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From "Mike Matrigali (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-662) during crash recovery of a drop table, on case insensitive files systems derby may delete wrong file
Date Sat, 29 Oct 2005 14:19:55 GMT
during crash recovery of a drop table, on case insensitive files systems derby may delete wrong

         Key: DERBY-662
         URL: http://issues.apache.org/jira/browse/DERBY-662
     Project: Derby
        Type: Bug
  Components: Store  
 Environment: jvm/os/filesystem where file names are case insensitive such that delete of
C2080.dat will remove c2080.dat if it exists.
    Reporter: Mike Matrigali
 Assigned to: Mike Matrigali 
    Priority: Blocker

Sometimes during redo the system will incorrectly remove the file associated
with a table.  The bug requires the following conditions to reproduce:
1) The OS/filesystem must be case insensitive such that a request to delete
   a file named C2080.dat would also remove c2080.dat.  This is true in
   windows default file systems, not true in unix/linux filesystems that
   I am aware of.
2) The system must be shutdown not in a clean manner, such that a subsequent
   access of the database causes a REDO recovery action of a drop table
   statement.  This means that a drop table statement must have happened
   since the last checkpoint in the log file.  Examples of things that cause
   checkpoints are:
   o clean shutdown from ij using the "exit" command
   o clean shutdown of database using the "shutdown=true" url
   o calling the checkpoint system procedure
   o generating enough log activity to cause a regularly scheduled checkpoint.
3) If the conglomerate number of the above described drop table is TABLE_1,
   then for a problem to occur there must also exist in the database a table
   such that it's HEX(TABLE_2) = TABLE_1
4) Either TABLE_2 must not be accessed during REDO prior to the REDO operation
   of the drop of TABLE_1 or there must be enough other table references during
   the REDO phase to push the caching of of the open of TABLE_2 out of cache.

If all of the above conditions are met then during REDO the system will
incorrectly delete TABLE_2 while trying to redo the drop of TABLE_1.
I will be adding the following test to reproduce the problem:
1) create 500 tables, need enough tables to insure that conglomerate number
   2080 (c820.dat) and 8320 (c2080.dat) exist.
2) checkpoint the database so that create does not happen during REDO
3) drop table with conglomerate number 2080, mapping to c820.dat.  It looks
   it up in the catalog in case conglomerate number assignment changes for
   some reason.
4) exit the database without a clean shudown, this is the default for test
   suites which run multiple tests in a single db - no clean shutdown is done.
   Since we only do a single drop since the last checkpoint, test will cause
   the drop during the subsequent REDO.
5) run next test program dropcrash2, which will cause redo of the drop.  At
   this point the bug will cause file c2080.dat to be incorrectly deleted and
   thus accesses to conglomerate 8320 will throw container does not exist
6) check the consistency of the database which will find the container does
   not exist error.

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