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TABLESAMPLE, SQL Standard and extensible

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Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.

Petr Jelinek

Reviewed by Michael Paquier and Simon Riggs
This commit is contained in:
Simon Riggs
2015-05-15 14:37:10 -04:00
parent 11a83bbedd
commit f6d208d6e5
66 changed files with 2756 additions and 40 deletions
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4
src/include/access/heapam.h
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@@ -114,8 +114,12 @@ extern HeapScanDesc heap_beginscan_strat(Relation relation, Snapshot snapshot,
bool allow_strat, bool allow_sync);
extern HeapScanDesc heap_beginscan_bm(Relation relation, Snapshot snapshot,
int nkeys, ScanKey key);
extern HeapScanDesc heap_beginscan_sampling(Relation relation,
Snapshot snapshot, int nkeys, ScanKey key,
bool allow_strat, bool allow_pagemode);
extern void heap_setscanlimits(HeapScanDesc scan, BlockNumber startBlk,
BlockNumber endBlk);
extern void heapgetpage(HeapScanDesc scan, BlockNumber page);
extern void heap_rescan(HeapScanDesc scan, ScanKey key);
extern void heap_endscan(HeapScanDesc scan);
extern HeapTuple heap_getnext(HeapScanDesc scan, ScanDirection direction);

1
src/include/access/relscan.h
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@@ -29,6 +29,7 @@ typedef struct HeapScanDescData
int rs_nkeys; /* number of scan keys */
ScanKey rs_key; /* array of scan key descriptors */
bool rs_bitmapscan; /* true if this is really a bitmap scan */
bool rs_samplescan; /* true if this is really a sample scan */
bool rs_pageatatime; /* verify visibility page-at-a-time? */
bool rs_allow_strat; /* allow or disallow use of access strategy */
bool rs_allow_sync; /* allow or disallow use of syncscan */

60
src/include/access/tablesample.h Normal file
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@@ -0,0 +1,60 @@
/*-------------------------------------------------------------------------
*
* tablesample.h
* Public header file for TABLESAMPLE clause interface
*
*
* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/tablesample.h
*
*-------------------------------------------------------------------------
*/
#ifndef TABLESAMPLE_H
#define TABLESAMPLE_H
#include "access/relscan.h"
#include "executor/executor.h"
typedef struct TableSampleDesc {
HeapScanDesc heapScan;
TupleDesc tupDesc; /* Mostly useful for tsmexaminetuple */
void *tsmdata; /* private method data */
/* These point to he function of the TABLESAMPLE Method. */
FmgrInfo tsminit;
FmgrInfo tsmnextblock;
FmgrInfo tsmnexttuple;
FmgrInfo tsmexaminetuple;
FmgrInfo tsmreset;
FmgrInfo tsmend;
} TableSampleDesc;
extern TableSampleDesc *tablesample_init(SampleScanState *scanstate,
TableSampleClause *tablesample);
extern HeapTuple tablesample_getnext(TableSampleDesc *desc);
extern void tablesample_reset(TableSampleDesc *desc);
extern void tablesample_end(TableSampleDesc *desc);
extern HeapTuple tablesample_source_getnext(TableSampleDesc *desc);
extern HeapTuple tablesample_source_gettup(TableSampleDesc *desc, ItemPointer tid,
bool *visible);
extern Datum tsm_system_init(PG_FUNCTION_ARGS);
extern Datum tsm_system_nextblock(PG_FUNCTION_ARGS);
extern Datum tsm_system_nexttuple(PG_FUNCTION_ARGS);
extern Datum tsm_system_end(PG_FUNCTION_ARGS);
extern Datum tsm_system_reset(PG_FUNCTION_ARGS);
extern Datum tsm_system_cost(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_init(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_nextblock(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_nexttuple(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_end(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_reset(PG_FUNCTION_ARGS);
extern Datum tsm_bernoulli_cost(PG_FUNCTION_ARGS);
#endif