From 9846d4e9d845d25c9b57a054b42803019e41c0e5 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Mon, 26 Aug 2024 04:45:47 +0000
Subject: [PATCH v23 1/5] Introduce new Table AM for multi inserts

Until now, it's the COPY ... FROM command using multi inserts
(i.e. buffer some tuples and inserts them to table at once).
Various other commands can benefit from this multi insert
logic [Reusable].

Also, there's a need to have these multi insert AMs
(Access Methods) as scan-like API [Usability].

Also, there's a need allow various table AMs define their own
buffering and flushing strategy [Flexibility].

This commit introduces, new table AMs for multi inserts to help
achieve all of the above.

Upcoming commits will have these new table AMs being used for
various other commands.

Author: Bharath Rupireddy
Reviewed-by: Jeff Davis
Discussion: https://www.postgresql.org/message-id/20200924024128.kyk3r5g7dnu3fxxx@alap3.anarazel.de
Discussion: https://www.postgresql.org/message-id/CALj2ACVi9eTRYR%3Dgdca5wxtj3Kk_9q9qVccxsS1hngTGOCjPwQ%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/8633171cb034aafc260fdf37df04b6c779aa1e2f.camel%40j-davis.com
---
 src/backend/access/heap/heapam.c         | 197 ++++++++++++++++++++++-
 src/backend/access/heap/heapam_handler.c |   6 +
 src/backend/access/table/tableamapi.c    |   5 +
 src/include/access/heapam.h              |  38 +++++
 src/include/access/tableam.h             |  80 +++++++++
 src/tools/pgindent/typedefs.list         |   3 +
 6 files changed, 328 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 91b20147a0..86d60e476b 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -65,6 +65,7 @@
 #include "utils/datum.h"
 #include "utils/injection_point.h"
 #include "utils/inval.h"
+#include "utils/memutils.h"
 #include "utils/relcache.h"
 #include "utils/snapmgr.h"
 #include "utils/spccache.h"
@@ -113,7 +114,7 @@ static int	bottomup_sort_and_shrink(TM_IndexDeleteOp *delstate);
 static XLogRecPtr log_heap_new_cid(Relation relation, HeapTuple tup);
 static HeapTuple ExtractReplicaIdentity(Relation relation, HeapTuple tp, bool key_required,
 										bool *copy);
-
+static void heap_modify_insert_end_callback(TableModifyState *state);
 
 /*
  * Each tuple lock mode has a corresponding heavyweight lock, and one or two
@@ -2612,6 +2613,200 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
 	pgstat_count_heap_insert(relation, ntuples);
 }
 
