The technical practice and principles of the POJO MVCC framework in the Java class library
The technical practice and principles of the POJO MVCC framework in the Java class library
MVCC (multi -version concurrent control) is a method for implementing concurrent control in the database system. It is also widely used in the Java class library, especially in the POJO (simple old Java object) framework.This article will introduce the technical practice and principles of the POJO MVCC framework, and provide some Java code examples.
1. Introduction to POJO MVCC framework
In the POJO MVCC framework, multiple transactions can read and modify the data in the database at the same time without interference or cause data inconsistent.Each transaction has its own reading view. This view was created at the beginning of the transaction and was destroyed at the end of the transaction.Reading view allows transaction to read the consistency view of the database, not affected by other transactions.
2. Technical practice of the POJO MVCC framework
2.1 Reading viewing view
In the POJO MVCC framework, each transaction needs to maintain its reading view.Reading views can be implemented by saving the snapshots of the database, or using some other mechanisms to track the read -readable data.Reading views need to be supported and read, and can be continuously updated during the transaction period.
The following is a sample code to demonstrate how to realize the viewing view in the POJO MVCC framework:
public class ReadView {
private Map<String, Object> snapshot = new HashMap<>();
public void read(String key) {
snapshot.put(key, Database.get(key));
}
public Object get(String key) {
return snapshot.get(key);
}
}
2.2 Implementation of transaction isolation
Each transaction should be isolated during execution, that is, transactions are not affected by other transactions when reading data.It can be isolation of transaction through locking and version control.For example, when a transaction is required to modify the data, it needs to obtain a lock to ensure that other transactions cannot modify the same data at the same time.
The following is an example code to demonstrate how to achieve the isolation of transactions in the POJO MVCC framework:
public class Transaction {
private ReadView readView = new ReadView();
private WriteView writeView = new WriteView();
public void begin() {
writeView.begin();
}
public void read(String key) {
readView.read(key);
}
public void write(String key, Object value) {
writeView.write(key, value);
}
public void commit() {
writeView.commit();
}
}
public class WriteView {
private Map<String, Object> modifications = new HashMap<>();
public void begin() {
// Acquire locks
// Start a new version
}
public void write(String key, Object value) {
modifications.put(key, value);
}
public void commit() {
// Apply modifications
// Update versions
// Release locks
}
}
3. Principles of POJO MVCC framework
3.1 Efficient reading operation
The POJO MVCC framework should support efficient concurrent reading operations to improve system performance.Reading operations should try to avoid locking and blocking other transactions, but use reading views to ensure the consistency of reading.
3.2 Atomicity and consistency of transactions
The POJO MVCC framework should ensure the atomicity and consistency of transactions.Each transaction should either fully execute, roll back completely, and maintain data consistency during the execution of the transaction.
3.3 Missing fault tolerance and recovery mechanism
The POJO MVCC framework should have fault tolerance and recovery mechanism to deal with possible errors and faults.For example, a logging mechanism can be used to record the changes in transactions and versions in order to recover data after the system failure.
In summary, the POJO MVCC framework is an important technology that implements concurrent control in the Java library.Through practice and following some basic principles, high -performance, reliable and consistent database access frameworks can be constructed.
