Can I Remove Data from Deleted InnoDB Tables Without a Full Database Rebuild?

Optimizing MySQL InnoDB Storage Engine for Data Removal

Problem: Is it possible to remove data from deleted tables in a MySQL InnoDB storage engine without rebuilding the entire database?

Answer: Yes, it is possible through a comprehensive cleanup process.

Explanation:

InnoDB stores various types of data in its ibdata1 file, including table data, indexes, and system metadata. When tables are deleted, their data and indexes remain within ibdata1, even though they are no longer accessible. This can lead to wasted space and performance degradation over time.

Cleanup Process:

1. Dump Database: Create a SQL dump of all databases except for mysql and information_schema.
2. Drop Databases: Drop all databases except for mysql and information_schema.
3. Disable Fast Shutdown: Set innodb_fast_shutdown to 0 to flush transactional changes from log files.
4. Shutdown MySQL: Stop the MySQL server.
5. Modify Configuration: Add innodb_file_per_table, innodb_flush_method=O_DIRECT, innodb_log_file_size, and innodb_buffer_pool_size settings to /etc/my.cnf.
6. Delete ibdata files:* Remove all ibdata and ib_logfile* files.
7. Restart MySQL: Start MySQL, which will recreate ibdata1 with only metadata.
8. Import Database Dump: Restore the previously exported SQL dump.

After this process, ibdata1 will contain only metadata, while individual tables will reside in their own .ibd files. This allows for optimization of individual tables using OPTIMIZE TABLE, reducing wasted space and improving performance.

Note: It is essential to ensure that user grants are properly re-established after dropping databases.

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