+/*
+ * Initialize heap modify state.
+ */
+TableModifyState *
+heap_modify_begin(Relation rel, int modify_flags,
+				  CommandId cid, int options,
+				  TableModifyBufferFlushCallback modify_buffer_flush_callback,
+				  void *modify_buffer_flush_context)
+{
+	TableModifyState *state;
+	MemoryContext context;
+	MemoryContext oldcontext;
+
+	context = AllocSetContextCreate(TopTransactionContext,
+									"heap_modify memory context",
+									ALLOCSET_DEFAULT_SIZES);
+
+	oldcontext = MemoryContextSwitchTo(context);
+	state = palloc0(sizeof(TableModifyState));
+	state->rel = rel;
+	state->modify_flags = modify_flags;
+	state->mem_cxt = context;
+	state->cid = cid;
+	state->options = options;
+	state->modify_buffer_flush_callback = modify_buffer_flush_callback;
+	state->modify_buffer_flush_context = modify_buffer_flush_context;
+	state->modify_end_callback = NULL;	/* To be installed lazily */
+	MemoryContextSwitchTo(oldcontext);
+
+	return state;
+}
+
+/*
+ * Store passed-in tuple into in-memory buffered slots. When full, insert
+ * multiple tuples from the buffers into heap.
+ */
+void
+heap_modify_buffer_insert(TableModifyState *state,
+						  TupleTableSlot *slot)
+{
+	TupleTableSlot *dstslot;
+	HeapInsertState *istate;
+	HeapMultiInsertState *mistate;
+	MemoryContext oldcontext;
+
+	oldcontext = MemoryContextSwitchTo(state->mem_cxt);
+
+	/* First time through, initialize heap insert state */
+	if (state->data == NULL)
+	{
+		istate = (HeapInsertState *) palloc0(sizeof(HeapInsertState));
+		istate->bistate = NULL;
+		istate->mistate = NULL;
+		state->data = istate;
+		mistate = (HeapMultiInsertState *) palloc0(sizeof(HeapMultiInsertState));
+		mistate->slots = (TupleTableSlot **) palloc0(sizeof(TupleTableSlot *) * HEAP_MAX_BUFFERED_SLOTS);
+		istate->mistate = mistate;
+		mistate->mem_cxt = AllocSetContextCreate(CurrentMemoryContext,
+												 "heap_multi_insert memory context",
+												 ALLOCSET_DEFAULT_SIZES);
+
+		if ((state->modify_flags & TM_FLAG_BAS_BULKWRITE) != 0)
+			istate->bistate = GetBulkInsertState();
+
+		state->modify_end_callback = heap_modify_insert_end_callback;
+	}
+
+	istate = (HeapInsertState *) state->data;
+	Assert(istate->mistate != NULL);
+	mistate = istate->mistate;
+
+	dstslot = mistate->slots[mistate->cur_slots];
+	if (dstslot == NULL)
+	{
+		/*
+		 * We use virtual tuple slots buffered slots for leveraging the
+		 * optimization it provides to minimize physical data copying. The
+		 * virtual slot gets materialized when we copy (via below
+		 * ExecCopySlot) the tuples from the source slot which can be of any
+		 * type. This way, it is ensured that the tuple storage doesn't depend
+		 * on external memory, because all the datums that aren't passed by
+		 * value are copied into the slot's memory context.
+		 */
+		dstslot = MakeTupleTableSlot(RelationGetDescr(state->rel),
+									 &TTSOpsVirtual);
+		mistate->slots[mistate->cur_slots] = dstslot;
+	}
+
+	Assert(TTS_IS_VIRTUAL(dstslot));
+
+	/*
+	 * Note that the copy clears the previous destination slot contents, so
+	 * there's no need of explicit ExecClearTuple here.
+	 */
+	ExecCopySlot(dstslot, slot);
+
+	mistate->cur_slots++;
+
+	if (mistate->cur_slots >= HEAP_MAX_BUFFERED_SLOTS)
+		heap_modify_buffer_flush(state);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+/*
+ * Insert multiple tuples from in-memory buffered slots into heap.
+ */
+void
+heap_modify_buffer_flush(TableModifyState *state)
+{
+	HeapInsertState *istate;
+	HeapMultiInsertState *mistate;
+	MemoryContext oldcontext;
+
+	/* Quick exit if we haven't inserted anything yet */
+	if (state->data == NULL)
+		return;
+
+	istate = (HeapInsertState *) state->data;
+	Assert(istate->mistate != NULL);
+	mistate = istate->mistate;
+
+	/* Quick exit if we have flushed already */
+	if (mistate->cur_slots == 0)
+		return;
+
+	/*
+	 * heap_multi_insert may leak memory, so switch to short-lived memory
+	 * context before calling it.
+	 */
+	oldcontext = MemoryContextSwitchTo(mistate->mem_cxt);
+
+	heap_multi_insert(state->rel, mistate->slots, mistate->cur_slots,
+					  state->cid, state->options, istate->bistate);
+
+	MemoryContextSwitchTo(oldcontext);
+	MemoryContextReset(mistate->mem_cxt);
+
+	if (state->modify_buffer_flush_callback != NULL)
+	{
+		for (int i = 0; i < mistate->cur_slots; i++)
+			state->modify_buffer_flush_callback(state->modify_buffer_flush_context,
+												mistate->slots[i]);
+	}
+
+	mistate->cur_slots = 0;
+}
+
+/*
+ * Heap insert specific callback used for performing work at the end like
+ * flushing buffered tuples if any, cleaning up the insert state and buffered
+ * slots.
+ */
+static void
+heap_modify_insert_end_callback(TableModifyState *state)
+{
+	HeapInsertState *istate;
+
+	/* Quick exit if we haven't inserted anything yet */
+	if (state->data == NULL)
+		return;
+
+	istate = (HeapInsertState *) state->data;
+
+	if (istate->mistate != NULL)
+	{
+		HeapMultiInsertState *mistate = istate->mistate;
+
+		heap_modify_buffer_flush(state);
+
+		Assert(mistate->cur_slots == 0);
+
+		for (int i = 0; i < HEAP_MAX_BUFFERED_SLOTS && mistate->slots[i] != NULL; i++)
+			ExecDropSingleTupleTableSlot(mistate->slots[i]);
+
+		MemoryContextDelete(mistate->mem_cxt);
+	}
+
+	if (istate->bistate != NULL)
+		FreeBulkInsertState(istate->bistate);
+}
+
+/*
+ * Clean heap modify state.
+ */
+void
+heap_modify_end(TableModifyState *state)
+{
+	if (state->modify_end_callback != NULL)
+		state->modify_end_callback(state);
+
+	MemoryContextDelete(state->mem_cxt);
+}
+
 /*
  *	simple_heap_insert - insert a tuple
  *
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index 1c6da286d4..3cacfdf871 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2611,6 +2611,12 @@ static const TableAmRoutine heapam_methods = {
 	.tuple_insert_speculative = heapam_tuple_insert_speculative,
 	.tuple_complete_speculative = heapam_tuple_complete_speculative,
 	.multi_insert = heap_multi_insert,
+
+	.tuple_modify_begin = heap_modify_begin,
+	.tuple_modify_buffer_insert = heap_modify_buffer_insert,
+	.tuple_modify_buffer_flush = heap_modify_buffer_flush,
+	.tuple_modify_end = heap_modify_end,
+
 	.tuple_delete = heapam_tuple_delete,
 	.tuple_update = heapam_tuple_update,
 	.tuple_lock = heapam_tuple_lock,
diff --git a/src/backend/access/table/tableamapi.c b/src/backend/access/table/tableamapi.c
index e9b598256f..772f29b1b5 100644
--- a/src/backend/access/table/tableamapi.c
+++ b/src/backend/access/table/tableamapi.c
@@ -97,6 +97,11 @@ GetTableAmRoutine(Oid amhandler)
 	Assert(routine->scan_sample_next_block != NULL);
 	Assert(routine->scan_sample_next_tuple != NULL);
 
