Locks and Concurrency are tricky words. Understand the real purpose of these mechanisms for better use of database.
SYSIBM catalog tables are base tables defined under this schema. There are many schemas defined in DB2. To your quick reading, I have given all the key points here.
Data access is much faster in Hashing compared to the index. Read the differences between Hashing and Index.
Performance areas in DB2 must to improve.