1/*-------------------------------------------------------------------------
4 * Mechanism for accessing buffered relation data with look-ahead
7 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
8 * Portions Copyright (c) 1994, Regents of the University of California
10 * src/include/storage/read_stream.h
12 *-------------------------------------------------------------------------
20/* Default tuning, reasonable for many users. */
21 #define READ_STREAM_DEFAULT 0x00
24 * I/O streams that are performing maintenance work on behalf of potentially
25 * many users, and thus should be governed by maintenance_io_concurrency
26 * instead of effective_io_concurrency. For example, VACUUM or CREATE INDEX.
28 #define READ_STREAM_MAINTENANCE 0x01
31 * We usually avoid issuing prefetch advice automatically when sequential
32 * access is detected, but this flag explicitly disables it, for cases that
33 * might not be correctly detected. Explicit advice is known to perform worse
34 * than letting the kernel (at least Linux) detect sequential access.
36 #define READ_STREAM_SEQUENTIAL 0x02
39 * We usually ramp up from smaller reads to larger ones, to support users who
40 * don't know if it's worth reading lots of buffers yet. This flag disables
41 * that, declaring ahead of time that we'll be reading all available buffers.
43 #define READ_STREAM_FULL 0x04
46 * Opt-in to using AIO batchmode.
48 * Submitting IO in larger batches can be more efficient than doing so
49 * one-by-one, particularly for many small reads. It does, however, require
50 * the ReadStreamBlockNumberCB callback to abide by the restrictions of AIO
51 * batching (c.f. pgaio_enter_batchmode()). Basically, the callback may not:
53 * a) block without first calling pgaio_submit_staged(), unless a
54 * to-be-waited-on lock cannot be part of a deadlock, e.g. because it is
55 * never held while waiting for IO.
57 * b) start another batch (without first exiting batchmode and re-entering
60 * As this requires care and is nontrivial in some cases, batching is only
61 * used with explicit opt-in.
64 #define READ_STREAM_USE_BATCHING 0x08
69/* for block_range_read_stream_cb */
76/* Callback that returns the next block number to read. */
78 void *callback_private_data,
79 void *per_buffer_data);
82 void *callback_private_data,
83 void *per_buffer_data);
89 void *callback_private_data,
90 size_t per_buffer_data_size);
97 char smgr_persistence,
100 void *callback_private_data,
101 size_t per_buffer_data_size);
105#endif /* READ_STREAM_H */
ReadStream * read_stream_begin_smgr_relation(int flags, BufferAccessStrategy strategy, SMgrRelation smgr, char smgr_persistence, ForkNumber forknum, ReadStreamBlockNumberCB callback, void *callback_private_data, size_t per_buffer_data_size)
BlockNumber read_stream_next_block(ReadStream *stream, BufferAccessStrategy *strategy)
void read_stream_reset(ReadStream *stream)
Buffer read_stream_next_buffer(ReadStream *stream, void **per_buffer_data)
ReadStream * read_stream_begin_relation(int flags, BufferAccessStrategy strategy, Relation rel, ForkNumber forknum, ReadStreamBlockNumberCB callback, void *callback_private_data, size_t per_buffer_data_size)
void read_stream_end(ReadStream *stream)
BlockNumber(* ReadStreamBlockNumberCB)(ReadStream *stream, void *callback_private_data, void *per_buffer_data)
BlockNumber block_range_read_stream_cb(ReadStream *stream, void *callback_private_data, void *per_buffer_data)
struct BlockRangeReadStreamPrivate BlockRangeReadStreamPrivate
BlockNumber last_exclusive
BlockNumber current_blocknum
static void callback(struct sockaddr *addr, struct sockaddr *mask, void *unused)