PostgreSQL is a wide known open-source advanced object-rational DBMS having many powerful features required for corporate data warehouses: asynchronous commit, both synchronous and asynchronous models of replications, different indexing options and many others. Nevertheless, a lot of companies including world biggest corporations like Uber migrate from PostgreSQL to MySQL. Most common reasons for migration are the following weaknesses of PostgreSQL:
- lackof multi-version concurrency control (MVCC)
- error prone upgrading to newer releases
- too complicated administration and development
The most crucial bottlenecks of PostgreSQL are explored below.
MVCC Support
Implementation of replica MVCC support in PostgreSQL implies some challenges. While the real replica MVCC support demands that replicas maintain an identical copy of the master’s on-disk data, in PostgreSQL replicas retain old row versions for MVCC.
When a streaming replica has an ongoing transaction, any modifications of the PostgreSQL database affecting rows held open by that transaction are blocked. As a result, the Write-Ahead Log (WAL) application thread is suspended until the transaction completes. This may lead to noticeable delays between the master and the replica, especially if the transaction takes a significant amount of time to finish. To address this issue, PostgreSQL incorporates a timeout mechanism. If a transaction causes the WAL application to be blocked for a specific duration, PostgreSQL terminates that transaction to prevent prolonged delays.
This design characteristic of PostgreSQL can result in occasional delays of a few seconds between replicas and the master. As a result, it becomes easier to inadvertently write code that leads to terminated transactions. Application developers, especially those who lack deep database expertise and rely on ORMs (Object-Relational Mappers) that abstract low-level details, may not be fully aware of this issue. For example, if a developer has code that sends an email receipt to a user, the code may implicitly keep a database transaction open until the email is sent. While it is generally considered best practice to avoid keeping database transactions open during unrelated blocking I/O operations, developers may not always be conscious of this, which can lead to potential problems.
It is crucial for developers to comprehend the implications of PostgreSQL’s replica MVCC support and its impact on transaction handling. By being aware of the potential issues and ensuring proper transaction management, developers can prevent unintended consequences and maintain the desired performance and data integrity in their applications.
How to Migrate from PostgreSQL to MySQL
When converting a database from PostgreSQL to MySQL, it’s important to consider the differences in SQL syntax, features, and behavior between the two database systems. Migrating complex queries, stored procedures, and functions from PostgreSQL to MySQL may require significant modifications to ensure compatibility. Therefore, careful planning and thorough testing are recommended for a successful migration.
Fortunately, there are specialized tools available to assist with the migration process. One such tool is the PostgreSQL to MySQL converter, which facilitates steps like schema migration, types mapping, conversion of indexes, constraints, views, and data migration. This converter utilizes low-level algorithms for reading and writing data, ensuring high performance without relying on ODBC or other middleware. Benchmarks indicate a migration speed of approximately 50,000 rows per second on a medium P5 two-core system.
Here are some notable features of the PostgreSQL to MySQL converter:
- Compatible with modern versions of both on-premises and cloud-based MySQL and PostgreSQL.
- Supports conversion of tables, types, data, indexes, and constraints.
- Offers command line support for scripting and scheduling the database conversion.
- Supports SSL connection for PostgreSQL.
- Provides the option to export the PostgreSQL database into a MySQL script file.
- Allows filtering of PostgreSQL data to be migrated using SELECT queries.
- Offers the option to merge or synchronize existing MySQL tables with PostgreSQL data.
To learn more about the PostgreSQL to MySQL converter and its capabilities, you can visit the official website of Intelligent Converters.