During bootstrap dump of ACID tables, let's consider the below sequence.
- Get lastReplId = last event ID logged.
- Current session (Thread-1), REPL DUMP -> Open txn (Txn1) - Event-10
- Another session (Thread-2), Open txn (Txn2) - Event-11
- Thread-2 -> Insert data (T1.D1) to ACID table. - Event-12
- Thread-2 -> Commit Txn (Txn2) - Event-13
- Thread-2 -> Drop table (T1) - Event-14
- Thread-1 -> Dump ACID tables based on current list of tables. So, T1 will be missing.
- Thread-1 -> Commit Txn (Txn1)
- REPL LOAD from bootstrap dump will skip T1.
- Incremental REPL DUMP will start from Event-10 and hence allocate write id for table T1 and drop table(T1) is idempotent. So, at target, exist entries in TXN_TO_WRITE_ID and NEXT_WRITE_ID metastore tables.
- Now, when we create another table at source with same name T1 and replicate, then it may lead to incorrect data for readers at target on T1.
Couple of proposals:
1. Make allocate write ID idempotent which is not possible as table doesn't exist and MM table import may lead to allocate write id before creating table. So, cannot differentiate these 2 cases.
2. Make Drop table event to drop entries from TXN_TO_WRITE_ID and NEXT_WRITE_ID tables irrespective of table exist or not at target.