The Environment Variable DB2_RR_TO_RS enables\disables the Repeatable Read attribute. I's enabled for DB2 performance  purposes 

DB2 registry parameter DB2_RR_TO_RS is used to:

• Set a default isolation level for user tables to Read Stability (RS) isolation level. The RS level is not dissimilar to the Repeatable Read (RR) , with one difference – a page or row retrieved remains locked to the UOW end , but if another application can insert a value , that will be read if your process access the row a second time .
• Reduce locking the next key for inserted or changed rows
• Reduce deadlocks when using reverse scan indexes (ALLOW REVERSE SCANS) . i.e performing a scan in the opposite direction it’s intended

This environment variable is now deprecated

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