/*-------------------------------------------------------------------------
 *
 * heapam_handler.c
 *	  heap table access method code
 *
 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/access/heap/heapam_handler.c
 *
 *
 * NOTES
 *	  This files wires up the lower level heapam.c et routines with the
 *	  tableam abstraction.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "utils/builtins.h"


static const TableAmRoutine heapam_methods;


/* ------------------------------------------------------------------------
 * Slot related callbacks for heap AM
 * ------------------------------------------------------------------------
 */

static const TupleTableSlotOps *
heapam_slot_callbacks(Relation relation)
{
	return &TTSOpsBufferHeapTuple;
}


/* ------------------------------------------------------------------------
 * Index Scan Callbacks for heap AM
 * ------------------------------------------------------------------------
 */

static IndexFetchTableData *
heapam_index_fetch_begin(Relation rel)
{
	IndexFetchHeapData *hscan = palloc0(sizeof(IndexFetchHeapData));

	hscan->xs_base.rel = rel;
	hscan->xs_cbuf = InvalidBuffer;

	return &hscan->xs_base;
}

static void
heapam_index_fetch_reset(IndexFetchTableData *scan)
{
	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;

	if (BufferIsValid(hscan->xs_cbuf))
	{
		ReleaseBuffer(hscan->xs_cbuf);
		hscan->xs_cbuf = InvalidBuffer;
	}
}

static void
heapam_index_fetch_end(IndexFetchTableData *scan)
{
	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;

	heapam_index_fetch_reset(scan);

	pfree(hscan);
}

static bool
heapam_index_fetch_tuple(struct IndexFetchTableData *scan,
						 ItemPointer tid,
						 Snapshot snapshot,
						 TupleTableSlot *slot,
						 bool *call_again, bool *all_dead)
{
	IndexFetchHeapData *hscan = (IndexFetchHeapData *) scan;
	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
	bool		got_heap_tuple;

	Assert(TTS_IS_BUFFERTUPLE(slot));

	/* We can skip the buffer-switching logic if we're in mid-HOT chain. */
	if (!*call_again)
	{
		/* Switch to correct buffer if we don't have it already */
		Buffer		prev_buf = hscan->xs_cbuf;

		hscan->xs_cbuf = ReleaseAndReadBuffer(hscan->xs_cbuf,
											  hscan->xs_base.rel,
											  ItemPointerGetBlockNumber(tid));

		/*
		 * Prune page, but only if we weren't already on this page
		 */
		if (prev_buf != hscan->xs_cbuf)
			heap_page_prune_opt(hscan->xs_base.rel, hscan->xs_cbuf);
	}

	/* Obtain share-lock on the buffer so we can examine visibility */
	LockBuffer(hscan->xs_cbuf, BUFFER_LOCK_SHARE);
	got_heap_tuple = heap_hot_search_buffer(tid,
											hscan->xs_base.rel,
											hscan->xs_cbuf,
											snapshot,
											&bslot->base.tupdata,
											all_dead,
											!*call_again);
	bslot->base.tupdata.t_self = *tid;
	LockBuffer(hscan->xs_cbuf, BUFFER_LOCK_UNLOCK);

	if (got_heap_tuple)
	{
		/*
		 * Only in a non-MVCC snapshot can more than one member of the HOT
		 * chain be visible.
		 */
		*call_again = !IsMVCCSnapshot(snapshot);

		slot->tts_tableOid = RelationGetRelid(scan->rel);
		ExecStoreBufferHeapTuple(&bslot->base.tupdata, slot, hscan->xs_cbuf);
	}
	else
	{
		/* We've reached the end of the HOT chain. */
		*call_again = false;
	}

	return got_heap_tuple;
}


/* ------------------------------------------------------------------------
 * Callbacks for non-modifying operations on individual tuples for heap AM
 * ------------------------------------------------------------------------
 */

static bool
heapam_fetch_row_version(Relation relation,
						 ItemPointer tid,
						 Snapshot snapshot,
						 TupleTableSlot *slot)
{
	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
	Buffer		buffer;

