I am not a facebook fan neither an addict of it, but i still got to see “enq: FB contention”…thats bad :). Well this was for the first time i saw this wait event and it was on 11.2.0.2 version.Mostly, the enq: FB contention wait event was followed by log buffer space.
Well, the enq: FB contention is associated with block formatting and it ensures that only one process format the blocks in an ASSM tablespace.As i can think of, we had multiple sessions doing insert and could be that each session tried to format the block which caused the contention.The value on P1 is name|mode , P2 tells the tablespace number, and P3 gives the dba

[email protected] > select session_id,SQL_ID,EVENT,P1,P1text,P2,P3,WAIT_TIME,SESSION_STATE,TIME_WAITED from v$active_session_history where event like '%FB%';
SESSION_ID SQL_ID        EVENT                             P1 P1TEXT                P2         P3  WAIT_TIME SESSION TIME_WAITED
---------- ------------- ------------------------- ---------- ------------- ---------- ---------- ---------- ------- -----------
       775 bg65mx8g077g5 enq: FB - contention      1178730502 name|mode              9  285422249          0 WAITING      189987
      ......
      ......
[email protected] > select name from v$tablespace where ts#=9;
NAME
----------------------------------------
ABC_TBS_01
[email protected] > SELECT dbms_utility.data_block_address_block(285422249) "BLOCK",
           2  dbms_utility.data_block_address_file(285422249) "FILE"
           3  from dual;
     BLOCK       FILE
---------- ----------
    209577         68