Is it true that binary backups always take less space than text backups?

Question

Options

• AA. No, because binary backups only contain data, and not statements required to insert data into the tables.
• BB. No, because text backups can have optimizations, which make them smaller, such as updating many rows at once.
• CC. No, because if InnoDB tables contain many empty pages, they could take more space than the INSERT statements.
• DD. Yes, because even if InnoDB tables contain many empty pages, text backups have empty INSERT statements for them.

• A
  25% (6)
• B
  4% (1)
• C
  58% (14)
• D
  13% (3)

Explanation

Option C is correct because binary backups (physical backups) copy the raw InnoDB data files page by page, including pages that are allocated but contain no actual row data - wasted space from deletions or fragmentation is preserved as-is. A text backup (like mysqldump), by contrast, generates only INSERT statements for rows that actually exist, so a table with massive empty-page overhead produces a compact SQL file far smaller than the bloated physical files.

Option A is wrong because it gets the direction of the logic backwards - saying binary backups omit SQL statements is a reason they could be smaller, not larger, and it ignores the empty-page problem entirely. Option B is wrong because text backup "optimizations" like extended inserts (multiple rows per INSERT) are a real feature, but they are a compression-of-syntax trick and do not reliably make text backups smaller than binary ones across all scenarios - this is not a valid counter-argument to the general claim. Option D is simply false: text backups contain no representation whatsoever of empty InnoDB pages, so there are no "empty INSERT statements" for them.

Memory tip: Think of a binary backup as a photocopier that copies every page in a book - blank pages included. A text backup is a scribe who only writes down sentences that have words. A half-empty book gets copied in full by the photocopier but produces a short manuscript for the scribe.

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