Defer Memory Allocation of AHI Hash Tables Until AHI Is Enabled

[SongLibing]

Problem

The AHI hash tables are initialized at startup even when AHI is disabled. They are initialized with
buf_pool_get_curr_size()/sizeof(void *)/64 cells. Each cell takes 8 bytes. So the total memory they occupy is approximately equal to 1/64 of the buffer pool size. The memory is wasted if AHI is disabled. On large servers, initializing large hash tables slows startup.

Solution

This commit initializes the AHI hash tables with one cell per AHI partition if AHI is disabled. The hash tables are restored to their normal size before AHI is enabled.

With one slot existing, the AHI system is fully initialized. This preserves the invariant that the per-partition hash table objects always exist.

During a buffer pool resizing, AHI is temporarily disabled. If AHI was enabled when the resize started, its full-sized hash tables are retained and resized only when necessary, avoiding an unnecessary shrink-and-restore cycle.

What does this change do?

https://bugs.mysql.com/bug.php?id=112223

Why is it needed?

This patch reduces memory usage and startup time when AHI is disabled. AHI has been disabled by default since 8.4 and AHI is not recommended for production use. Therefore, without this commit, most of the server would wastes an amount of memory approximately equal to 1/64 of buffer pool size.

How was it tested?

• Added/updated MTR tests under mysql-test/
• scripts/ci/mtr.sh passes locally
• Ran the relevant full suite (name it): ______

Contributor checklist

• Code is formatted (scripts/ci/format.sh)
• Commits are focused with descriptive messages

AI assistance

• I did not use AI assistance for this contribution
• I used AI assistance for this contribution

If AI assistance was used, describe the tool(s) and extent of use: Port the patch, added more testcases.

Areas touched

InnoDB