Database Recovery Schemes Quiz

To bring the database into the last consistent state, which existed prior to the failure.

Transaction failure: Transactions may fail because of incorrect input, deadlock, incorrect synchronization.

Transaction Log

ARIES Recovery Scheme

Shadow paging

Analysis, redo, undo

Dirty pages and active transactions at the time of crash

Fuzzy checkpointing

Transaction table and dirty page table

Logging data updates before the actual update is performed

Reverses effects of transactions that were active at the time of crash.

Applies necessary changes to bring database to a consistent state.

Both data updates and transaction commits

Unique Log Sequence Number (LSN) and previous LSN of the transaction.

Both begin_checkpoint and end_checkpoint records

Storing data values before and after modification

Transaction ID (TID), back pointer, next pointer, operation details

Immediate update writes modified data item directly to disk

Stores the modified version of a data item separately from the original

Temporarily store data items to be modified

Ensure recovery when in-place updates are used

Suspended transaction execution, writing modified data to disk, logging checkpoint record, resuming transaction execution

Redo or undo operations for transactions following the checkpoint record

Steal, no-steal, force, or no-force methods

Redoing a transaction in the commit table

No undo and no redo

Both an active table and a commit table

They are redone

Idempotent property

Ignored

It undoes all transactions during recovery

Undo possible for some transactions, redo possible for others

No undo and no redo for any transaction

For all transactions in the active table

They are flushed to disk before committing

Helps with managing concurrency control

To redo any changes that appear in the dirty page table

Starts from the end of the log and proceeds backward while performing appropriate undo

It allows transactions to commit only when all multiple nodes agree to commit individually

To ensure that a transaction commits only when all multiple nodes agree to commit individually

They are recovered under their own recovery protocol at each node

The transaction is aborted if any one of these nodes fails or cannot commit

Allows writing logs before changes are made to database pages

No-Steal/Force property

The purpose of the ARIES recovery scheme is to ensure that the database can be brought back to a consistent state after a failure, while preserving the ACID properties of transactions (Atomicity, Consistency, Isolation, Durability). It uses a combination of undo and redo operations, along with a write-ahead logging protocol, to achieve efficient and reliable recovery.

The types of failures that may cause a database to become unavailable for use include transaction failure (due to incorrect input, deadlock, incorrect synchronization), system failure (due to addressing error, application error, operating system fault, RAM failure, etc.), and media failure (such as disk head crash, power disruption, etc).

The purpose of a checkpointing process in the context of database recovery is to create a stable point in the transaction log and ensure that all modified data pages are written to disk. This allows the system to recover efficiently from a failure by reducing the amount of log records that need to be processed during the recovery phase.

The purpose of data caching in the context of database recovery is to improve system performance by temporarily storing frequently accessed data in memory. However, during recovery, it is important to ensure that the cached data is consistent with the disk-based data to avoid data loss or inconsistency.

The Write-Ahead Logging (WAL) protocol is used to ensure recovery when in-place updates are used, by writing the Before Image (BFIM) and After Image (AFIM) to the log.

The database cache is used to temporarily store data items to be modified; the cache manager controls flushing using modified and pin-unpin bits.

Transaction roll-back (undo) and roll-forward (redo) are used to maintain atomicity by restoring all Before Images (BFIM) or After Images (AFIM) to the database.

Checkpointing involves suspended transaction execution, writing modified data to the disk, logging the checkpoint record, and resuming transaction execution.

Immediate update method writes the modified data item directly to the disk, while deferred update method waits for the transaction to finish or a certain number of transactions to complete before writing the modified data item to the disk.

The transaction log consists of records, each with a transaction ID (TID), back pointer to the previous log record, next pointer to the next log record, and operation details.

Shadow update method stores the modified version of a data item separately from the original.

The Redo phase in the ARIES Recovery Algorithm is required to reapply changes from log records to the database during recovery.

The transaction log is a sequential file used for database recovery, storing data values before and after modification, as well as other relevant information.

