size_t max_segment_size)
dsa_area * dsa_attach_in_place(void *place, dsm_segment *segment)
void * dsa_get_address(dsa_area *area, dsa_pointer dp)
dsa_pointer dsa_allocate_extended(dsa_area *area, size_t size, int flags)
size_t dsa_get_total_size(dsa_area *area)
void dsa_on_shmem_exit_release_in_place(int, Datum)
dsa_area * dsa_create_ext(int tranche_id, size_t init_segment_size, size_t max_segment_size)
void dsa_release_in_place(void *place)
void dsa_set_size_limit(dsa_area *area, size_t limit)
pg_atomic_uint64 dsa_pointer_atomic
void dsa_unpin(dsa_area *area)
void dsa_pin_mapping(dsa_area *area)
void dsa_dump(dsa_area *area)
void dsa_on_dsm_detach_release_in_place(dsm_segment *, Datum)
dsa_handle dsa_get_handle(dsa_area *area)
bool dsa_is_attached(dsa_handle handle)
void dsa_detach(dsa_area *area)
void dsa_free(dsa_area *area, dsa_pointer dp)
size_t dsa_minimum_size(void)
void dsa_pin(dsa_area *area)