PostgreSQL Source Code: src/include/utils/sampling.h Source File

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sampling.h
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1/*-------------------------------------------------------------------------
2 *
3 * sampling.h
4 * definitions for sampling functions
5 *
6 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 * src/include/utils/sampling.h
10 *
11 *-------------------------------------------------------------------------
12 */
13#ifndef SAMPLING_H
14#define SAMPLING_H
15
16#include "common/pg_prng.h"
17#include "storage/block.h" /* for typedef BlockNumber */
18
19
20/* Random generator for sampling code */
21extern void sampler_random_init_state(uint32 seed,
22 pg_prng_state *randstate);
23extern double sampler_random_fract(pg_prng_state *randstate);
24
25/* Block sampling methods */
26
27/* Data structure for Algorithm S from Knuth 3.4.2 */
28 typedef struct
29{
30 BlockNumber N; /* number of blocks, known in advance */
31 int n; /* desired sample size */
32 BlockNumber t; /* current block number */
33 int m; /* blocks selected so far */
34 pg_prng_state randstate; /* random generator state */
35} BlockSamplerData;
36
37 typedef BlockSamplerData *BlockSampler;
38
39extern BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
40 int samplesize, uint32 randseed);
41extern bool BlockSampler_HasMore(BlockSampler bs);
42extern BlockNumber BlockSampler_Next(BlockSampler bs);
43
44/* Reservoir sampling methods */
45
46 typedef struct
47{
48 double W;
49 pg_prng_state randstate; /* random generator state */
50} ReservoirStateData;
51
52 typedef ReservoirStateData *ReservoirState;
53
54extern void reservoir_init_selection_state(ReservoirState rs, int n);
55extern double reservoir_get_next_S(ReservoirState rs, double t, int n);
56
57/* Old API, still in use by assorted FDWs */
58/* For backwards compatibility, these declarations are duplicated in vacuum.h */
59
60extern double anl_random_fract(void);
61extern double anl_init_selection_state(int n);
62extern double anl_get_next_S(double t, int n, double *stateptr);
63
64#endif /* SAMPLING_H */
uint32 BlockNumber
Definition: block.h:31
uint32_t uint32
Definition: c.h:538
BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks, int samplesize, uint32 randseed)
Definition: sampling.c:39
void reservoir_init_selection_state(ReservoirState rs, int n)
Definition: sampling.c:133
double anl_get_next_S(double t, int n, double *stateptr)
Definition: sampling.c:296
double sampler_random_fract(pg_prng_state *randstate)
Definition: sampling.c:241
bool BlockSampler_HasMore(BlockSampler bs)
Definition: sampling.c:58
ReservoirStateData * ReservoirState
Definition: sampling.h:52
BlockNumber BlockSampler_Next(BlockSampler bs)
Definition: sampling.c:64
double anl_init_selection_state(int n)
Definition: sampling.c:281
void sampler_random_init_state(uint32 seed, pg_prng_state *randstate)
Definition: sampling.c:234
BlockSamplerData * BlockSampler
Definition: sampling.h:37
double anl_random_fract(void)
Definition: sampling.c:266
double reservoir_get_next_S(ReservoirState rs, double t, int n)
Definition: sampling.c:147
BlockNumber N
Definition: sampling.h:30
pg_prng_state randstate
Definition: sampling.h:34
BlockNumber t
Definition: sampling.h:32
pg_prng_state randstate
Definition: sampling.h:49
Definition: pg_prng.h:20

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