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I read that shared server mode allows dispatcher processes to use two new SGA sturctures : queues (request and response) and UGA (which is just PGA "flushed" in SGA)

So with a that, a single dispatcher can handle several client connections.

My issue is I saw an expression I don't understand : "virtual circuit". What does it do and where exactly is it positionned ?

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Its a shared memory(in SGA) used by dispatcher for client connection requests and responses.

In a shared server configuration, client user processes connect to a dispatcher. The dispatcher can support multiple client connections concurrently. Each client connection is bound to a virtual circuit, which is a piece of shared memory used by the dispatcher for client database connection requests and replies. The dispatcher places a virtual circuit on a common queue when a request arrives.

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Reference

In other words, its a memory where the actual request is stored and shared server can know what it has to serve by reading this memory. For example if a client sends a query lets say select * from emp, the dispatcher has to store it somewhere so that an idle shared server process can pick it up and process further. The somewhere is the virtual circuit.

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  • But... what's the difference between the virtual circuit and the request queue? – Dudoso Jul 26 '17 at 17:44
  • @Dudoso You'll have to be more precise the context in which that expression was seen.... When you read virtual circuit , it seems it's the same thing... Post another question directly or ask JSapkota about it in another comment – Jason Krs Jul 27 '17 at 9:26

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