[Vertica][VJDBC](4700) ERROR: Sequence tablename_columnname_seq has not been accessed in the sessi

Firstly, I use hibernate and Vertica for the project, the identifier generate strategy is identity, and the program works fine. 
But after I configured the connection pool (tried both c0p3 and proxool), it shows below issue "Hibernate operation: could not retrieve generated id after insert, [Vertica][VJDBC](4700) ERROR: Sequence tablename_columnname_seq   has not been accessed in the session". 
In fact I'm using identity not sequence for the generation of the identifier, so not sure why the "[Vertica][VJDBC](4700) ERROR: Sequence tablename_columnname_seq   has not been accessed in the session" issue come out..

Anyone know something on this issue? Please kindly share you opioion..