	Assert(TTS_IS_BUFFERTUPLE(slot));

	bslot->base.tupdata.t_self = *tid;
	if (heap_fetch(relation, snapshot, &bslot->base.tupdata, &buffer))
	{
		/* store in slot, transferring existing pin */
		ExecStorePinnedBufferHeapTuple(&bslot->base.tupdata, slot, buffer);
		slot->tts_tableOid = RelationGetRelid(relation);

		return true;
	}

	return false;
}

static bool
heapam_tuple_satisfies_snapshot(Relation rel, TupleTableSlot *slot,
								Snapshot snapshot)
{
	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
	bool		res;

	Assert(TTS_IS_BUFFERTUPLE(slot));
	Assert(BufferIsValid(bslot->buffer));

	/*
	 * We need buffer pin and lock to call HeapTupleSatisfiesVisibility.
	 * Caller should be holding pin, but not lock.
	 */
	LockBuffer(bslot->buffer, BUFFER_LOCK_SHARE);
	res = HeapTupleSatisfiesVisibility(bslot->base.tuple, snapshot,
									   bslot->buffer);
	LockBuffer(bslot->buffer, BUFFER_LOCK_UNLOCK);

	return res;
}


/* ----------------------------------------------------------------------------
 *  Functions for manipulations of physical tuples for heap AM.
 * ----------------------------------------------------------------------------
 */

static void
heapam_tuple_insert(Relation relation, TupleTableSlot *slot, CommandId cid,
					int options, BulkInsertState bistate)
{
	bool		shouldFree = true;
	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);

	/* Update the tuple with table oid */
	slot->tts_tableOid = RelationGetRelid(relation);
	tuple->t_tableOid = slot->tts_tableOid;

	/* Perform the insertion, and copy the resulting ItemPointer */
	heap_insert(relation, tuple, cid, options, bistate);
	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);

	if (shouldFree)
		pfree(tuple);
}

static void
heapam_tuple_insert_speculative(Relation relation, TupleTableSlot *slot, CommandId cid,
								int options, BulkInsertState bistate, uint32 specToken)
{
	bool		shouldFree = true;
	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);

	/* Update the tuple with table oid */
	slot->tts_tableOid = RelationGetRelid(relation);
	tuple->t_tableOid = slot->tts_tableOid;

	HeapTupleHeaderSetSpeculativeToken(tuple->t_data, specToken);
	options |= HEAP_INSERT_SPECULATIVE;

	/* Perform the insertion, and copy the resulting ItemPointer */
	heap_insert(relation, tuple, cid, options, bistate);
	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);

	if (shouldFree)
		pfree(tuple);
}

static void
heapam_tuple_complete_speculative(Relation relation, TupleTableSlot *slot, uint32 spekToken,
								  bool succeeded)
{
	bool		shouldFree = true;
	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);

	/* adjust the tuple's state accordingly */
	if (!succeeded)
		heap_finish_speculative(relation, &slot->tts_tid);
	else
		heap_abort_speculative(relation, &slot->tts_tid);

	if (shouldFree)
		pfree(tuple);
}

static TM_Result
heapam_tuple_delete(Relation relation, ItemPointer tid, CommandId cid,
					Snapshot snapshot, Snapshot crosscheck, bool wait,
					TM_FailureData *tmfd, bool changingPart)
{
	/*
	 * Currently Deleting of index tuples are handled at vacuum, in case if
	 * the storage itself is cleaning the dead tuples by itself, it is the
	 * time to call the index tuple deletion also.
	 */
	return heap_delete(relation, tid, cid, crosscheck, wait, tmfd, changingPart);
}


static TM_Result
heapam_tuple_update(Relation relation, ItemPointer otid, TupleTableSlot *slot,
					CommandId cid, Snapshot snapshot, Snapshot crosscheck,
					bool wait, TM_FailureData *tmfd,
					LockTupleMode *lockmode, bool *update_indexes)
{
	bool		shouldFree = true;
	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
	TM_Result	result;

	/* Update the tuple with table oid */
	slot->tts_tableOid = RelationGetRelid(relation);
	tuple->t_tableOid = slot->tts_tableOid;

	result = heap_update(relation, otid, tuple, cid, crosscheck, wait,
						 tmfd, lockmode);
	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);

