Re: Memory-Bounded Hash Aggregation

On Tue, 2020-02-04 at 18:42 +0800, Adam Lee wrote:
> The minheap looks good, have you tested the performance and aggregate
> validation?

Not sure exactly what you mean, but I tested the min heap with both
Sort and HashAgg and it performs well.

> About the "Cap the size of the LogicalTapeSet's freelist" and "Don't
> bother tracking free space for HashAgg at all" you mentioned in last
> mail, I suppose these two options will lost the disk space saving
> benefit since some blocks are not reusable then?

No freelist at all will, of course, leak the blocks and not reuse the
space.

A capped freelist is not bad in practice; it seems to still work as
long as the cap is reasonable. But it feels too arbitrary, and could
cause unexpected leaks when our assumptions change. I think a minheap
just makes more sense unless the freelist just becomes way too large.

Regards,
    Jeff Davis