+	Assert(routine->tuple_modify_begin != NULL);
+	Assert(routine->tuple_modify_buffer_insert != NULL);
+	Assert(routine->tuple_modify_buffer_flush != NULL);
+	Assert(routine->tuple_modify_end != NULL);
+
 	return routine;
 }
 
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 9e9aec88a6..8c44a7808d 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -271,6 +271,32 @@ typedef enum
 	PRUNE_VACUUM_CLEANUP,		/* VACUUM 2nd heap pass */
 } PruneReason;
 
+/*
+ * Maximum number of slots that multi-insert buffers can hold.
+ *
+ * Caution: Don't make this too big, as we could end up with this many tuples
+ * stored in multi insert buffer.
+ */
+#define HEAP_MAX_BUFFERED_SLOTS		1000
+
+typedef struct HeapMultiInsertState
+{
+	/* Array of buffered slots */
+	TupleTableSlot **slots;
+
+	/* Number of buffered slots currently held */
+	int			cur_slots;
+
+	MemoryContext mem_cxt;
+} HeapMultiInsertState;
+
+typedef struct HeapInsertState
+{
+	struct BulkInsertStateData *bistate;
+	HeapMultiInsertState *mistate;
+} HeapInsertState;
+
+
 /* ----------------
  *		function prototypes for heap access method
  *
@@ -321,6 +347,18 @@ extern void heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 extern void heap_multi_insert(Relation relation, struct TupleTableSlot **slots,
 							  int ntuples, CommandId cid, int options,
 							  BulkInsertState bistate);
+
+extern TableModifyState *heap_modify_begin(Relation rel,
+										   int modify_flags,
+										   CommandId cid,
+										   int options,
+										   TableModifyBufferFlushCallback modify_buffer_flush_callback,
+										   void *modify_buffer_flush_context);
+extern void heap_modify_buffer_insert(TableModifyState *state,
+									  TupleTableSlot *slot);
+extern void heap_modify_buffer_flush(TableModifyState *state);
+extern void heap_modify_end(TableModifyState *state);
+
 extern TM_Result heap_delete(Relation relation, ItemPointer tid,
 							 CommandId cid, Snapshot crosscheck, bool wait,
 							 struct TM_FailureData *tmfd, bool changingPart);
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index da661289c1..083d9ac820 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -255,6 +255,39 @@ typedef struct TM_IndexDeleteOp
 	TM_IndexStatus *status;
 } TM_IndexDeleteOp;
 
