We have seen instances of the CDC agent taking an excessive amount of time to start.

On startup the agent issues the following query

select distinct c.column_name from ALL_LOG_GROUP_COLUMNS c, ALL_LOG_GROUPS g where c.owner = g.owner and c.log_group_name=g.log_group_name and c.table_name=g.table_name and g.always='ALWAYS' and c.owner='....' and c.table_name = '.....' order by 1;

This query uses the sys.USER$. sys.CON$ and sys.DEF$ tables. Adding statistics to these tables dramatically decreased the execution time of the query and meant the agent started in a more timely manner.