PostgreSQL和MySQL的全面比較

介紹

讓我們快速了解 PostgreSQL 和 MySQL。這兩者都是重要的開源關係型資料庫管理系統，廣泛應用於不同的應用程式。

技術架構與設計理念

起源與發展

PostgreSQL 起源於 1986 年伯克利的 POSTGRES 項目，旨在透過嚴謹的學術研究和嚴格的 SQL 標準來推進資料庫管理系統。這項背景為 PostgreSQL 提供了專注於資料一致性的堅實理論基礎，使其成為複雜查詢和進階資料類型的理想選擇。其設計強調長期穩定性、可擴展性和社區驅動的創新。

相較之下，MySQL 由 Michael Widenius 和 David Axmark 創建於 1995 年，優先考慮實用性和易用性，以滿足快速發展的互聯網應用的需求。它簡化了資料庫管理並提高了效能，在網路繁榮時期迅速成為 Web 開發人員的首選。 MySQL 的重點始終是效能和易於部署。

資料庫引擎

MySQL的顯著特點是支援多種資料庫引擎，讓使用者可以根據自己的需求選擇最佳的儲存方式。從5.5版本開始，InnoDB一直是預設引擎，支援交易和行級鎖定，以實現高並發和資料一致性。 MyISAM雖然提供了更好的讀取效能，但缺乏事務支持，適合讀密集型場景。 MySQL 也為特定用例提供了 Memory 和 Archive 等引擎。

相較之下，PostgreSQL 使用統一的核心引擎，確保所有功能的一致性和互通性。此設計支援複雜查詢、事務管理和進階資料類型，同時簡化維護。儘管在某些情況下不如 MySQL 靈活，但 PostgreSQL 的內部靈活性和可擴展性透過分區和查詢最佳化等功能得到了增強。

比較 SQL 語法和功能

比較分析揭示了數組類型支援、JSON 處理、事務管理、臨時表、視窗函數、遞歸查詢、資料類型豐富性、預設值約束和區分大小寫等方面的差異和相似之處：

SQL Syntax/Feature	PostgreSQL	MySQL	Description
Array Types	Supported	Not directly supported	PostgreSQL allows direct definition of array type fields. MySQL simulates arrays using strings or other indirect methods.
JSON Support	Powerful	More basic	PostgreSQL has advanced JSON support with indexing and optimized queries. MySQL’s JSON support has improved in recent versions but remains simpler.
Transaction Handling	Fully ACID	Default auto-commit	PostgreSQL pulls off full ACID compliance by default, ideal for high-consistency scenarios. MySQL defaults to auto-commit for each statement but can be configured for transaction handling.
Temporary Tables	Session/Global Scope	Session Only	PostgreSQL allows both session-level and global temporary tables, while MySQL supports only session-level ones.
Window Functions	Supported	Supported since later versions	PostgreSQL has long supported window functions; MySQL added full support in more recent versions.
CTE (Common Table Expressions)	Supported	Supported	Both support CTE, but advanced usages or performance may vary.
Recursive Queries	Supported	Supported since version 8.0	PostgreSQL has supported recursive queries for a while, while MySQL started in version 8.0.
Data Types	More varied (like ARRAY, HSTORE, GIS types)	Basic types are comprehensive	PostgreSQL supports more specialized data types, while MySQL has a good set of basic types but not as diverse as PostgreSQL.
Default Value Constraints	Supports any expression	Has many limitations	PostgreSQL allows defaults to be any expression, whereas MySQL’s defaults are usually constants.
Case Sensitivity	Configurable	Defaults to case-insensitive	PostgreSQL can configure case sensitivity at the database or column level, while MySQL defaults to case-insensitive unless using binary collation.

注意：隨著時間的推移，兩個系統都會不斷更新，特定功能的支援和效能可能會改變。選擇資料庫時最好查閱最新的官方文件或發行說明。

進階功能比較：資料類型與事務處理

Feature/Database	PostgreSQL	MySQL
Advanced Data Types	Supports arrays, JSONB, hstore, etc., for complex data structures.	Supports JSON (enhanced in newer versions), but doesn't natively support arrays or hstore, needing indirect methods.
Window Functions	Early support for window functions, suitable for a variety of complex data analytics scenarios.	Added window functions in newer versions, progressively improving functionality but might lag in maturity and community resources.
Transaction Isolation Levels	Supports READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE, fully compliant with SQL standards.	Also supports these four isolation levels, but defaults to REPEATABLE READ and implements them via different storage engines (like InnoDB).
MVCC Implementation	Strong MVCC mechanism maintains multiple versions for each row, allowing for lock-free reads to enhance concurrency.	InnoDB uses MVCC via Undo Logs to maintain transaction views, optimizing read and write concurrency with its own locking strategies.
Locking Mechanism	Supports row-level locking combined with multi-version concurrency control, reducing lock contention and improving concurrency efficiency.	InnoDB supports row-level locking; MyISAM and other engines use table locks. Row-level locking improves concurrency but can be influenced by locking strategies and transaction designs.