+/* Table modify flags */
+
+/* Use BAS_BULKWRITE buffer access strategy */
+#define TM_FLAG_BAS_BULKWRITE	0x000001
+
+struct TableModifyState;
+
+/* Callback invoked for each tuple that gets flushed to disk from buffer */
+typedef void (*TableModifyBufferFlushCallback) (void *context,
+												TupleTableSlot *slot);
+
+/* Table AM specific callback that gets called in table_modify_end() */
+typedef void (*TableModifyEndCallback) (struct TableModifyState *state);
+
+/* Holds table modify state */
+typedef struct TableModifyState
+{
+	Relation	rel;
+	int			modify_flags;
+	MemoryContext mem_cxt;
+	CommandId	cid;
+	int			options;
+
+	/* Flush callback and its context */
+	TableModifyBufferFlushCallback modify_buffer_flush_callback;
+	void	   *modify_buffer_flush_context;
+
+	/* Table AM specific data */
+	void	   *data;
+
+	TableModifyEndCallback modify_end_callback;
+} TableModifyState;
+
 /* "options" flag bits for table_tuple_insert */
 /* TABLE_INSERT_SKIP_WAL was 0x0001; RelationNeedsWAL() now governs */
 #define TABLE_INSERT_SKIP_FSM		0x0002
@@ -578,6 +611,21 @@ typedef struct TableAmRoutine
 	void		(*finish_bulk_insert) (Relation rel, int options);
 
 
+	/* ------------------------------------------------------------------------
+	 * Table Modify related functions.
+	 * ------------------------------------------------------------------------
+	 */
+	TableModifyState *(*tuple_modify_begin) (Relation rel,
+											 int modify_flags,
+											 CommandId cid,
+											 int options,
+											 TableModifyBufferFlushCallback modify_buffer_flush_callback,
+											 void *modify_buffer_flush_context);
+	void		(*tuple_modify_buffer_insert) (TableModifyState *state,
+											   TupleTableSlot *slot);
+	void		(*tuple_modify_buffer_flush) (TableModifyState *state);
+	void		(*tuple_modify_end) (TableModifyState *state);
+
 	/* ------------------------------------------------------------------------
 	 * DDL related functionality.
 	 * ------------------------------------------------------------------------
@@ -1599,6 +1647,38 @@ table_finish_bulk_insert(Relation rel, int options)
 		rel->rd_tableam->finish_bulk_insert(rel, options);
 }
 
+/* ------------------------------------------------------------------------
+ * Table Modify related functions.
+ * ------------------------------------------------------------------------
+ */
+static inline TableModifyState *
+table_modify_begin(Relation rel, int modify_flags, CommandId cid, int options,
+				   TableModifyBufferFlushCallback modify_buffer_flush_callback,
+				   void *modify_buffer_flush_context)
+{
+	return rel->rd_tableam->tuple_modify_begin(rel, modify_flags,
+											   cid, options,
+											   modify_buffer_flush_callback,
+											   modify_buffer_flush_context);
+}
+
+static inline void
+table_modify_buffer_insert(TableModifyState *state, TupleTableSlot *slot)
+{
+	state->rel->rd_tableam->tuple_modify_buffer_insert(state, slot);
+}
+
+static inline void
+table_modify_buffer_flush(TableModifyState *state)
+{
+	state->rel->rd_tableam->tuple_modify_buffer_flush(state);
+}
+
+static inline void
+table_modify_end(TableModifyState *state)
+{
+	state->rel->rd_tableam->tuple_modify_end(state);
+}
 
 /* ------------------------------------------------------------------------
  * DDL related functionality.
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 9e951a9e6f..538132e6f4 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1145,6 +1145,8 @@ HeadlineJsonState
 HeadlineParsedText
 HeadlineWordEntry
 HeapCheckContext
+HeapInsertState
+HeapMultiInsertState
 HeapPageFreeze
 HeapScanDesc
 HeapTuple
@@ -2869,6 +2871,7 @@ TableFuncScanState
 TableFuncType
 TableInfo
 TableLikeClause
+TableModifyState
 TableSampleClause
 TableScanDesc
 TableScanDescData
-- 
2.43.0

