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/*-------------------------------------------------------------------------
*
* read_stream.h
* Mechanism for accessing buffered relation data with look-ahead
*
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/read_stream.h
*
*-------------------------------------------------------------------------
*/
#ifndef READ_STREAM_H
#define READ_STREAM_H
#include "storage/bufmgr.h"
/* Default tuning, reasonable for many users. */
#define READ_STREAM_DEFAULT 0x00
/*
* I/O streams that are performing maintenance work on behalf of potentially
* many users, and thus should be governed by maintenance_io_concurrency
* instead of effective_io_concurrency. For example, VACUUM or CREATE INDEX.
*/
#define READ_STREAM_MAINTENANCE 0x01
/*
* We usually avoid issuing prefetch advice automatically when sequential
* access is detected, but this flag explicitly disables it, for cases that
* might not be correctly detected. Explicit advice is known to perform worse
* than letting the kernel (at least Linux) detect sequential access.
*/
#define READ_STREAM_SEQUENTIAL 0x02
/*
* We usually ramp up from smaller reads to larger ones, to support users who
* don't know if it's worth reading lots of buffers yet. This flag disables
* that, declaring ahead of time that we'll be reading all available buffers.
*/
#define READ_STREAM_FULL 0x04
struct ReadStream;
typedef struct ReadStream ReadStream;
/* Callback that returns the next block number to read. */
typedef BlockNumber (*ReadStreamBlockNumberCB) (ReadStream *stream,
void *callback_private_data,
void *per_buffer_data);
extern 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);
extern Buffer read_stream_next_buffer(ReadStream *stream, void **per_buffer_data);
extern void read_stream_reset(ReadStream *stream);
extern void read_stream_end(ReadStream *stream);
#endif /* READ_STREAM_H */
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