Oracle DBA Checklist

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Step by Step: How to troubleshoot a slow running query in Oracle

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This is a day to day task of a DBA. Someone from application team comes to our desk and simply says a query is running slow. We may question him on many things but ultimately a DBA has to tune the query at the end. This is also very popular and known question for the DBA's who are attending interviews. This question is simply asked again and again. I have also been asked this question multiple times. After a pause, interviewer simply asks...so suppose a user comes and reports that his query is running slow, what will be your approach to tune this. There is no absolute or concrete answer to this question because there might be multiple way to tune a slow running query. Everyone can have a different approach. So here is my approach: Very first thing we have to find which type of query is running slow. Whether it is SELECT query of DML statements(insert, update, delete and merge). So first we will see how to tune a SELECT query Step 1 – Find the SQL_ID of the ...
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Register Archive log file manually in standby Database

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  Some time, the archive logs are not shipping to standby location due to network issue.  There may be  several  archive logs are waiting in standby location for one archive log file. For instance, Archive log sequence # 100 is not shipped to standby location. But other archive logs(sequence#101 to sequence#200) were shipped to standby and it is waiting to ship the sequence# 100.  In this scenario, DBA can copy the archive log file and register manually. Once manually registered, the sequence#101 to sequence#200 will apply automatically on standby database. Step 1 Let us assume, the archive log file devdb12_1_283_801988635.arc is not shipped to standby due to some reason. Copy the archive log file devdb12_1_283_801988635.arc manually from primary to standby archive destination location. Step  2 Run the below command in standby database. ALTER DATABASE REGISTER LOGFILE '/dbArch/oradata/devdb12/ devdb12_1_283_801988635.arc';   Step  3 Verify th...
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How to check UNDO tablespace usage and who is using more undo

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Query To check UNDO tablespace usage: ================================ set linesize 152 col tablespace_name for a20 col status for a10 select tablespace_name,status,count(extent_id) "Extent Count", sum(blocks) "Total Blocks",sum(bytes)/(1024*1024*1024) spaceInGB from   dba_undo_extents group by  tablespace_name, status having tablespace_name=upper('&TSNAME') order by tablespace_name; Query To check who is using more UNDO space: ===================================== SET termout ON SET heading ON SET PAGESIZE   6000 SET LINESIZE   200 COLUMN pgm_notes    FORMAT a80        HEADING 'Notes' COLUMN rbs          FORMAT a16         HEADING 'RBS'             JUST center COLUMN oracle_user  FORMAT a12        HEADING 'Oracle|Username' COLUMN sid_serial   FORMAT a12      ...
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