src/include/utils/sampling.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * sampling.h
   4  *        definitions for sampling functions
   5  *
   6  * Portions Copyright (c) 1996-2022, 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 */
  21 extern void sampler_random_init_state(uint32 seed,
  22                                                                           pg_prng_state *randstate);
  23 extern 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
  39 extern BlockNumber BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
  40                                                                          int samplesize, uint32 randseed);
  41 extern bool BlockSampler_HasMore(BlockSampler bs);
  42 extern 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
  54 extern void reservoir_init_selection_state(ReservoirState rs, int n);
  55 extern 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
  60 extern double anl_random_fract(void);
  61 extern double anl_init_selection_state(int n);
  62 extern double anl_get_next_S(double t, int n, double *stateptr);
  63
  64 #endif                                                  /* SAMPLING_H */