sampling.h

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/*-------------------------------------------------------------------------
 *
 * sampling.h
 *    definitions for sampling functions
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/sampling.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef SAMPLING_H
#define SAMPLING_H
 
#include "common/pg_prng.h"
#include "storage/block.h"      /* for typedef BlockNumber */
 
 
/* Random generator for sampling code */
extern void sampler_random_init_state(uint32 seed,
                                      pg_prng_state *randstate);
extern double sampler_random_fract(pg_prng_state *randstate);
 
/* Block sampling methods */
 
/* Data structure for Algorithm S from Knuth 3.4.2 */
typedef struct
{
    BlockNumber N;              /* number of blocks, known in advance */
    int         n;              /* desired sample size */
    BlockNumber t;              /* current block number */
    int         m;              /* blocks selected so far */
    pg_prng_state randstate;    /* random generator state */
} BlockSamplerData;
 
typedef BlockSamplerData *BlockSampler;
 
extern BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
                                     int samplesize, uint32 randseed);
extern bool BlockSampler_HasMore(BlockSampler bs);
extern BlockNumber BlockSampler_Next(BlockSampler bs);
 
/* Reservoir sampling methods */
 
typedef struct
{
    double      W;
    pg_prng_state randstate;    /* random generator state */
} ReservoirStateData;
 
typedef ReservoirStateData *ReservoirState;
 
extern void reservoir_init_selection_state(ReservoirState rs, int n);
extern double reservoir_get_next_S(ReservoirState rs, double t, int n);
 
/* Old API, still in use by assorted FDWs */
/* For backwards compatibility, these declarations are duplicated in vacuum.h */
 
extern double anl_random_fract(void);
extern double anl_init_selection_state(int n);
extern double anl_get_next_S(double t, int n, double *stateptr);
 
#endif                          /* SAMPLING_H */