FROM_VAL 

VARCHAR2(4) 

PCM lock initial state: NULL; S; X; SSX 

TO_VAL 

VARCHAR2(4) 

PCM lock initial state: NULL; S; X; SSX 

ACTION_VAL 

VARCHAR2(51) 

Description of lock conversions

• Lock buffers for read

• Lock buffers for write

• Make buffers CR (no write)

• Upgrade read lock to write

• Make buffers CR (write dirty buffers)

• Downgrade write lock to read (write dirty buffers)

• Write transaction table/undo blocks

• Transaction table/undo blocks (write dirty buffers)

• Make transaction table/undo blocks available share

• Rearm transaction table write mechanism

COUNTER 

NUMBER 

Number of times the lock operation executed