1/*-------------------------------------------------------------------------
2 *
3 * sampling.h
4 * definitions for sampling functions
5 *
6 * Portions Copyright (c) 1996-2019, 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 "storage/block.h" /* for typedef BlockNumber */
17
18
19/* Random generator for sampling code */
20typedef unsigned short SamplerRandomState[3];
21
22extern void sampler_random_init_state(long seed,
23 SamplerRandomState randstate);
24extern double sampler_random_fract(SamplerRandomState randstate);
25
26/* Block sampling methods */
27
28/* Data structure for Algorithm S from Knuth 3.4.2 */
29typedef struct
30{
31 BlockNumber N; /* number of blocks, known in advance */
32 int n; /* desired sample size */
33 BlockNumber t; /* current block number */
34 int m; /* blocks selected so far */
35 SamplerRandomState randstate; /* random generator state */
36} BlockSamplerData;
37
38typedef BlockSamplerData *BlockSampler;
39
40extern void BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
41 int samplesize, long randseed);
42extern bool BlockSampler_HasMore(BlockSampler bs);
43extern BlockNumber BlockSampler_Next(BlockSampler bs);
44
45/* Reservoir sampling methods */
46
47typedef struct
48{
49 double W;
50 SamplerRandomState randstate; /* random generator state */
51} ReservoirStateData;
52
53typedef ReservoirStateData *ReservoirState;
54
55extern void reservoir_init_selection_state(ReservoirState rs, int n);
56extern double reservoir_get_next_S(ReservoirState rs, double t, int n);
57
58/* Old API, still in use by assorted FDWs */
59/* For backwards compatibility, these declarations are duplicated in vacuum.h */
60
61extern double anl_random_fract(void);
62extern double anl_init_selection_state(int n);
63extern double anl_get_next_S(double t, int n, double *stateptr);
64
65#endif /* SAMPLING_H */
66