Write-Ahead Logging (WAL) protocol is used to ensure recovery when in-place updates are used, by writing the Before Image (BFIM) and After Image (AFIM) to the log.

The database cache can be flushed to the disk using steal, no-steal, force, or no-force methods.

During recovery, redo or undo operations are required for transactions following the checkpoint record to ensure consistent database state.

The four different ways for handling recovery in database systems are: Steal/No-Force (Undo/Redo), Steal/Force (Undo/No-redo), No-Steal/No-Force (Redo/No-undo), and No-Steal/Force (Noundo/No-redo).

The Deferred Update recovery scheme involves No Undo/Redo.

In a single-user system, data update involves: 1) transactions recording updates in the log, 2) updates being saved on the database disk at commit point under the Write-Ahead Logging (WAL) scheme, 3) redoing all affected transactions using the log after a failure reboot, and 4) no undo being required due to no Anomalous Fatal Image (AFIM) being flushed to the disk before a transaction commits.

In a concurrent users system, deferred update recovery requires both an active table and a commit table. During recovery, all transactions in the commit table are redone, while all transactions in the active table are ignored.

The idempotent property of a redone transaction ensures its consistency in the commit table during recovery.

The Undo/No-redo Algorithm involves flushing Anomalous Fatal Image (AFIMs) of a transaction to the database disk under Write-Ahead Logging (WAL) before it commits.

In a single-user environment using the Undo/Redo Algorithm, the recovery manager undoes a transaction if it is in the active table and redoes a transaction if it is in the commit table.

The recovery manager performs undo and redo for recovery in a concurrent execution environment using the Undo/Redo Algorithm.

The Immediate Update recovery technique flushes Anomalous Fatal Image (AFIMs) to the database disk under Write-Ahead Logging (WAL) before a transaction commits, and the recovery manager undoes all transactions during recovery, with no redos.

The active table and the commit table are used in deferred update recovery for concurrent users to ensure that all transactions in the commit table are redone, while all transactions in the active table are ignored during recovery.

The No-Steal/Force (Noundo/No-redo) method of handling recovery means that no undo or redo is required for any transactions, as no Anomalous Fatal Image (AFIM) is flushed to the disk before a transaction commits.

The purpose of the recovery manager in a database system is to ensure the consistency and integrity of the database after a failure or crash, by performing undo and redo operations as necessary.

The ARIES recovery algorithm consists of two phases: the redo phase and the undo phase. The purpose of the redo phase is to reapply any changes that appear in the dirty page table, moving forward from the point in the log where all dirty pages have been flushed to the end of the log. The undo phase, on the other hand, starts from the end of the log and proceeds backward, performing appropriate undo operations and writing compensating records in the log for each undo.

In a multidatabase system, the 'two-phase commit' (2PC) ensures that a transaction commits only when all multiple nodes agree to commit individually the part of the transaction they were executing. If any one of these nodes fails or cannot commit, then the transaction is aborted.

The transaction log in database recovery records all the changes made to the database, allowing the system to redo committed transactions during the redo phase and undo uncommitted or aborted transactions during the undo phase. This helps maintain consistency by ensuring that all committed changes are applied and uncommitted changes are rolled back.

The dirty page table in the ARIES recovery algorithm keeps track of the pages in the buffer pool that have been modified but not yet written to disk. It is significant because the redo phase of the algorithm reapply any changes that appear in the dirty page table to ensure that all committed changes are applied to the database.

A multidatabase system is a special distributed database system where different nodes may run different types of database systems. Unlike a traditional distributed database system where all nodes run the same type of database system, a multidatabase system allows each node to run a different type of database system, such as relational or object-oriented.

In a distributed fashion at multiple nodes, a transaction commits only when all these multiple nodes agree to commit individually the part of the transaction they were executing. If any one of these nodes fails or cannot commit the part of the transaction, then the transaction is aborted. Each node recovers the transaction under its own recovery protocol.