	/*
	 * Decide whether new index entries are needed for the tuple
	 *
	 * Note: heap_update returns the tid (location) of the new tuple in the
	 * t_self field.
	 *
	 * If it's a HOT update, we mustn't insert new index entries.
	 */
	*update_indexes = result == TM_Ok && !HeapTupleIsHeapOnly(tuple);

	if (shouldFree)
		pfree(tuple);

	return result;
}

static TM_Result
heapam_tuple_lock(Relation relation, ItemPointer tid, Snapshot snapshot,
				  TupleTableSlot *slot, CommandId cid, LockTupleMode mode,
				  LockWaitPolicy wait_policy, uint8 flags,
				  TM_FailureData *tmfd)
{
	BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
	TM_Result	result;
	Buffer		buffer;
	HeapTuple	tuple = &bslot->base.tupdata;
	bool		follow_updates;

	follow_updates = (flags & TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS) != 0;
	tmfd->traversed = false;

	Assert(TTS_IS_BUFFERTUPLE(slot));

tuple_lock_retry:
	tuple->t_self = *tid;
	result = heap_lock_tuple(relation, tuple, cid, mode, wait_policy,
							 follow_updates, &buffer, tmfd);

	if (result == TM_Updated &&
		(flags & TUPLE_LOCK_FLAG_FIND_LAST_VERSION))
	{
		ReleaseBuffer(buffer);
		/* Should not encounter speculative tuple on recheck */
		Assert(!HeapTupleHeaderIsSpeculative(tuple->t_data));

		if (!ItemPointerEquals(&tmfd->ctid, &tuple->t_self))
		{
			SnapshotData SnapshotDirty;
			TransactionId priorXmax;

			/* it was updated, so look at the updated version */
			*tid = tmfd->ctid;
			/* updated row should have xmin matching this xmax */
			priorXmax = tmfd->xmax;

			/* signal that a tuple later in the chain is getting locked */
			tmfd->traversed = true;

			/*
			 * fetch target tuple
			 *
			 * Loop here to deal with updated or busy tuples
			 */
			InitDirtySnapshot(SnapshotDirty);
			for (;;)
			{
				if (ItemPointerIndicatesMovedPartitions(tid))
					ereport(ERROR,
							(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
							 errmsg("tuple to be locked was already moved to another partition due to concurrent update")));

				tuple->t_self = *tid;
				if (heap_fetch(relation, &SnapshotDirty, tuple, &buffer))
				{
					/*
					 * If xmin isn't what we're expecting, the slot must have
					 * been recycled and reused for an unrelated tuple.  This
					 * implies that the latest version of the row was deleted,
					 * so we need do nothing.  (Should be safe to examine xmin
					 * without getting buffer's content lock.  We assume
					 * reading a TransactionId to be atomic, and Xmin never
					 * changes in an existing tuple, except to invalid or
					 * frozen, and neither of those can match priorXmax.)
					 */
					if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple->t_data),
											 priorXmax))
					{
						ReleaseBuffer(buffer);
						return TM_Deleted;
					}

					/* otherwise xmin should not be dirty... */
					if (TransactionIdIsValid(SnapshotDirty.xmin))
						elog(ERROR, "t_xmin is uncommitted in tuple to be updated");

					/*
					 * If tuple is being updated by other transaction then we
					 * have to wait for its commit/abort, or die trying.
					 */
					if (TransactionIdIsValid(SnapshotDirty.xmax))
					{
						ReleaseBuffer(buffer);
						switch (wait_policy)
						{
							case LockWaitBlock:
								XactLockTableWait(SnapshotDirty.xmax,
												  relation, &tuple->t_self,
												  XLTW_FetchUpdated);
								break;
							case LockWaitSkip:
								if (!ConditionalXactLockTableWait(SnapshotDirty.xmax))
									/* skip instead of waiting */
									return TM_WouldBlock;
								break;
							case LockWaitError:
								if (!ConditionalXactLockTableWait(SnapshotDirty.xmax))
									ereport(ERROR,
											(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
											 errmsg("could not obtain lock on row in relation \"%s\"",
													RelationGetRelationName(relation))));
								break;
						}
						continue;	/* loop back to repeat heap_fetch */
					}

					/*
					 * If tuple was inserted by our own transaction, we have
					 * to check cmin against cid: cmin >= current CID means
					 * our command cannot see the tuple, so we should ignore
					 * it. Otherwise heap_lock_tuple() will throw an error,
					 * and so would any later attempt to update or delete the
					 * tuple.  (We need not check cmax because
					 * HeapTupleSatisfiesDirty will consider a tuple deleted
					 * by our transaction dead, regardless of cmax.)  We just
					 * checked that priorXmax == xmin, so we can test that
					 * variable instead of doing HeapTupleHeaderGetXmin again.
					 */
					if (TransactionIdIsCurrentTransactionId(priorXmax) &&
						HeapTupleHeaderGetCmin(tuple->t_data) >= cid)
					{
						ReleaseBuffer(buffer);
						return TM_Invisible;
					}

