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db_include/access/tsmapi.h

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+/*-------------------------------------------------------------------------
+ *
+ * tsmapi.h
+ *	  API for tablesample methods
+ *
+ * Copyright (c) 2015-2021, PostgreSQL Global Development Group
+ *
+ * src/include/access/tsmapi.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef TSMAPI_H
+#define TSMAPI_H
+
+#include "nodes/execnodes.h"
+#include "nodes/pathnodes.h"
+
+
+/*
+ * Callback function signatures --- see tablesample-method.sgml for more info.
+ */
+
+typedef void (*SampleScanGetSampleSize_function) (PlannerInfo *root,
+												  RelOptInfo *baserel,
+												  List *paramexprs,
+												  BlockNumber *pages,
+												  double *tuples);
+
+typedef void (*InitSampleScan_function) (SampleScanState *node,
+										 int eflags);
+
+typedef void (*BeginSampleScan_function) (SampleScanState *node,
+										  Datum *params,
+										  int nparams,
+										  uint32 seed);
+
+typedef BlockNumber (*NextSampleBlock_function) (SampleScanState *node,
+												 BlockNumber nblocks);
+
+typedef OffsetNumber (*NextSampleTuple_function) (SampleScanState *node,
+												  BlockNumber blockno,
+												  OffsetNumber maxoffset);
+
+typedef void (*EndSampleScan_function) (SampleScanState *node);
+
+/*
+ * TsmRoutine is the struct returned by a tablesample method's handler
+ * function.  It provides pointers to the callback functions needed by the
+ * planner and executor, as well as additional information about the method.
+ *
+ * More function pointers are likely to be added in the future.
+ * Therefore it's recommended that the handler initialize the struct with
+ * makeNode(TsmRoutine) so that all fields are set to NULL.  This will
+ * ensure that no fields are accidentally left undefined.
+ */
+typedef struct TsmRoutine
+{
+	NodeTag		type;
+
+	/* List of datatype OIDs for the arguments of the TABLESAMPLE clause */
+	List	   *parameterTypes;
+
+	/* Can method produce repeatable samples across, or even within, queries? */
+	bool		repeatable_across_queries;
+	bool		repeatable_across_scans;
+
+	/* Functions for planning a SampleScan on a physical table */
+	SampleScanGetSampleSize_function SampleScanGetSampleSize;
+
+	/* Functions for executing a SampleScan on a physical table */
+	InitSampleScan_function InitSampleScan; /* can be NULL */
+	BeginSampleScan_function BeginSampleScan;
+	NextSampleBlock_function NextSampleBlock;	/* can be NULL */
+	NextSampleTuple_function NextSampleTuple;
+	EndSampleScan_function EndSampleScan;	/* can be NULL */
+} TsmRoutine;
+
+
+/* Functions in access/tablesample/tablesample.c */
+extern TsmRoutine *GetTsmRoutine(Oid tsmhandler);
+
+#endif							/* TSMAPI_H */