Gregory Stark <stark@enterprisedb.com> writes:
> "Heikki Linnakangas" <heikki@enterprisedb.com> writes:
>> Markus Schiltknecht wrote:
>>> And why do you need lots of heap memory to do that? Anything wrong with the
>>> zipper approach I've outlined upthread?
>>
>> We're talking about a binary heap, with just one node per partition. AFAICT
>> it's roughly the same data structure as the zipper tree you envisioned, but not
>> implemented with separate executor nodes for each level.
> Not quite the same since the Executor-based implementation would have a static
> tree structure based on the partitions. Even if the partitions are all empty
> except for one or two you would still have to push the result records through
> all the nodes for the empty partitions.
Also, the overhead per executor node visit is not exactly trivial.
I think that "zipper" scheme would be quite slow compared to a standard
heap merge within a single node.
regards, tom lane
