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/*-------------------------------------------------------------------------
*
* sampling.h
* definitions for sampling functions
*
* Portions Copyright (c) 1996-2020, 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 "storage/block.h" /* for typedef BlockNumber */
/* Random generator for sampling code */
typedef unsigned short SamplerRandomState[3];
extern void sampler_random_init_state(long seed,
SamplerRandomState randstate);
extern double sampler_random_fract(SamplerRandomState 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 */
SamplerRandomState randstate; /* random generator state */
} BlockSamplerData;
typedef BlockSamplerData *BlockSampler;
extern BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
int samplesize, long randseed);
extern bool BlockSampler_HasMore(BlockSampler bs);
extern BlockNumber BlockSampler_Next(BlockSampler bs);
/* Reservoir sampling methods */
typedef struct
{
double W;
SamplerRandomState 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 */
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