Function RelationFindReplTupleSeq

src/backend/executor/execReplication.c:294–398

* Search the relation 'rel' for tuple using the sequential scan. * * If a matching tuple is found, lock it with lockmode, fill the slot with its * contents, and return true. Return false otherwise. * * Note that this stops on the first matching tuple. * * This can obviously be quite slow on tables that have more than few rows. */

 * This can obviously be quite slow on tables that have more than few rows.
 */
bool
RelationFindReplTupleSeq(Relation rel, LockTupleMode lockmode,
						 TupleTableSlot *searchslot, TupleTableSlot *outslot)
{
	TupleTableSlot *scanslot;
	TableScanDesc scan;
	SnapshotData snap;
	TypeCacheEntry **eq;
	TransactionId xwait;
	bool		found;
	TupleDesc	desc PG_USED_FOR_ASSERTS_ONLY = RelationGetDescr(rel);

	Assert(equalTupleDescs(desc, outslot->tts_tupleDescriptor, true));

	eq = palloc0(sizeof(*eq) * outslot->tts_tupleDescriptor->natts);

	/* Start a heap scan. */
	InitDirtySnapshot(snap);
	scan = table_beginscan(rel, &snap, 0, NULL);
	scanslot = table_slot_create(rel, NULL);

retry:
	found = false;

	table_rescan(scan, NULL);

	/* Try to find the tuple */
	while (table_scan_getnextslot(scan, ForwardScanDirection, scanslot))
	{
		if (!tuples_equal(scanslot, searchslot, eq))
			continue;

		found = true;
		ExecCopySlot(outslot, scanslot);

		xwait = TransactionIdIsValid(snap.xmin) ?
			snap.xmin : snap.xmax;

		/*
		 * If the tuple is locked, wait for locking transaction to finish and
		 * retry.
		 */
		if (TransactionIdIsValid(xwait))
		{
			XactLockTableWait(xwait, NULL, NULL, XLTW_None);
			goto retry;
		}

		/* Found our tuple and it's not locked */
		break;
	}

	/* Found tuple, try to lock it in the lockmode. */
	if (found)
	{
		TM_FailureData tmfd;
		TM_Result	res;