tableam: Add and use scan APIs.

Too allow table accesses to be not directly dependent on heap, several
new abstractions are needed. Specifically:

1) Heap scans need to be generalized into table scans. Do this by
   introducing TableScanDesc, which will be the "base class" for
   individual AMs. This contains the AM independent fields from
   HeapScanDesc.

   The previous heap_{beginscan,rescan,endscan} et al. have been
   replaced with a table_ version.

   There's no direct replacement for heap_getnext(), as that returned
   a HeapTuple, which is undesirable for a other AMs. Instead there's
   table_scan_getnextslot().  But note that heap_getnext() lives on,
   it's still used widely to access catalog tables.

   This is achieved by new scan_begin, scan_end, scan_rescan,
   scan_getnextslot callbacks.

2) The portion of parallel scans that's shared between backends need
   to be able to do so without the user doing per-AM work. To achieve
   that new parallelscan_{estimate, initialize, reinitialize}
   callbacks are introduced, which operate on a new
   ParallelTableScanDesc, which again can be subclassed by AMs.

   As it is likely that several AMs are going to be block oriented,
   block oriented callbacks that can be shared between such AMs are
   provided and used by heap. table_block_parallelscan_{estimate,
   intiialize, reinitialize} as callbacks, and
   table_block_parallelscan_{nextpage, init} for use in AMs. These
   operate on a ParallelBlockTableScanDesc.

3) Index scans need to be able to access tables to return a tuple, and
   there needs to be state across individual accesses to the heap to
   store state like buffers. That's now handled by introducing a
   sort-of-scan IndexFetchTable, which again is intended to be
   subclassed by individual AMs (for heap IndexFetchHeap).

   The relevant callbacks for an AM are index_fetch_{end, begin,
   reset} to create the necessary state, and index_fetch_tuple to
   retrieve an indexed tuple.  Note that index_fetch_tuple
   implementations need to be smarter than just blindly fetching the
   tuples for AMs that have optimizations similar to heap's HOT - the
   currently alive tuple in the update chain needs to be fetched if
   appropriate.

   Similar to table_scan_getnextslot(), it's undesirable to continue
   to return HeapTuples. Thus index_fetch_heap (might want to rename
   that later) now accepts a slot as an argument. Core code doesn't
   have a lot of call sites performing index scans without going
   through the systable_* API (in contrast to loads of heap_getnext
   calls and working directly with HeapTuples).

   Index scans now store the result of a search in
   IndexScanDesc->xs_heaptid, rather than xs_ctup->t_self. As the
   target is not generally a HeapTuple anymore that seems cleaner.

To be able to sensible adapt code to use the above, two further
callbacks have been introduced:

a) slot_callbacks returns a TupleTableSlotOps* suitable for creating
   slots capable of holding a tuple of the AMs
   type. table_slot_callbacks() and table_slot_create() are based
   upon that, but have additional logic to deal with views, foreign
   tables, etc.

   While this change could have been done separately, nearly all the
   call sites that needed to be adapted for the rest of this commit
   also would have been needed to be adapted for
   table_slot_callbacks(), making separation not worthwhile.

b) tuple_satisfies_snapshot checks whether the tuple in a slot is
   currently visible according to a snapshot. That's required as a few
   places now don't have a buffer + HeapTuple around, but a
   slot (which in heap's case internally has that information).

Additionally a few infrastructure changes were needed:

I) SysScanDesc, as used by systable_{beginscan, getnext} et al. now
   internally uses a slot to keep track of tuples. While
   systable_getnext() still returns HeapTuples, and will so for the
   foreseeable future, the index API (see 1) above) now only deals with
   slots.

The remainder, and largest part, of this commit is then adjusting all
scans in postgres to use the new APIs.

Author: Andres Freund, Haribabu Kommi, Alvaro Herrera
Discussion:
    https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
    https://postgr.es/m/20160812231527.GA690404@alvherre.pgsql

1 files changed, 38 insertions, 36 deletions

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 5e74585d5e4..3a82857770c 100644
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -39,6 +39,7 @@
 
 #include "access/heapam.h"
 #include "access/relscan.h"
+#include "access/tableam.h"
 #include "access/transam.h"
 #include "access/visibilitymap.h"
 #include "executor/execdebug.h"
@@ -61,7 +62,7 @@ static inline void BitmapAdjustPrefetchIterator(BitmapHeapScanState *node,
 							 TBMIterateResult *tbmres);
 static inline void BitmapAdjustPrefetchTarget(BitmapHeapScanState *node);
 static inline void BitmapPrefetch(BitmapHeapScanState *node,
-			   HeapScanDesc scan);
+			   TableScanDesc scan);
 static bool BitmapShouldInitializeSharedState(
 								  ParallelBitmapHeapState *pstate);
 
