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83e176ec18
Refactoring ahead of tablesample patch Requested and reviewed by Michael Paquier Petr Jelinek
45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
/*-------------------------------------------------------------------------
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*
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* sampling.h
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* definitions for sampling functions
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*
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* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/sampling.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SAMPLING_H
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#define SAMPLING_H
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#include "storage/bufmgr.h"
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extern double sampler_random_fract(void);
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/* Block sampling methods */
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/* Data structure for Algorithm S from Knuth 3.4.2 */
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typedef struct
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{
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BlockNumber N; /* number of blocks, known in advance */
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int n; /* desired sample size */
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BlockNumber t; /* current block number */
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int m; /* blocks selected so far */
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} BlockSamplerData;
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typedef BlockSamplerData *BlockSampler;
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extern void BlockSampler_Init(BlockSampler bs, BlockNumber nblocks,
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int samplesize, long randseed);
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extern bool BlockSampler_HasMore(BlockSampler bs);
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extern BlockNumber BlockSampler_Next(BlockSampler bs);
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/* Reservoid sampling methods */
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typedef double ReservoirStateData;
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typedef ReservoirStateData *ReservoirState;
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extern void reservoir_init_selection_state(ReservoirState rs, int n);
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extern double reservoir_get_next_S(ReservoirState rs, double t, int n);
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#endif /* SAMPLING_H */
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