Re: Replacement Selection

<mac_man2005(at)hotmail(dot)it> writes:
> 3) Start run generation. As for this phase, I see PostgreSQL code (as Knuth
> algorithm) marks elements belonging to runs in otder to know which run they
> belong to and to know when the current heap has finished building the
> current run. I don't memorize this kind of info. I just output from heap to
> run all of the elements going into the current run. The elements supposed to
> go into the next run (I call them "dead records") are still stored into main
> memory, but as leaves of the heap. This implies reducing the heap size and
> so heapifying a smaller number of elements each time I get a dead record
> (it's not necessary to sort dead records). When the heap size is zero a new
> run is created heapifying all the dead records currently present into main
> memory.

Why would this be an improvement over Knuth? AFAICS you can't generate
longer runs this way, and it's not saving any time --- in fact it's
costing time, because re-heapifying adds a lot of new comparisons.

regards, tom lane