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Don Burleson Blog 







Virtual Circuit wait tips

Oracle Database Tips by Donald BurlesonJanuary 10, 2015

Question:  I just upgraded from 10g to 11g and I now see poor performance.  My AWR report looks like this, with high Oracle virtual circuit wait events:

Top 5 Timed Foreground Events
Event                Waits  Time(s) Avg wait (ms) % DB time Wait Class
virtual circuit wait 95,038 16,056  169             263.91  Network

What is a virtual circuit, and why is my instance waiting on it?
Answer:  First check MOSC Note 1225943.1 titled High virtual circuit waits after upgrade.  A high "virtual circuit wait" wait event has two display parameters, P1 ("the circuit#") and P2 ("the type").

Parameter Description
circuit# Indicates the virtual circuit# being waited on
type Indicates the type of operation the session is waiting for

Beware, the virtual circuit wait has been associated with the use of shared servers (The multi-threaded server, or MTS).  Oracle DOES NOT recommend using shared servers, except as a stopgap measure because dedicated database connections are faster and  more resilient:

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