Which statement best describes the purpose of the InnoDB buffer pool?

Question

Options

• AIt is amount of buffers available during a transaction.
• BIt caches only the indexes for InnoDB tables.
• CIt caches data and indexes for InnoDB tables.
• DIt holds changes made during a transaction before they are written to the log.
• EIt is a pool of memory for SQL query sort operations from within the InnoDB engine.

• B
  3% (1)
• C
  91% (32)
• D
  6% (2)

Explanation

C is correct because the InnoDB buffer pool is MySQL's primary in-memory cache, storing both data pages and index pages from InnoDB tables to reduce expensive disk I/O - it's the single most impactful memory configuration for InnoDB performance.

Why the distractors are wrong:

• A confuses the buffer pool with transaction-related memory; it is persistent across transactions, not scoped to one.
• B is a half-truth - the buffer pool does cache indexes, but it also caches data pages, so "only indexes" is incorrect.
• D describes the InnoDB log buffer (redo log buffer), which temporarily holds uncommitted transaction changes before flushing to the redo log files.
• E describes the sort buffer (a per-session memory area), which is unrelated to InnoDB's buffer pool.

Memory tip: Think of the buffer pool as InnoDB's RAM disk - it mirrors the full table/index contents (data + indexes) in memory. The key phrase is "data AND indexes," which distinguishes it from all the other buffer types that handle only one thing.

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