SQL*Net round trip tracing is a useful tool for helping determine or
eliminate possible sources of network latency. As the name
implies, a round trip is the number of trips required to satisfy a
request for data. An excessive number of round trips could
cause network performance issues. Many factors can
impact the number of round trips.
For example, ARRAYSIZE can impact network performance. The
ARRAYSIZE determines how much data can be returned in each round
trip; therefore, an ARRAYSIZE that is too small for the data
requested can force too many round trips. To optimized the
ratio of round trips, the
ARRAYSIZE can be adjusted.
Network buffers and packets can also impact the number of round
trips. While it's still true that tuning of network packet
traffic happens at the network level, it is also important that the
Oracle net
parameter be optimized as well.
The session data unit (SDU) and transport data unit (TDU) are
resident in the tnsnames.ora file and can have an impact on round
trips. The SDU determines the packet size to be sent over the
network while the TDU is the default packet size for grouping data
together. There are some important guidelines for
setting the SDU and TDU properly in the tnsnames.ora.
Also, see these notes for
Optimizing Oracle Net parameters.
The
SQL*Net more data to client wait event happens
when Oracle writes multiple data buffers (sized per SDU) in a single
logical network call; however, it is not a direct measure of network
latency.
In order to determine the appropriate settings, it will be helpful
to trace the SQL*Net round trips as empirical tests are conducted.
Tips on how to initiate SQL*Net traces from both the client and
server side are available
HERE.
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