Database System Files
🧠 What Are Database System Files?
These are special files Oracle uses to manage and run the database. They are different from data files, which store actual user and application data.
🗄️ Essential Database System Files for Startup
| File Type | Description |
|---|---|
| Control files 📝 | Store metadata about data files and redo log files (names, status). Needed to open the database. Multiple copies recommended (multiplexing). Each CDB has one control file; PDBs do not have their own. |
| Parameter file ⚙️ | Defines database instance settings at startup. Can be a plain text pfile or a server parameter spfile. |
| Online redo log files 🔄 | Store all changes made to the database in real time, essential for recovery. Shared by the entire CDB. |
💡 Recommended Practice
Maintain multiple copies of control files and redo log files in different locations to avoid single points of failure (multiplexing).
📁 Other Important System Files (Outside the CDB)
| File Type | Description |
|---|---|
| Automatic Diagnostic Repository (ADR) 📂 | Centralized repository for diagnostic data like traces, dumps, alert logs, and health reports across Oracle products. |
| Backup files 💾 | Used to restore the database after failures or data loss. |
| Archived redo log files 🗃️ | Contain historical redo data for recovery purposes when combined with backups. |
| Password file 🔐 | Enables remote login for users with admin roles (SYSDBA, SYSOPER, etc.) for management tasks. |
| Keystores 🔑 | Secure storage for authentication and encryption keys. Supports software and hardware keystores (PKCS#11 compatible). |
| Block change tracking file ⚡ | Speeds up incremental backups by tracking changed blocks only. |
| Flashback logs ⏪ | Allow reverting the database to a previous state using flashback technology. Requires a configured fast recovery area. |
🛠️ DBA Tip of the Day
💡 Multiplex control files and redo logs to avoid downtime. Also, enable Flashback Database for easier recovery if your environment supports it.