What do the InnoDB insert buffer statistics mean?

Ever seen this in SHOW INNODB STATUS and wondered what it means?

Ibuf: size 1, free list len 4634, seg size 4636,

I’ve never been quite sure, and Peter didn’t really clarify things himself, so I took a look at the source. If I’m not mistaken, the seg size is really one more than the number of records the insert buffer can hold, the free list length is the number that aren’t in use, and the size is just seg_size - (1 + free_list_len). These seem to be kept in lockstep as records are inserted and merged.

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I'm Baron Schwartz, the founder and CEO of VividCortex. I am the author of High Performance MySQL and lots of open-source software for performance analysis, monitoring, and system administration. I contribute to various database communities such as Oracle, PostgreSQL, Redis and MongoDB. More about me.