Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to dblink 53 0.00 0.00
SQL*Net message from dblink 53 0.13 6.29
In this case, the query is very simple??”it selects the next value of the sequence from the DUAL
table. But the sequence is remote (as seen in the execution plan), so the time required to fetch the
values is 6.29 seconds for 53 rows, out of a total of 6.5 seconds. To tune the application, you
either need to reduce the number of trips (such as by performing batch operations instead of rowby-
row operations) or eliminate the remote architecture component of the insert. If the remote
object (the sequence) and the local object (the DUAL table) can reside on the same database, the
wait times associated with the remote operations can be eliminated.
634 Oracle Database 11g DBA Handbook
NOTE
As of Oracle Database 10g, the DUAL table is an internal table, not a
physical table, and therefore does not generate consistent gets as long
as you don??™t use * as the column list in a query referencing DUAL.
Two problems commonly arise with replicated solutions: First, the local data may become out
of sync with the remote data. This is a standard problem with derived data; it limits the usefulness
of this option to tables whose data is fairly static. Even if a simple materialized view is used with a
materialized view log, the data will not be refreshed continuously??”only when scheduled.
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