Oracle Database Timezone Issue


Post changes in Linux system timezone (in /etc/sysconfig/clock file ) from ZONE="America/New York" to ZONE="Asia/Kolkata" systimetamp over the DB link or TNS alias started reflecting old/wrong timezone 

sqlplus <username>@<TNS_Alias>/<password>;

SQL> select systimestamp,current_timestamp from dual;

SYSTIMESTAMP                            CURRENT_TIMESTAMP
-----------------------------------     -------------------------------------------
22-05-13 06:11:17.900646 AM -05:30      22-05-13 05:11:17.900654 PM +05:30 

Here , +05:30 was the correct time-stamp for Timezone "Asia/Kolkata"


It was identified that time zone of the database server was not matching with one of the Data guard setup in Linux zone configuration file /etc/sysconfig/clock

Required ZONE="Asia/Kolkata" 
But found ZONE="America/New York"

statspack report hangs

Problem: Statspack report hangs 

Executing @?/rdbms/admin/spreport.sql report hangs in midway & unable to proceed further until cancelled

Even if we try to keep it for Hours after undo_retention limit it will throw "ORA-01555 snapshot too old" & come out

Such issue is observed in pre-10g databases where there is no other substitute to stats-pack & its due to huge db object count


Initial analysis,  i kept the report running for over night & it kicked me out with ORA-01555 error after 9 Hours

Further , PERFSTAT.STATS$SQL_SUMMARY table found to be the problem causing table which was doing "db file sequential read" infinitely