src/include/access/tsmapi.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * tsmapi.h
   4  *        API for tablesample methods
   5  *
   6  * Copyright (c) 2015-2021, PostgreSQL Global Development Group
   7  *
   8  * src/include/access/tsmapi.h
   9  *
  10  *-------------------------------------------------------------------------
  11  */
  12 #ifndef TSMAPI_H
  13 #define TSMAPI_H
  14
  15 #include "nodes/execnodes.h"
  16 #include "nodes/pathnodes.h"
  17
  18
  19 /*
  20  * Callback function signatures --- see tablesample-method.sgml for more info.
  21  */
  22
  23 typedef void (*SampleScanGetSampleSize_function) (PlannerInfo *root,
  24                                                                                                   RelOptInfo *baserel,
  25                                                                                                   List *paramexprs,
  26                                                                                                   BlockNumber *pages,
  27                                                                                                   double *tuples);
  28
  29 typedef void (*InitSampleScan_function) (SampleScanState *node,
  30                                                                                  int eflags);
  31
  32 typedef void (*BeginSampleScan_function) (SampleScanState *node,
  33                                                                                   Datum *params,
  34                                                                                   int nparams,
  35                                                                                   uint32 seed);
  36
  37 typedef BlockNumber (*NextSampleBlock_function) (SampleScanState *node,
  38                                                                                                  BlockNumber nblocks);
  39
  40 typedef OffsetNumber (*NextSampleTuple_function) (SampleScanState *node,
  41                                                                                                   BlockNumber blockno,
  42                                                                                                   OffsetNumber maxoffset);
  43
  44 typedef void (*EndSampleScan_function) (SampleScanState *node);
  45
  46 /*
  47  * TsmRoutine is the struct returned by a tablesample method's handler
  48  * function.  It provides pointers to the callback functions needed by the
  49  * planner and executor, as well as additional information about the method.
  50  *
  51  * More function pointers are likely to be added in the future.
  52  * Therefore it's recommended that the handler initialize the struct with
  53  * makeNode(TsmRoutine) so that all fields are set to NULL.  This will
  54  * ensure that no fields are accidentally left undefined.
  55  */
  56 typedef struct TsmRoutine
  57 {
  58         NodeTag         type;
  59
  60         /* List of datatype OIDs for the arguments of the TABLESAMPLE clause */
  61         List       *parameterTypes;
  62
  63         /* Can method produce repeatable samples across, or even within, queries? */
  64         bool            repeatable_across_queries;
  65         bool            repeatable_across_scans;
  66
  67         /* Functions for planning a SampleScan on a physical table */
  68         SampleScanGetSampleSize_function SampleScanGetSampleSize;
  69
  70         /* Functions for executing a SampleScan on a physical table */
  71         InitSampleScan_function InitSampleScan; /* can be NULL */
  72         BeginSampleScan_function BeginSampleScan;
  73         NextSampleBlock_function NextSampleBlock;       /* can be NULL */
  74         NextSampleTuple_function NextSampleTuple;
  75         EndSampleScan_function EndSampleScan;   /* can be NULL */
  76 } TsmRoutine;
  77
  78
  79 /* Functions in access/tablesample/tablesample.c */
  80 extern TsmRoutine *GetTsmRoutine(Oid tsmhandler);
  81
  82 #endif                                                  /* TSMAPI_H */