From 83e176ec18d2a91dbea1d0d1bd94c38dc47cd77c Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Fri, 15 May 2015 04:02:54 +0200
Subject: Separate block sampling functions

Refactoring ahead of tablesample patch

Requested and reviewed by Michael Paquier

Petr Jelinek
---
 src/include/utils/sampling.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 src/include/utils/sampling.h

(limited to 'src/include/utils/sampling.h')

diff --git a/src/include/utils/sampling.h b/src/include/utils/sampling.h
new file mode 100644
index 00000000000..e3e7f9cf6ae
--- /dev/null
+++ b/src/include/utils/sampling.h
@@ -0,0 +1,44 @@
+/*-------------------------------------------------------------------------
+ *
+ * sampling.h
+ *	  definitions for sampling functions
+ *
+ * Portions Copyright (c) 1996-2014, 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/bufmgr.h"
+
+extern double sampler_random_fract(void);
+
+/* 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 */
+} 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);
+
+/* Reservoid sampling methods */
+typedef double 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);
+
+#endif /* SAMPLING_H */
-- 
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