@@ -76,7 +77,8 @@ static TupleTableSlot *
 BitmapHeapNext(BitmapHeapScanState *node)
 {
 	ExprContext *econtext;
-	HeapScanDesc scan;
+	TableScanDesc scan;
+	HeapScanDesc hscan;
 	TIDBitmap  *tbm;
 	TBMIterator *tbmiterator = NULL;
 	TBMSharedIterator *shared_tbmiterator = NULL;
@@ -92,6 +94,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 	econtext = node->ss.ps.ps_ExprContext;
 	slot = node->ss.ss_ScanTupleSlot;
 	scan = node->ss.ss_currentScanDesc;
+	hscan = (HeapScanDesc) scan;
 	tbm = node->tbm;
 	if (pstate == NULL)
 		tbmiterator = node->tbmiterator;
@@ -219,7 +222,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			 * least AccessShareLock on the table before performing any of the
 			 * indexscans, but let's be safe.)
 			 */
-			if (tbmres->blockno >= scan->rs_nblocks)
+			if (tbmres->blockno >= hscan->rs_nblocks)
 			{
 				node->tbmres = tbmres = NULL;
 				continue;
@@ -242,14 +245,14 @@ BitmapHeapNext(BitmapHeapScanState *node)
 				 * The number of tuples on this page is put into
 				 * scan->rs_ntuples; note we don't fill scan->rs_vistuples.
 				 */
-				scan->rs_ntuples = tbmres->ntuples;
+				hscan->rs_ntuples = tbmres->ntuples;
 			}
 			else
 			{
 				/*
 				 * Fetch the current heap page and identify candidate tuples.
 				 */
-				bitgetpage(scan, tbmres);
+				bitgetpage(hscan, tbmres);
 			}
 
 			if (tbmres->ntuples >= 0)
@@ -260,7 +263,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			/*
 			 * Set rs_cindex to first slot to examine
 			 */
-			scan->rs_cindex = 0;
+			hscan->rs_cindex = 0;
 
 			/* Adjust the prefetch target */
 			BitmapAdjustPrefetchTarget(node);
@@ -270,7 +273,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			/*
 			 * Continuing in previously obtained page; advance rs_cindex
 			 */
-			scan->rs_cindex++;
+			hscan->rs_cindex++;
 
 #ifdef USE_PREFETCH
 
@@ -297,7 +300,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
 		/*
 		 * Out of range?  If so, nothing more to look at on this page
 		 */
-		if (scan->rs_cindex < 0 || scan->rs_cindex >= scan->rs_ntuples)
+		if (hscan->rs_cindex < 0 || hscan->rs_cindex >= hscan->rs_ntuples)
 		{
 			node->tbmres = tbmres = NULL;
 			continue;
@@ -324,15 +327,15 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			/*
 			 * Okay to fetch the tuple.
 			 */
-			targoffset = scan->rs_vistuples[scan->rs_cindex];
-			dp = (Page) BufferGetPage(scan->rs_cbuf);
+			targoffset = hscan->rs_vistuples[hscan->rs_cindex];
+			dp = (Page) BufferGetPage(hscan->rs_cbuf);
 			lp = PageGetItemId(dp, targoffset);
 			Assert(ItemIdIsNormal(lp));
 
-			scan->rs_ctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
-			scan->rs_ctup.t_len = ItemIdGetLength(lp);
-			scan->rs_ctup.t_tableOid = scan->rs_rd->rd_id;
-			ItemPointerSet(&scan->rs_ctup.t_self, tbmres->blockno, targoffset);
+			hscan->rs_ctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
+			hscan->rs_ctup.t_len = ItemIdGetLength(lp);
+			hscan->rs_ctup.t_tableOid = scan->rs_rd->rd_id;
+			ItemPointerSet(&hscan->rs_ctup.t_self, tbmres->blockno, targoffset);
 
 			pgstat_count_heap_fetch(scan->rs_rd);
 
@@ -340,9 +343,9 @@ BitmapHeapNext(BitmapHeapScanState *node)
 			 * Set up the result slot to point to this tuple.  Note that the
 			 * slot acquires a pin on the buffer.
 			 */
-			ExecStoreBufferHeapTuple(&scan->rs_ctup,
+			ExecStoreBufferHeapTuple(&hscan->rs_ctup,
 									 slot,
-									 scan->rs_cbuf);
+									 hscan->rs_cbuf);
 
 			/*
 			 * If we are using lossy info, we have to recheck the qual
@@ -392,17 +395,17 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
 	Assert(page < scan->rs_nblocks);
 
 	scan->rs_cbuf = ReleaseAndReadBuffer(scan->rs_cbuf,
-										 scan->rs_rd,
+										 scan->rs_base.rs_rd,
 										 page);
 	buffer = scan->rs_cbuf;
-	snapshot = scan->rs_snapshot;
+	snapshot = scan->rs_base.rs_snapshot;
 
 	ntup = 0;
 
