One way to do this should be to turn off the insight on the connection.  This looks like a query for code insight and as such should be on a separate connection, thus not affecting your query or switched off.  If its not on the insight thread, then its a bug and we will look into that.  In the meantime, switch off insight and see does that help.

Thanks

Barry

It seems SQL Developer's Code Insight and PL/SQL Parser are the primary callers of the SQL you mention:

select table_owner, table_name

from all_synonyms

where owner in (user,'PUBLIC')

  and synonym_name=:1

  and not exists

    (select user, object_name

     from user_objects

     where object_name=:2

       and object_type in ('TABLE','VIEW'))

When I ran this through SQL Tuning Advisor, it recommended gathering statistics on SYS.SYN$.  After that, rather than getting a wide range of query times between 0.6 to 0.08 seconds, it narrowed a bit into a 0.2 to 0.09 second range.  This is all on a laptop with Oracle 11.2.0.1.

You never say what you mean by "awful", but the more awful it is, the more the responsibility falls on your DBA to fix it.  Aside from stale statistics, you may wish to run SQL Tuning Advisor yourself and see what it says.

Regards,
Gary

SQL Developer Team

Is your RDBMS version 12.1? How long

select * from user_synonyms where synonym_name= 'POTATO';

does it take to run?

I'm not able to confirm your assertion that this dictionary query is fired before user query. It is triggered either by code insight, or semantic analysis info tip; both can be opted out.

Vadim's answer is best, but the following discussion from early 2013 comes close to the same conclusion:

Unusable cause very slow automatic query

The lesson, of course, for all is:  search first, ask questions later.  Those who cannot remember the past are condemned to repeat it, especially me!