What is SQLite's in-memory database? How to use it?

SQLite's in-memory database provides a fast data storage solution:

1. Creating In-Memory Database

   • Use special database name :memory:
   • Data is stored only in memory, not written to disk

   sql
   -- Create in-memory database connection
   sqlite3 :memory:

2. Characteristics of In-Memory Database

   • Extremely fast read/write speed: No disk I/O overhead
   • Temporary: Data is lost after database closes
   • Suitable for caching: Used for temporary storage and calculation results
   • Transaction support: Supports complete transaction functionality

3. Use Cases

   • Temporary data processing and transformation
   • Intermediate result storage for complex queries
   • Unit testing and integration testing
   • Caching frequently accessed data
   • Temporary storage for data import/export

4. Combining In-Memory and Disk Databases

   • Can attach tables from disk database to in-memory database

   sql
   ATTACH DATABASE 'disk.db' AS disk_db;

   • Perform complex operations in in-memory database, then write results back to disk

5. Shared Cache Mode

   • Multiple connections can share the same in-memory database
   • Use cache=shared connection parameter

   sql
   sqlite3 "file::memory:?cache=shared"

6. Performance Considerations

   • In-memory database performance far exceeds disk database
   • Suitable for read-intensive operations
   • May be limited by memory bandwidth during heavy writes
   • Need to monitor memory usage to avoid memory overflow

7. Limitations and Considerations

   • Data is not persistent, lost after closing
   • Limited by available memory size
   • Not suitable for long-term storage of important data
   • Need to regularly persist data to disk

In-memory database is a powerful feature of SQLite, especially suitable for scenarios requiring high-performance temporary data storage.