 	/*
 	 * Prune and repair fragmentation for the whole page, if possible.
 	 */
-	heap_page_prune_opt(scan->rs_rd, buffer);
+	heap_page_prune_opt(scan->rs_base.rs_rd, buffer);
 
 	/*
 	 * We must hold share lock on the buffer content while examining tuple
@@ -430,8 +433,8 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
 			HeapTupleData heapTuple;
 
 			ItemPointerSet(&tid, page, offnum);
-			if (heap_hot_search_buffer(&tid, scan->rs_rd, buffer, snapshot,
-									   &heapTuple, NULL, true))
+			if (heap_hot_search_buffer(&tid, scan->rs_base.rs_rd, buffer,
+									   snapshot, &heapTuple, NULL, true))
 				scan->rs_vistuples[ntup++] = ItemPointerGetOffsetNumber(&tid);
 		}
 	}
@@ -456,16 +459,16 @@ bitgetpage(HeapScanDesc scan, TBMIterateResult *tbmres)
 				continue;
 			loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
 			loctup.t_len = ItemIdGetLength(lp);
-			loctup.t_tableOid = scan->rs_rd->rd_id;
+			loctup.t_tableOid = scan->rs_base.rs_rd->rd_id;
 			ItemPointerSet(&loctup.t_self, page, offnum);
 			valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
 			if (valid)
 			{
 				scan->rs_vistuples[ntup++] = offnum;
-				PredicateLockTuple(scan->rs_rd, &loctup, snapshot);
+				PredicateLockTuple(scan->rs_base.rs_rd, &loctup, snapshot);
 			}
-			CheckForSerializableConflictOut(valid, scan->rs_rd, &loctup,
-											buffer, snapshot);
+			CheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
+											&loctup, buffer, snapshot);
 		}
 	}
 
@@ -598,7 +601,7 @@ BitmapAdjustPrefetchTarget(BitmapHeapScanState *node)
  * BitmapPrefetch - Prefetch, if prefetch_pages are behind prefetch_target
  */
 static inline void
-BitmapPrefetch(BitmapHeapScanState *node, HeapScanDesc scan)
+BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan)
 {
 #ifdef USE_PREFETCH
 	ParallelBitmapHeapState *pstate = node->pstate;
@@ -741,7 +744,7 @@ ExecReScanBitmapHeapScan(BitmapHeapScanState *node)
 	PlanState  *outerPlan = outerPlanState(node);
 
 	/* rescan to release any page pin */
-	heap_rescan(node->ss.ss_currentScanDesc, NULL);
+	table_rescan(node->ss.ss_currentScanDesc, NULL);
 
 	/* release bitmaps and buffers if any */
 	if (node->tbmiterator)
@@ -785,7 +788,7 @@ ExecReScanBitmapHeapScan(BitmapHeapScanState *node)
 void
 ExecEndBitmapHeapScan(BitmapHeapScanState *node)
 {
-	HeapScanDesc scanDesc;
+	TableScanDesc scanDesc;
 
 	/*
 	 * extract information from the node
@@ -830,7 +833,7 @@ ExecEndBitmapHeapScan(BitmapHeapScanState *node)
 	/*
 	 * close heap scan
 	 */
-	heap_endscan(scanDesc);
+	table_endscan(scanDesc);
 }
 
 /* ----------------------------------------------------------------
@@ -914,8 +917,7 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
 	 */
 	ExecInitScanTupleSlot(estate, &scanstate->ss,
 						  RelationGetDescr(currentRelation),
-						  &TTSOpsBufferHeapTuple);
-
+						  table_slot_callbacks(currentRelation));
 
 	/*
 	 * Initialize result type and projection.
@@ -953,10 +955,10 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
 	 * Even though we aren't going to do a conventional seqscan, it is useful
 	 * to create a HeapScanDesc --- most of the fields in it are usable.
 	 */
-	scanstate->ss.ss_currentScanDesc = heap_beginscan_bm(currentRelation,
-														 estate->es_snapshot,
-														 0,
-														 NULL);
+	scanstate->ss.ss_currentScanDesc = table_beginscan_bm(currentRelation,
+														  estate->es_snapshot,
+														  0,
+														  NULL);
 
 	/*
 	 * all done.
@@ -1104,5 +1106,5 @@ ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
 	node->pstate = pstate;
 
 	snapshot = RestoreSnapshot(pstate->phs_snapshot_data);
-	heap_update_snapshot(node->ss.ss_currentScanDesc, snapshot);
+	table_scan_update_snapshot(node->ss.ss_currentScanDesc, snapshot);
 }