[necro]

Author states that he is using innodb and insert delayed is a myisam mechanism. Of course in innodb the buffer pool / insert buffers can be thought of the same way. The delay the author is noting is probably due to flush of the log file data.

If you configure innodb correctly it comes down how much IO you can do on your log fs, to make sure you can sustain some update rate to this sequential log. Then nest is the IO to the db fs, so you can sustain the rate of the flushes. You can tune some of this much better with some percona mysql patches. Innodb does insert batching for you to minimize IO, and if you are doing updates to the same data it may even buffer the changes in buffer pool.