granicus.if.org Git - postgresql/blob - src/include/utils/sampling.h

   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 */
  20 typedef unsigned short SamplerRandomState[3];
  21
  22 extern void sampler_random_init_state(long seed,
  23                                                   SamplerRandomState randstate);
  24 extern double sampler_random_fract(SamplerRandomState randstate);
  25
  26 /* Block sampling methods */
  27
  28 /* Data structure for Algorithm S from Knuth 3.4.2 */
  29 typedef 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
  38 typedef BlockSamplerData *BlockSampler;
  39
  40 extern void BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
  41                                   int samplesize, long randseed);
  42 extern bool BlockSampler_HasMore(BlockSampler bs);
  43 extern BlockNumber BlockSampler_Next(BlockSampler bs);
  44
  45 /* Reservoir sampling methods */
  46
  47 typedef struct
  48 {
  49         double          W;
  50         SamplerRandomState randstate;   /* random generator state */
  51 } ReservoirStateData;
  52
  53 typedef ReservoirStateData *ReservoirState;
  54
  55 extern void reservoir_init_selection_state(ReservoirState rs, int n);
  56 extern 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
  61 extern double anl_random_fract(void);
  62 extern double anl_init_selection_state(int n);
  63 extern double anl_get_next_S(double t, int n, double *stateptr);
  64
  65 #endif                                                  /* SAMPLING_H */