資料類型和功能特徵

• 進階資料類型：PostgreSQL 提供了更豐富的選項，如陣列、JSONB、hstore，使其適合複雜的資料處理。
• 視窗函數和分析查詢：PostgreSQL 早期已經支援這些，而 MySQL 在較新的版本中加入了它們。
• 事務處理和並發控制：比較它們的隔離等級、MVCC 實作和鎖定機制，顯示出關鍵差異。

效能和可擴展性比較

Feature/Database	PostgreSQL	MySQL
Benchmarking and Workload	- Excels in complex queries and joins, thanks to rich indexing types and an optimizer. - Good balance for write-heavy and mixed workloads.	- Performs excellently in read-heavy scenarios, especially simple SELECT queries. - InnoDB engine optimizes read speed and handles concurrency well.
Scalability Strategy	- Supports partitioning for large tables to optimize query performance. - Parallel querying enhances large data processing capabilities. - Connection pooling management boosts concurrent processing.	- Achieves scalability via third-party tools (like PgPool-II, Patroni) for high availability and extensibility. - Sharding is common for horizontally scaling, ideal for large data distribution. - Offers replication (master-slave), group replication for redundancy and separating reads and writes.
Horizontal Scalability	- Native support is limited but can implement complex distributed deployments with third-party tools. - Citus extension enables real distributed SQL processing.	- Has more mature sharding solutions and clustering technologies, making horizontal scalability more flexible, especially for large internet applications.

性能和可擴展性的深入比較

Feature/Database	PostgreSQL	MySQL
Benchmarking and Workload	- With a powerful query optimizer and various indexing types, excels in complex query handling and analysis. - Balanced reading and writing, suitable for applications needing high-performance writing and complex analysis. - Excels in read-heavy contexts, particularly in simple SELECT queries, suited for web browsing and content distribution scenarios. - Optimizes read performance through read-write separation and caching strategies.	- Specializes in read-heavy operations for simple SELECT queries, perfect for content management systems and e-commerce platforms, ensuring optimized reading performance. - MySQL supports InnoDB optimizations for read speed and concurrency handling.
Scalability Solutions	- Partitions support range, list, hash, and more, boosting large table query efficiency. - Automatically leverages multi-core CPUs for parallel querying, enhancing data retrieval speed. - 内置和第三方连接池管理优化资源使用和响应时间。 - Using extensions like Citus for distributed processing. - Sharding, either manual or automated, disperses storage and processes large datasets to improve read and write performance. - Replication mechanisms (master-slave, group) enhance data availability and reading scalability.	- InnoDB Cluster provides integrated high availability and scalability solutions that simplify cluster management.

性能和可擴展性

• 基準測試和工作負載：分析兩個系統在不同工作負載下的效能，提到 MySQL 在讀取密集型環境中的優勢以及 PostgreSQL 在複雜查詢中的效率。
• 可擴充性：討論它們的水平可擴展性能力：MySQL 的分片策略與 PostgreSQL 的連接池、分區和平行查詢功能。

安全性和合規性比較

Feature/Database	PostgreSQL	MySQL
User Permission Management	- Fine-grained permission control with role and privilege inheritance, making it easier to manage complex permission structures. - Supports row-level security (RLS) for custom access control rules. - Provides a detailed user and permissions management system, with controls down to the database and table level.	- Doesn't natively support row-level security but can implement it through application logic.
Encryption Features	- Supports SSL/TLS encrypted connections to secure data transmission. - Has field-level encryption plugins to enhance security when data is at rest. - Transparent Data Encryption (TDE) options can be implemented through third-party extensions.	- Built-in SSL/TLS support protects network communications. - InnoDB storage engine supports table space encryption to secure data files. - MySQL Enterprise Edition offers more advanced encryption options.
Compliance Certification	- Complies with multiple security standards, including FIPS 140-2 and Common Criteria. - Supports data protection regulations like GDPR, but specific compliance measures need to be tailored to the environment.	- Holds several international security certifications like PCI DSS and ISO 27001. - Supports SSL/TLS and TDE, aiding in compliance with regulations like HIPAA and GDPR. - MySQL Enterprise Edition provides enhanced auditing and security functions to strengthen compliance.

安全與合規性

• 使用者權限管理：PostgreSQL 擅長細微控制和行級安全性。 MySQL專注於應用層安全適配。
• 加密功能：兩者都支援 SSL/TLS，但 PostgreSQL 透過擴充和欄位層級加密的高階控制來包含 TDE 選項。
• 合規認證：兩個資料庫都遵守各種安全標準，但PostgreSQL擁有更廣泛的認可認證，而MySQL的企業版則增強了合規能力。

應用場景及選型建議

Database	Suitable Scenarios
PostgreSQL	- Data analytics and business intelligence: Strong capabilities for complex queries, window functions, and geospatial data processing. - High compliance industries like finance and healthcare: Robust security and compliance features. - Complex application development: Supports advanced data types and multi-version concurrency, ideal for transaction-heavy applications.
MySQL	- Web applications and startups: Lightweight, easy to deploy, rich community resources, quick development cycles. - Read-heavy services: Such as content management systems and e-commerce platforms with optimized read performance. - Cloud-native environments: Deep integration with various cloud providers, suited for quickly scalable internet services.

決策框架

Decision Factor	Considerations	PostgreSQL Tendency	MySQL Tendency
Data Scale and Complexity	Volume of data, query complexity	Large datasets, complex queries, multi-dimensional analysis	Small to medium datasets, simple queries
Transaction Processing Needs	Complexity and consistency of transactions	High-concurrency transactions, strict ACID requirements	Simple transaction handling, read/write separation scenarios
Budget and Costs	Software licensing, operational costs	Open-source and free, but may require more professional support	Open-source and low cloud service costs
Team Familiarity and Skills	Technical stack match, learning curve	Requires strong SQL skills, suited for experienced teams	Friendlier for beginners, lower learning curve

注意事項

選擇資料庫時，沒有一刀切的選擇。相反，專注於最適合您需求的內容。在權衡這些因素時，請考慮執行小規模概念驗證 (POC)，以測試特定工作負載下的資料庫效能，然後再做出最終決定。此外，這兩個資料庫系統都在不斷改進並引入新功能，因此了解最新發展對於做出明智的選擇至關重要。

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