SQL Gone Bad

What to do when faulty SQL code corrupts your database

Mary Louise PowersTom Smull

Lehigh University

Lehigh University technical environment

All SCT Banner modules installed

All Self Service products installed

AIX/Unix, Oracle 9i

Luminis / Portal

What can go wrong?

Batch updates to the systemAn unnoticed semi-colon“Fixes” to the systemPeople make mistakes

When it does go wrong

SymptomsScope (what / where / how many)CausesPossible Solutions / ResourcesEffect repairsCommunicate / DocumentPunish Offenders

What tools are available?

Most recent backupLast night’s exportLogMinerFlashback

LogMiner

Allows DBA to examine contents of archived redo logs Especially: SQL_REDO, SQL_UNDOKnowing when the error occurred is helpfulKnowing Oracle user who did it is also helpful

LogMiner script generation

Need access to current data dictionaryWhich archive logs are to be searched?Which tables are suspect?Which user performed the erroneous update?

accept start_seq prompt 'Starting sequence: 'accept end_seq prompt ' Ending sequence: '

spool logminer_&start_seq

select '-- exec dbms_logmnr_d.build(''ban6dictfile'',''/home/local/dba/logmnr'');'from sys.dual;

select 'exec dbms_logmnr.add_logfile(LogFileName=>'''||name||''',Options=>dbms_logmnr.NEW);'from V_$ARCHIVED_LOGwhere SEQUENCE# = to_number('&start_seq');

select 'exec dbms_logmnr.add_logfile(LogFileName=>'''||name||''',Options=>dbms_logmnr.ADDFILE);'from V_$ARCHIVED_LOGwhere SEQUENCE# between (to_number('&start_seq') +1) and (to_number('&end_seq'))order by SEQUENCE#;

-- PART 2…

select 'exec dbms_logmnr.start_logmnr(DictFileName=>''/~/dba/logmnr/ban6dictfile'');'from sys.dual;

select 'spool LOGMNR.lst select to_char(timestamp,''YY-MM-DD HH24:MI:SS'') DATE_TIME, username, sql_redo /* your code goes here */ from sys.v_$logmnr_contents /* where seg_name IN (''SPBPERS''); */ spool off exec dbms_logmnr.end_logmnr;'from sys.dual;

spool off

sys.v_$logmnr_contents (partial) Name Type ------------------------------- -------------- SCN NUMBER CSCN NUMBER TIMESTAMP DATE COMMIT_TIMESTAMP DATE THREAD# NUMBER LOG_ID NUMBER . SEG_OWNER VARCHAR2(32) SEG_NAME VARCHAR2(256) SEG_TYPE_NAME VARCHAR2(32) ROW_ID VARCHAR2(19) SESSION# NUMBER SERIAL# NUMBER USERNAME VARCHAR2(30) OPERATION VARCHAR2(32) OPERATION_CODE NUMBER SQL_REDO VARCHAR2(4000) SQL_UNDO VARCHAR2(4000) . SQL_COLUMN_TYPE VARCHAR2(32) SQL_COLUMN_NAME VARCHAR2(32)

-- exec dbms_logmnr_d.build('ban6dictfile','/home/local/dba/logmnr');exec dbms_logmnr.add_logfile(LogFileName=>'/u5/ORACLE/arch_ban6_1_136253.dbf', Options=>dbms_logmnr.NEW);exec dbms_logmnr.add_logfile(LogFileName=>'/u5/ORACLE/arch_ban6_1_136254.dbf', Options=>dbms_logmnr.ADDFILE);exec dbms_logmnr.add_logfile(LogFileName=>'/u5/ORACLE/arch_ban6_1_136255.dbf', Options=>dbms_logmnr.ADDFILE);exec dbms_logmnr.add_logfile(LogFileName=>'/u5/ORACLE/arch_ban6_1_136256.dbf', Options=>dbms_logmnr.ADDFILE);exec dbms_logmnr.add_logfile(LogFileName=>'/u5/ORACLE/arch_ban6_1_136257.dbf', Options=>dbms_logmnr.ADDFILE);exec dbms_logmnr.start_logmnr(DictFileName=>'/home/local/dba/logmnr/ban6dictfile');spool LOGMNR.lstselect to_char(timestamp,'YY-MM-DD HH24:MI:SS') DATE_TIME, username, sql_redo, sql_undofrom sys.v_$logmnr_contentswhere seg_name = 'SPBPERS'; and username = 'SATURN'spool offexec dbms_logmnr.end_logmnr;

