Re: maximum # of connections per dispatcher

I think you mean the default maximum number of connections per dispatcher:
http://download-west.oracle.com/docs/cd/B10501_01/network.920/a96580/mts.htm#449895

I take it you've also considered
https://metalink.oracle.com/metalink/plsql/f?p=130:3:711126964612591896::::p3_database_id,p3_docid,p3_show_header,p3_show_help,p3_black_frame,p3_font:NOT,75712.1,1,1,1,helvetica more listeners.

I take it you think the dispatchers are busy by doing something similar to
https://metalink.oracle.com/metalink/plsql/f?p=130:3:711126964612591896::::p3_database_id,p3_docid,p3_show_header,p3_show_help,p3_black_frame,p3_font:NOT,1005259.6,1,1,1,helvetica ?

jg

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