PG vacuum Visibility

Two cases, one XMIN uncommitted transactions, xmin is a transaction has been submitted.
For xmin uncommitted transactions that just insert the current tuple has not been submitted to:
1) the tuple is not legitimate, ie bad tuple returned HEAPTUPLE_DEAD
2) The tuple is generated by the current transaction: At this point the transaction is not recorded in this or just delete locked or delete abort a delete it, then return HAPTUPLE_INSERT_IN_PROGRESS; if the record has been deleted, then returns HEAPTUPLE_DELETE_IN_PROGRESS
3) the tuple is generated by other transactions, tuple header mark uncommitted: HEAP_INSERT_IN_POGRESS
4) the tuple is generated other transactions, clog display xmin submitted: tuple is marked as head HEAP_XMIN_COMMITTED.
5) In other cases, this xmin transaction does not submit, abort or damaged: return HEAPTUPLE_DEAD
for the transaction xmin has been submitted, that the current tuple insert has been submitted:
1) Xmax did not submit returns HEAPTUPLE_LIVE
2) tuple only be locked with: xmax uncommitted: return HEAPTUPLE_LIVE
3) delete tuple is: return HEAPTUPLE_DELETE_IN_PROGRESS
4) clog found in xmax submitted: mark tuple head HEAP_XMAX_COMMITTED
5) other circumstances delete does not submit: HEAPTUPLE_LIVE
6) the rest of the case, tuple.t_xmax> = OldestXmin expressed Affairs also see the value of insert: HEAPTUPLE_RECENTLY_DEAD
7) other cases have been submitted XMAX: Return HEAPTUPLE_DEAD

HeapTupleSatisfiesVacuum
{
    HeapTupleHeader tuple = htup->t_data;

    if (!HeapTupleHeaderXminCommitted(tuple))//未提交
    {
        if (HeapTupleHeaderXminInvalid(tuple))//元组不合法，坏的元组
            return HEAPTUPLE_DEAD;
        else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
        {//当前事务产生的元组
            if (tuple->t_infomask & HEAP_XMAX_INVALID)//未被删除，当前事务正在insert
                return HEAPTUPLE_INSERT_IN_PROGRESS;
            //元组被锁住，未被删除 或者 
            if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) || HeapTupleHeaderIsOnlyLocked(tuple))
                return HEAPTUPLE_INSERT_IN_PROGRESS;
            //insert后当前事务又删除
            if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple)))
                return HEAPTUPLE_DELETE_IN_PROGRESS;
            //delete的子事务被abort，即insert正在进行
            return HEAPTUPLE_INSERT_IN_PROGRESS;
        }
        else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
        {//其他事务正在insert
            return HEAPTUPLE_INSERT_IN_PROGRESS;
        }//从clog中读取tuple的事务状态，为提交则标记提交
        else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
            SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,HeapTupleHeaderGetRawXmin(tuple));
        else
        {
            //真的tuple未提交、abort或者损坏
            SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,InvalidTransactionId);
            return HEAPTUPLE_DEAD;
        }
        //此时，xmin已提交了。
    }

    /*
     * Okay, the inserter committed, so it was good at some point.  Now what
     * about the deleting transaction?
     */
    if (tuple->t_infomask & HEAP_XMAX_INVALID)
        return HEAPTUPLE_LIVE;//未被删除则该记录是活的

    if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
    {//只是锁住，未进行delete
        if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
        {//delete事务未提交
            if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
                return HEAPTUPLE_LIVE;
            SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,InvalidTransactionId);

        }
        return HEAPTUPLE_LIVE;
    }
    //delete未提交
    if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
    {
        if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
            return HEAPTUPLE_DELETE_IN_PROGRESS;//delete正在进行
        else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))//从clog中检查delete提交了
            SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,HeapTupleHeaderGetRawXmax(tuple));
        else
        {
            //真的未提交、abort或者损坏
            SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,InvalidTransactionId);
            return HEAPTUPLE_LIVE;
        }
        //此时delete已提交
    }
    //有事务还可能看到他
    //tuple->t_choice.t_heap.t_xmax >= OldestXmin
    if (!TransactionIdPrecedes(HeapTupleHeaderGetRawXmax(tuple), OldestXmin))
        return HEAPTUPLE_RECENTLY_DEAD;
    /* Otherwise, it's dead and removable */
    return HEAPTUPLE_DEAD;
}