Multiple transactions can access and edit the same data concurrently with MVCC (Multi-Version Concurrency Control), a database management technique that preserves the data's integrity.
As data is changed over time, MVCC operates by producing and storing numerous versions of that data. This can increase concurrency and performance since it enables transactions to read and write data without the need for excessive locks.
When using an MVCC database, there are additional factors to take into account, such as increased storage needs and the possible burden of keeping different copies of the data.
In this blog post, we will delve into the details of how MVCC works, the benefits of using an MVCC database, and the considerations to keep in mind when deciding if an MVCC database is the right choice for your use case.
How MVCC Works
Each piece of data is kept in many versions by MVCC as it is changed over time. Each version of the data has a timestamp attached to it that shows when it was created.
A "snapshot" timestamp is specified by a transaction when it wishes to read data from an MVCC database. The database then gives the most recent iteration of the data as of the snapshot timestamp. This can also be known as time traveling queries when the snapshot time is in the past
A new version of the data with a new timestamp is created whenever a transaction wants to write data to an MVCC database. The previous version of the data is tagged as "inactive" and is no longer accessible to transactions using more recent snapshot timestamps, but it is not changed or erased.
To maintain the integrity of the data, transactions that write data to the database are executed independently of one another. Transactions and locks are used to accomplish this.
Several reads and writes are combined into a single logical operation using transactions. Multiple transactions cannot edit the same piece of data at the same time when locks are in place. Locks are often employed in an MVCC database merely to ensure the data's integrity, not to boost performance.
That's a brief overview of how MVCC works. In the next section, we will delve into the benefits of using an MVCC database.
Benefits of Using MVCC
- Concurrency and performance improvements are among the key advantages of using an MVCC database. MVCC can dramatically minimise the overhead associated with managing concurrency since it enables several transactions to access and alter data concurrently without the need for locks. As a result, the database may see better read and write rates and higher total throughput.
- Less locks and latches are required. In a conventional database, locks and latches are employed to safeguard the data's integrity and avoid conflicts. However, these processes can be resource-intensive and lead to bottlenecks that reduce the database's performance. Locks and latches are far less necessary with MVCC, which helps enhance database speed.
- Greater flexibility in addressing conflicts. MVCC eliminates the requirement for locks by allowing many transactions to edit the same data concurrently. When transactions attempt to edit the same data at the same time, conflicts may emerge. This may make them easier to resolve. Conflicts are often resolved in an MVCC database by rolling back one transaction and allowing the other to go through.
- Ability to quickly recover from failed or rolled-back transactions. Because MVCC databases isolate their transactions from one another, a failed or rolled-back transaction won't have an impact on the data that has already been modified by other transactions. As a result, it is simpler to verify data integrity and recover from transaction errors.
Considerations When Using an MVCC
- Higher storage needs. The increased storage needs are one of the primary factors to take into account when using an MVCC database. MVCC uses more storage than a conventional database since it saves several versions of each item of data. This may be a problem if there isn't much storage available or if there's a lot of data to store.
- Increased storage needs are not the only issue; there is also the potential cost associated with maintaining several versions of the same piece of information. This can include the effort and resources needed to produce and maintain the many data versions. The typical way of managing this is through a Garbage Collection Process
- MVCC can be more challenging to set up and maintain than a standard database due to its complexity. For developers and database managers who are unfamiliar with this sort of database, there may be a learning curve because it necessitates a new approach to managing concurrency and transactions. CockroachDB uses MVCC but has simplified the management of this for the developer and DBA. You can read more on CockroachDB on their website
In this article, we looked at the idea of MVCC (Multi-Version Concurrency Control), as well as the advantages and drawbacks of using an MVCC database.
The key advantages of implementing MVCC include
- Enhanced concurrency and throughput
- Decreased need for locks and latches
- Increased flexibility in addressing conflicts,
- Simple recovery from failed or rolled back transactions.
The considerations being
- Increased storage needs
- The possible burden of keeping several versions of data
- The difficulty of setting up and managing MVCC
These are a few things to take into account while adopting MVCC.
Weighing the benefits and drawbacks, as well as taking your application's particular needs and limitations into account, are crucial steps in determining whether an MVCC database is the best option for your use case.