					/*
					 * This is a live tuple, so try to lock it again.
					 */
					ReleaseBuffer(buffer);
					goto tuple_lock_retry;
				}

				/*
				 * If the referenced slot was actually empty, the latest
				 * version of the row must have been deleted, so we need do
				 * nothing.
				 */
				if (tuple->t_data == NULL)
				{
					return TM_Deleted;
				}

				/*
				 * As above, if xmin isn't what we're expecting, do nothing.
				 */
				if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple->t_data),
										 priorXmax))
				{
					if (BufferIsValid(buffer))
						ReleaseBuffer(buffer);
					return TM_Deleted;
				}

				/*
				 * If we get here, the tuple was found but failed
				 * SnapshotDirty. Assuming the xmin is either a committed xact
				 * or our own xact (as it certainly should be if we're trying
				 * to modify the tuple), this must mean that the row was
				 * updated or deleted by either a committed xact or our own
				 * xact.  If it was deleted, we can ignore it; if it was
				 * updated then chain up to the next version and repeat the
				 * whole process.
				 *
				 * As above, it should be safe to examine xmax and t_ctid
				 * without the buffer content lock, because they can't be
				 * changing.
				 */
				if (ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid))
				{
					/* deleted, so forget about it */
					if (BufferIsValid(buffer))
						ReleaseBuffer(buffer);
					return TM_Deleted;
				}

				/* updated, so look at the updated row */
				*tid = tuple->t_data->t_ctid;
				/* updated row should have xmin matching this xmax */
				priorXmax = HeapTupleHeaderGetUpdateXid(tuple->t_data);
				if (BufferIsValid(buffer))
					ReleaseBuffer(buffer);
				/* loop back to fetch next in chain */
			}
		}
		else
		{
			/* tuple was deleted, so give up */
			return TM_Deleted;
		}
	}

	slot->tts_tableOid = RelationGetRelid(relation);
	tuple->t_tableOid = slot->tts_tableOid;

	/* store in slot, transferring existing pin */
	ExecStorePinnedBufferHeapTuple(tuple, slot, buffer);

	return result;
}


/* ------------------------------------------------------------------------
 * Definition of the heap table access method.
 * ------------------------------------------------------------------------
 */

static const TableAmRoutine heapam_methods = {
	.type = T_TableAmRoutine,

	.slot_callbacks = heapam_slot_callbacks,

	.scan_begin = heap_beginscan,
	.scan_end = heap_endscan,
	.scan_rescan = heap_rescan,
	.scan_getnextslot = heap_getnextslot,

	.parallelscan_estimate = table_block_parallelscan_estimate,
	.parallelscan_initialize = table_block_parallelscan_initialize,
	.parallelscan_reinitialize = table_block_parallelscan_reinitialize,

	.index_fetch_begin = heapam_index_fetch_begin,
	.index_fetch_reset = heapam_index_fetch_reset,
	.index_fetch_end = heapam_index_fetch_end,
	.index_fetch_tuple = heapam_index_fetch_tuple,

	.tuple_insert = heapam_tuple_insert,
	.tuple_insert_speculative = heapam_tuple_insert_speculative,
	.tuple_complete_speculative = heapam_tuple_complete_speculative,
	.tuple_delete = heapam_tuple_delete,
	.tuple_update = heapam_tuple_update,
	.tuple_lock = heapam_tuple_lock,

	.tuple_fetch_row_version = heapam_fetch_row_version,
	.tuple_get_latest_tid = heap_get_latest_tid,
	.tuple_satisfies_snapshot = heapam_tuple_satisfies_snapshot,
	.compute_xid_horizon_for_tuples = heap_compute_xid_horizon_for_tuples,
};


const TableAmRoutine *
GetHeapamTableAmRoutine(void)
{
	return &heapam_methods;
}

Datum
heap_tableam_handler(PG_FUNCTION_ARGS)
{
	PG_RETURN_POINTER(&heapam_methods);
}
