分两种情况，一是XMIN事务未提交，一个是xmin事务已提交。
针对xmin未提交的事务，即当前的tuple刚insert还未提交：
1）元组不合法，即坏元组时，返回HEAPTUPLE_DEAD
2）该tuple是当前事务产生的：此时这个记录在这个事务未删除或只是被锁住或进行了delete但是delete abort了，那返回HAPTUPLE_INSERT_IN_PROGRESS；若则记录又被删除了，那返回HEAPTUPLE_DELETE_IN_PROGRESS
3）该tuple是其他事务产生的，tuple头中标记未提交：HEAP_INSERT_IN_POGRESS
4）该tuple是其他事务产生，clog中显示xmin已提交：则标记tuple头为HEAP_XMIN_COMMITTED。
5）其他情况下，这个xmin事务确实未提交，abort或损坏了：返回HEAPTUPLE_DEAD
针对xmin已提交的事务，即当前的tuple insert已提交了：
1）xmax未提交，返回HEAPTUPLE_LIVE
2）tuple只是被锁着：xmax未提交：返回HEAPTUPLE_LIVE
3）tuple正在delete：返回HEAPTUPLE_DELETE_IN_PROGRESS
4）clog中查到xmax已提交：标记tuple头HEAP_XMAX_COMMITTED
5）其他情况delete确实未提交：HEAPTUPLE_LIVE
6）剩下的情况，tuple.t_xmax >= OldestXmin表示有事务还能看到insert的值：HEAPTUPLE_RECENTLY_DEAD
7）其他情况XMAX已提交了：返回HEAPTUPLE_DEAD
函数为：HeapTupleSatisfiesVacuum
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; }
