In MySQL MyISAM tables how do you free up disk space after deleting a lot of records in a table?

In MySQL with MyISAM tables, deleting rows does not automatically shrink the physical .MYD data file. To reclaim disk space after large deletions, you need to run:

OPTIMIZE TABLE your_table_name;

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🔧 What OPTIMIZE TABLE does for MyISAM:

• Rewrites the entire .MYD file (data file) and .MYI file (index file).
• Removes unused space left by deleted rows.
• Reorders and defragments indexes.
• Frees up disk space and improves performance.

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🛠️ Example:

OPTIMIZE TABLE suppression.mailserverdomains_segfilter;

After running this, check the file size:

ls -lh /var/lib/mysql/suppression/mailserverdomains_segfilter.*

You should see .MYD shrink if deletions were significant.

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⚠️ Notes:

• This operation locks the table during optimization.
• It can be slow on large tables — consider running during off-peak hours.
• Works only for MyISAM — for InnoDB, you’d use ALTER TABLE ... ENGINE=InnoDB or rely on innodb_file_per_table.

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