Set - 4

Question 16 :

What is a logical backup?

Answer :

Logical backup involves reading a set of database records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup.


Question 17 :

Where can one get a list of all hidden Oracle parameters? (for DBA)

Answer :

Oracle initialization or INIT.ORA parameters with an underscore in front are hidden or unsupported parameters. One can get a list of all hidden parameters by executing this query:
select *
from SYS.X$KSPPI
where substr(KSPPINM,1,1) = '_';
The following query displays parameter names with their current value:
select a.ksppinm "Parameter", b.ksppstvl "Session Value", c.ksppstvl "Instance Value"
from x$ksppi a, x$ksppcv b, x$ksppsv c
where a.indx = b.indx and a.indx = c.indx
and substr(ksppinm,1,1)='_'
order by a.ksppinm;
Remember: Thou shall not play with undocumented parameters!


Question 18 :

What is a database EVENT and how does one set it? (for DBA)

Answer :

Oracle trace events are useful for debugging the Oracle database server. The following two examples are simply to demonstrate syntax. Refer to later notes on this page for an explanation of what these particular events do.
Either adding them to the INIT.ORA parameter file can activate events. E.g.
event='1401 trace name errorstack, level 12'
... or, by issuing an ALTER SESSION SET EVENTS command: E.g.
alter session set events '10046 trace name context forever, level 4';
The alter session method only affects the user's current session, whereas changes to the INIT.ORA file will affect all sessions once the database has been restarted.


Question 19 :

What is a Rollback segment entry ?

Answer :

It is the set of before image data blocks that contain rows that are modified by a transaction. Each Rollback Segment entry must be completed within one rollback segment. A single rollback segment can have multiple rollback segment entries.


Question 20 :

What database events can be set? (for DBA)

Answer :

The following events are frequently used by DBAs and Oracle Support to diagnose problems:
" 10046 trace name context forever, level 4 Trace SQL statements and show bind variables in trace output.
" 10046 trace name context forever, level 8 This shows wait events in the SQL trace files
" 10046 trace name context forever, level 12 This shows both bind variable names and wait events in the SQL trace files
" 1401 trace name errorstack, level 12 1401 trace name errorstack, level 4 1401 trace name processstate Dumps out trace information if an ORA-1401 "inserted value too large for column" error occurs. The 1401 can be replaced by any other Oracle Server error code that you want to trace.
" 60 trace name errorstack level 10 Show where in the code Oracle gets a deadlock (ORA-60), and may help to diagnose the problem.
The following lists of events are examples only. They might be version specific, so please call Oracle before using them:
" 10210 trace name context forever, level 10 10211 trace name context forever, level 10 10231 trace name context forever, level 10 These events prevent database block corruptions
" 10049 trace name context forever, level 2 Memory protect cursor
" 10210 trace name context forever, level 2 Data block check
" 10211 trace name context forever, level 2 Index block check
" 10235 trace name context forever, level 1 Memory heap check
" 10262 trace name context forever, level 300 Allow 300 bytes memory leak for connections
Note: You can use the Unix oerr command to get the description of an event. On Unix, you can type "oerr ora 10053" from the command prompt to get event details.