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ExpectRollforward.html 12-18-2001 Bikle ----------------------- Using Expect to Manage Oracle Recovery A standby database may be in one of several states: -Read Only Mode -Manual Recovery Mode -Managed Recovery Mode -Activated Mode A good description of the first three states may be found here: http://www.cs.rose-hulman.edu/docs/oracle-817/server.817/a76995/standbyc.htm#29765 I bumped into a situation recently when I had trouble moving a standby database from Manual Recovery mode to Read Only mode. Actually, I had no trouble when I was 'at the helm' so to speak. I noticed that sometimes my standby database would complain that it needed more recovery when I tried to move it from Manual Recovery mode to Read Only mode. Any DBA who sees this situation knows what to do; he/she pushes the standby database through more recovery and then reattempts a move to Read Only mode. Scripting this reaction can be a bit tricky using an ordinary shell script. The Expect script language, however, is well suited for emulating this DBA behavior. We display some pseudo-code which helps explain the linked script below: # define a useful function: define proc attempt2open {} { issue command: ALTER DATABASE OPEN READ ONLY; if db opens, return "READONLY" if db indicates a need for recovery, return "NEEDSRECOVERY" else return nothing } main {} { connect to db using sqlplus issue command: SHUTDOWN ABORT issue command: STARTUP NOMOUNT issue command: ALTER DATABASE MOUNT STANDBY DATABASE; # At this point the db may be in one of 2 states: # NEEDSRECOVERY # UNKNOWN set dbstate="UNKNOWN" call attempt2open{} to attempt Read Only mode and also get dbstate while { $dbstate == "NEEDSRECOVERY" } { issue command: RECOVER STANDBY DATABASE wait for a log to get applied issue command: CANCEL call attempt2open{} to attempt Read Only mode and also get dbstate } My observation of the above logic reveals that most calls to attempt2open{} result in the standby database moving to Read Only mode. Usually I do not enter the while {} loop. I have found with repeated experiments that every time that I have entered while loop, it did an excellent job of recovering the database to a state where it could be opened in Read Only mode. One experiment I need to run is to find out how the logic will work on a broken Standby Database. An implementation of the above pseudo code in the Expect scripting language is linked below: mv2readOnlyMode-exp.txt An actual screen dump from the above script is linked below: mv2ReadOnlySD.txt Inspection of the above screen dump reveals that it did encounter the situation where the script did need to enter the while-loop and rollforward by one log to find a state suitable to open the database in Read Only mode. This page is just a trivial example. The Expect scripting language, however, has the ability to automate a wide variety of DBA behaviors for many different recovery scenarios.