The 'two-phase commit' (2PC) ensures that a transaction commits only when all multiple nodes agree to commit individually the part of the transaction they were executing in a distributed environment. If any one of these nodes fails or cannot commit, then the transaction is aborted.

The dirty page table keeps track of modified pages in the buffer pool, while the transaction log records all changes made to the database. During recovery, the dirty page table helps identify changes that need to be redone, while the transaction log helps identify changes that need to be undone, ensuring that the database remains consistent.

Checkpointing in the ARIES Recovery Algorithm serves the purpose of minimizing work for the recovery manager by committing transactions and keeping active transactions. This is achieved by writing begin_checkpoint and end_checkpoint records to the log, appending the transaction table and dirty page table to the log, and writing the LSN of the begin_checkpoint record to a special file.

The ARIES recovery algorithm consists of three steps: analysis, redo, and undo. Analysis identifies dirty pages and transactions active at the time of crash, and determines the appropriate log record for redo to start. Redo applies necessary changes to bring the database to a consistent state. Undo reverses the effects of transactions that were active at the time of crash.

In the ARIES Recovery Algorithm, Write Ahead Logging (WAL) ensures that log records are written for data updates, transaction commits, transaction aborts, undo, and transaction ends. Each log record has a unique Log Sequence Number (LSN) and stores the previous LSN of the transaction, transaction ID, and type of log record, which aids in efficient recovery.

Fuzzy checkpointing in the ARIES Recovery Algorithm is used to reduce the cost of checkpointing and allow the system to continue executing transactions. It involves writing any necessary log records to the log during recovery, as the system continues to execute transactions, thus reducing the overall overhead of the checkpointing process.

During checkpointing in the ARIES Recovery Algorithm, the transaction table and dirty page table are stored in the log, along with begin_checkpoint and end_checkpoint records, which are written to the log. Additionally, the LSN of the begin_checkpoint record is written to a special file for reference during recovery.

The AFIM and BFIM in ARIES Recovery Algorithm maintain shadow copies of data items, providing a method to manage access to data items by concurrent transactions using both current and shadow directories. These shadow copies play a crucial role in the recovery process, aiding in ensuring database consistency and integrity during recovery operations.

The Write Ahead Logging (WAL) protocol in the ARIES Recovery Algorithm ensures that log records are written before the corresponding data updates, transaction commits, transaction aborts, undo, and transaction ends are performed. This protocol helps maintain the integrity and consistency of the log, facilitating efficient recovery and ensuring durability of transactions.

During the analysis phase of the ARIES recovery algorithm, the system identifies dirty pages and transactions active at the time of crash. It also determines the appropriate log record for redo to start by analyzing the state of the database and the log, in order to bring the database to a consistent state during recovery.

Shadow paging is a method used in ARIES Recovery Algorithm to manage access to data items by concurrent transactions, using both current and shadow directories. It serves the purpose of maintaining data item consistency and integrity during concurrent access, and involves managing access to data items by maintaining both current and shadow directories, ensuring recoverability and consistency in the event of failures or crashes.

In the log records of ARIES Recovery Algorithm, each record has a unique Log Sequence Number (LSN) and stores the previous LSN of the transaction, transaction ID, and type of log record. These components play a crucial role in efficient recovery, providing necessary information for identifying and managing transactions and their corresponding log records during the recovery process.

The undo phase in the ARIES Recovery Algorithm reverses the effects of transactions that were active at the time of crash, ensuring consistency and integrity of the database. It plays a crucial role in rolling back the effects of incomplete or active transactions, and restoring the database to a consistent state during the recovery process.

The 'Write Ahead Logging (WAL)' in the ARIES Recovery Algorithm ensures that log records are written before the corresponding data updates, transaction commits, transaction aborts, undo, and transaction ends are performed. This protocol helps maintain the integrity and consistency of the log, facilitating efficient recovery and ensuring durability of transactions.