-- FINAL GENERATED RECOVERY CODE:

update "SATURN"."SPBPERS" set "SPBPERS_ETHN_CODE" = 'H' where "SPBPERS_ETHN_CODE" IS NULL and ROWID = 'AAAGIeAADAABX+KAA';

update "SATURN"."SPBPERS" set "SPBPERS_ETHN_CODE" = 'X' where "SPBPERS_ETHN_CODE" IS NULL and ROWID = 'AAAGIeAADAABX+KAA';

update "SATURN"."SPBPERS" set "SPBPERS_ETHN_CODE" = 'W' where "SPBPERS_ETHN_CODE" IS NULL and ROWID = 'AAAGIeAADAABX+KAA';

update "SATURN"."SPBPERS" set "SPBPERS_ETHN_CODE" = 'H' where "SPBPERS_ETHN_CODE" IS NULL and ROWID = 'AAAGIeAADAABX+KAB';

Oracle Flashback

Lets you see data as it was in the past

Allows online processingNeed to know what was changedCan only go back as far as Undo Retention time Can restore accidental drop/deleteUseful to reset tables in testing mode

Requirements/Limitations

Oracle 9i or higherMust use Auto Undo ManagementLimited to undo retention timeUser must have certain privileges

Flashback any/target tableExecute on dbms_flashback

Flashback vs LogMiner

Logminer lets you review transactions to see what happened. Flashback requires you to know what happened.Flashback is limited to the retention time –

Logminer is limited by archivelog availability.Flashback can provide a before/after view of data in real time.

Flashback Query – Oracle9i

Dbms_flashback packageexec dbms_flashback.enable_at_time(…);select * from mytable;Exec dbms_flashback.disable;

declare Type pers_cursor is REF CURSOR; pcur pers_cursor; prow spbpers%ROWTYPE; BEGIN -- make sure no transactions or flashback in progress commit; dbms_flashback.disable;

-- set the database back to previous time dbms_flashback.enable_at_time(to_timestamp ('16-NOV-2005', 'DD-MON-YY')); open pcur for 'select * from spbpers where spbpers_ethn_code is not null'; -- move back to present by disabling flashback. dbms_flashback.disable; LOOP fetch pcur into prow; exit when pcur%NOTFOUND; update spbpers set spbpers_ethn_code = prow.spbpers_ethn_code where spbpers_pidm = prow.spbpers_pidm and spbpers_ethn_code is null; commit; END LOOP; END;

Flashback Query – Oracle9i

“as of” clauseSelect * from mytable as of timestamp ‘…’;

Example:

-- Restore rows erroneously deleted: insert into mytable (select * from mytable as of timestamp systimestamp - interval '15'

minute minus select * from mytable);

Flashback Enhancements - 10g

Flashback tableFlashback databaseVersion(s) query

Flashback Table

Alternative to point in time recovery from backup.Restores table to earlier point in time or “undrops” table.Requires select, insert, delete, alter, and flashback privileges on table.To “rewind” table, enable row movement.Flashback table <tablename> to timestamp.Recycle bin holds dropped tables.

Flashback table to earlierpoint in time

alter table mytable enable row movement;

flashback table mytable to SCN <scn#>;

Orflashback table mytable to TIMESTAMP ‘<timestamp>’;

Flashback Dropped Table FLASHBACK TABLE TO BEFORE DROP ORIGINAL NAME RECYCLEBIN NAME DROP TIME------------------- ------------------------------------------------------ ----------------------------NAME_ADDR BIN$6u0c1Kv2wG7gM4C0PwLAbg==$0 2004-12-10:19:25:47NAME_ADDR BIN$6R5+rrqmwPbgM4C0PwLA9g==$0 2004-11-17:19:30:19MYTABLE BIN$BdpRTDoogGrgQ4C0PwKAag==$0 2005-11-18:11:20:36

SQL> select * from "BIN$BdpRTDoogGrgQ4C0PwKAag==$0"; ID NAME---------- ----------------------------------- 1 Smull 2 Winwood 3 SmithSQL> flashback table "BIN$BdpRTDoogGrgQ4C0PwKAag==$0" to before drop;Flashback complete.

SQL> select * from mytable; ID NAME---------- ----------------------------------- 1 Smull 2 Winwood 3 Smith

Managing These Tools

Production vs Test SystemsAudit TrailsTemplates

References

Oracle Database Backup and Recovery Advanced User's Guide Oracle Database Backup and Recovery Basics Oracle Database Recovery Manager Reference

Questions?

Presenters

Mary Louise Powersmlp5@lehigh.edu

Tom Smulltjs5@lehigh.edu