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- /*-------------------------------------------------------------------------
- *
- * sampling.h
- * definitions for sampling functions
- *
- * Portions Copyright (c) 1996-2019, 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 */
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