Question
how to Monitor Undo with SQL*Plus
Answers
Use SQL*Plus to monitor undo generation, long queries, and undo errors.
1. Connect to your instance with SQL*Plus as user SYSTEM.
2. Set up your session for displaying dates conveniently.
SQL> alter session set nls_date_format='dd-mm-yy:hh24:mi:ss';
3. Query V$UNDOSTAT as follows:
SQL> select begin_time, end_time, undoblks, maxquerylen, ssolderrcnt,
nospaceerrcnt from v$undostat;
4. Interpret the results of the query. Note that the view has one row per tenminute
interval, showing you how much undo was generated, in blocks; how
long the longest query was, in seconds; and whether there were any “snapshot
too old” errors, or errors from transactions running out of undo space.
5. Calculate the minimum necessary size in bytes for your undo tablespace that
will prevent errors, given your current activity data, with this query:
select
(select max(undoblks)/600 * max(maxquerylen) from v$undostat)
*
(select value from v$parameter where name='db_block_size')
from dual;   Your Comment




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