Redesign tablesample method API, and do extensive code review.

The original implementation of TABLESAMPLE modeled the tablesample method
API on index access methods, which wasn't a good choice because, without
specialized DDL commands, there's no way to build an extension that can
implement a TSM.  (Raw inserts into system catalogs are not an acceptable
thing to do, because we can't undo them during DROP EXTENSION, nor will
pg_upgrade behave sanely.)  Instead adopt an API more like procedural
language handlers or foreign data wrappers, wherein the only SQL-level
support object needed is a single handler function identified by having
a special return type.  This lets us get rid of the supporting catalog
altogether, so that no custom DDL support is needed for the feature.

Adjust the API so that it can support non-constant tablesample arguments
(the original coding assumed we could evaluate the argument expressions at
ExecInitSampleScan time, which is undesirable even if it weren't outright
unsafe), and discourage sampling methods from looking at invisible tuples.
Make sure that the BERNOULLI and SYSTEM methods are genuinely repeatable
within and across queries, as required by the SQL standard, and deal more
honestly with methods that can't support that requirement.

Make a full code-review pass over the tablesample additions, and fix
assorted bugs, omissions, infelicities, and cosmetic issues (such as
failure to put the added code stanzas in a consistent ordering).
Improve EXPLAIN's output of tablesample plans, too.

Back-patch to 9.5 so that we don't have to support the original API
in production.

1 files changed, 0 insertions, 61 deletions

diff --git a/src/include/access/tablesample.h b/src/include/access/tablesample.h
deleted file mode 100644
index a02e93d3222..00000000000
--- a/src/include/access/tablesample.h
+++ /dev/null
@@ -1,61 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * 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