sampling.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * sampling.h
 *    definitions for sampling functions
 *
 * Portions Copyright (c) 1996-2016, 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 void 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 */