I’m refreshing our Hands-On Lab for Oracle Database 18c. And as part of a performance evaluation I wanted to set an underscore parameter to ignore all hints my load test tool sets. But then I learned: This does not work anymore as
_optimizer_ignore_hints is now
optimizer_ignore_hints. We made the underscore obsolete in Oracle Database 18c.
_optimizer_ignore_hints is now optimizer_ignore_hints
Actually in Oracle Database 126.96.36.199 you can find a long list of obsolete parameters here:
To be precise: We obsoleted159 parameters. In addition, in Oracle Database 18c we added an additional 8 parameters to the list. And just by coincidence I learned that
_optimizer_ignore_hints is one of them. But luckily it didn’t get removed but turned into a regular parameter. Which means: It is now documented as well.
This is how I learned about the change:
SQL> alter system set "_optimizer_ignore_hints"=true; alter system set "_optimizer_ignore_hints"=true * ERROR at line 1: ORA-25138: _OPTIMIZER_IGNORE_HINTS initialization parameter has been made obsolete
And this works now in Oracle Database 18c:
SQL> alter system set optimizer_ignore_hints=true; alter system set "_optimizer_ignore_hints"=true System altered.
In addition, we introduce optimizer_ignore_parallel_hints which gives you even more control.
Obsolete Parameters in Oracle Database 18c
In addition to the 159 parameters we made obsolete with Oracle Database 188.8.131.52, we obsoleted the following ones in Oracle Database 18c:
_bloom_use_crchash _key_vector_caching _log_event_queues _optimizer_ignore_hints _post_wait_queues_dynamic_queues _px_reuse_server_group standby_archive_dest utl_file_dir