Which two options describe how MySQL Server allocates memory?

Question

Options

• AA. Each connection may have its own per-thread memory allocations.
• BB. Thread memory is pre-allocated up to thread_cache_size for performance.
• CC. Each thread allocates memory from a global pool.
• DD. Global memory resources are allocated at server startup.

• A
  94% (34)
• B
  3% (1)
• C
  3% (1)

Explanation

MySQL's memory model has two distinct layers: global memory allocated once at startup (e.g., InnoDB buffer pool, key buffer), and per-thread memory allocated dynamically for each client connection (e.g., sort buffers, join buffers). Option A is correct because each thread - one per connection - gets its own independent memory allocations governed by variables like sort_buffer_size. Option D is correct because shared global structures are reserved when the server starts, not on demand.

Why B is wrong: thread_cache_size controls how many threads MySQL holds idle for reuse after a connection closes - it is about thread recycling, not memory pre-allocation. No memory is "pre-reserved" up to that count.

Why C is wrong: Per-thread memory is allocated from the OS allocator independently for each thread. MySQL does not maintain a single managed global pool from which threads carve out their working memory - global and per-thread allocations are entirely separate categories.

Memory tip: Think of two buckets - one filled once at startup (global: buffer pool, caches) and one filled fresh per connection (per-thread: sort, join, read buffers). Startup = global; connection = per-thread. That maps directly to D and A.

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