Mihail Nikalayeu <mihailnikala...@gmail.com> wrote: > Also, I think I found an issue (or lost something during rebase): we > must preserve xmin,cmin during initial copy > to make sure that data is going to be visible by snapshots of > concurrent changes later: > > static void > reform_and_rewrite_tuple(......) > ..... > /*It is also crucial to stamp the new record with the exact same > xid and cid, > * because the tuple must be visible to the snapshot of the > applied concurrent > * change later. > */ > CommandId cid = HeapTupleHeaderGetRawCommandId(tuple->t_data); > TransactionId xid = HeapTupleHeaderGetXmin(tuple->t_data); > > heap_insert(NewHeap, copiedTuple, xid, cid, HEAP_INSERT_NO_LOGICAL, > NULL);
When posting version 12 of the patch [1] I raised a concern that the the MVCC safety is too expensive when it comes to logical decoding. Therefore, I abandoned the concept for now, and v13 [2] uses plain heap_insert(). Once we implement the MVCC safety, we simply rewrite the tuple like v12 did - that's the simplest way to preserve fields like xmin, cmin, ... [1] https://www.postgresql.org/message-id/178741.1743514291%40localhost [2] https://www.postgresql.org/message-id/97795.1744363522%40localhost -- Antonin Houska Web: https://www.cybertec-postgresql.com
