On Fri, Aug 12, 2011 at 12:23 PM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
I think it would also be fairly simple to decrease levelstep and/or adjust buffersize on-the-fly. The trick would be in figuring out the heuristics on when to do that.
I would be simple to decrease levelstep to the it's divider. It seems quite hard to dicrease it, for example, from 3 to 2. Also, it's pretty hard to detect that sub-tree actually doen't fit to the cache. I don't see much difficulties in buffersize runtime tuning.
Another thing occurred to me while looking at the buffer emptying process: At the moment, we stop emptying after we've flushed 1/2 buffer size worth of tuples. The point of that is to avoid overfilling a lower-level buffer, in the case that the tuples we emptied all landed on the same lower-level buffer. Wouldn't it be fairly simple to detect that case explicitly, and stop the emptying process only if one of the lower-level buffers really fills up? That should be more efficient, as you would have "swap" between different subtrees less often.
Yes, it seems reasonable to me.
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With best regards,
Alexander Korotkov.