Is this a bug?

[zzl221000]

I have a big table with 500 million data. Update the database with the following statement

A:
merge (n:rlnode ? ) merge (m:rlnode ?) merge (n)-[:knows ?]->(m);
B:
merge (n:rlnode %s ) merge (m:rlnode %s) merge (n)-[:knows %s]->(m);
A statement is executed after setting PGobject, it takes 5 minutes.
B statement is executed after splicing the string, in 5 milliseconds