Accomplishments:

The Recovery Manager is dependent on several other subsystems for its proper functioning. Our implementation of the algorithm would be of little use if it could not be appropriately tested. We thus had to build simple prototypes of all other subsystems we were interacting with - i.e. a Log Manager, Buffer Manager, Space Manager and the Transaction Manager. We also had to design a suitable testing tool - preferably one where tests were not hard coded and one which was easy to manipulate. The Log and Space Managers are built on top of UNIX files. Our Buffer Manager is an 'in-memory' data structure which uses the clock replacement algorithm for page replacement. We also built a parser that accepts commands to perform various actions on the system. The parser accepts the following commands:

T1 tbegin & T1 commit : Begin and Commit transaction T1.
T1 write <pgid> <offset> <data> & T1 read <pgid> <offset> : Write to and Read from a specified page at a specified offset.
T1 abort : Abort transaction T1.
tprint & dprint : Print current transaction table, dirty page table.
pgflush <pgid> & bflush : Flush the specified page to disk, flush the buffer pool to disk.
checkpoint : Take a checkpoint.
restart & restart_crash <crash point> : Restart the system , Restart the system but crash at a specified point.
crash : Crash the system.
texit : A clean exit.

The parser's driver executes appropriate routines on recognizing the command. We simulate multi-process execution by starting several transactions. Each transaction may be assumed to belong to a different process. In effect, the input to the system is a low level schedule of database actions. The next task was to build the Recovery Manager. As the other subsystems were ready, our task was limited to getting the algorithm right. To a good extent the pseudo-code in [MHL+90] helped us with the coding. There were several changes as we did not implement partial rollbacks or savepoints.

Next: Testing: Up: MINIREL : Recovery Manager

Previous: Internal Data Structures

ranjani ramamurthy
Sat May 13 16:56:49 CDT 1995