Friday 20 May 2016

A data block was corrupted in alert log on Exadata

The following excerpt in the alert log on one of instances on Exadata:
Mon May 16 08:22:08 2016
Errors in file /u01/app/oracle/diag/rdbms//4/trace/4_dbw0_103431.trc:
ORA-01186: file 4097 failed verification tests
ORA-01157: cannot identify/lock data file 4097 - see DBWR trace file
ORA-01110: data file 4097: '+DATA1'
Mon May 16 08:22:08 2016
File 4097 not verified due to error ORA-01157
Mon May 16 08:22:08 2016
Dictionary check complete
Mon May 16 08:22:08 2016
Errors in file /u01/app/oracle/diag/rdbms//4/trace/4_dbw0_103431.trc:
ORA-01186: file 4097 failed verification tests
ORA-01157: cannot identify/lock data file 4097 - see DBWR trace file
ORA-01110: data file 4097: '+DATA1'
Mon May 16 08:22:08 2016
File 4097 not verified due to error ORA-01157
Mon May 16 08:22:09 2016
Re-creating tempfile +DATA1 as +DATA1//TEMPFILE/temp.5375.911982129

While at first it looks somewhat dangerous, it is a minor issue and self-healing. First of all one have to know the database in question is a standby, and it is in open mode with log apply (so Active Data Guard option in use). The file 4097 has id just above the db_files parameter - which immediately indicates this is a temporary file and such files do not exist by default on standbys - hence the inability to identify the file.
Now look at the last line in the excerpt - recreation of the temporary file, which heals the problem.

Thus if one looks at the v$database_block_corruptions, there is nothing there. In dba_temp_files also one does not meet the re-created tempfile - while this is standby, it does not change sources for this view apparently, while the file is listed in the v$tempfile.

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