Re: Using quicksort for every external sort run

On Sat, Dec 12, 2015 at 12:10 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> I have a question about the terminology used in this patch. What is a
> tuple proper? What is it in contradistinction to? I would think that
> a tuple which is located in its own palloc'ed space is the "proper"
> one, leaving a tuple allocated in the bulk memory pool to be
> called...something else. I don't know what the
> non-judgmental-sounding antonym of postpositive "proper" is.

"Tuple proper" is a term that appears 5 times in tuplesort.c today. As
it says at the top of that file:

/*
* The objects we actually sort are SortTuple structs. These contain
* a pointer to the tuple proper (might be a MinimalTuple or IndexTuple),
* which is a separate palloc chunk --- we assume it is just one chunk and
* can be freed by a simple pfree(). SortTuples also contain the tuple's
* first key column in Datum/nullflag format, and an index integer.

> Also, if I am reading this correctly, when we refill a pool from a
> logical tape we still transform each tuple as it is read from the disk
> format to the memory format. This inflates the size quite a bit, at
> least for single-datum tuples. If we instead just read the disk
> format directly into the pool, and converted them into the in-memory
> format when each tuple came due for the merge heap, would that destroy
> the locality of reference you are seeking to gain?

Are you talking about alignment?

--
Peter Geoghegan