Horton

Re: POC: converting Lists into arrays

David Rowley <david.rowley@2ndquadrant.com>

View thread View on postgr.es
From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jesper Pedersen <jesper.pedersen@redhat.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-07-16T02:56:46Z
Lists: pgsql-hackers 
On Tue, 16 Jul 2019 at 07:49, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> A possibly controversial point is that I made list_qsort() sort the
> given list in-place, rather than building a new list as it has
> historically.  For every single one of the existing and new callers,
> copying the input list is wasteful, because they were just leaking
> the input list anyway.  But perhaps somebody feels that we should
> preserve the "const input" property?  I thought that changing the
> function to return void, as done here, might be a good idea to
> ensure that callers notice its API changed --- otherwise they'd
> only get a warning about incompatible signature of the passed
> function pointer, which they might not notice; in fact I'm not
> totally sure all compilers would even give such a warning.
>
> If there's not complaints about that, I'm just going to go ahead
> and push this --- it seems simple enough to not need much review.

The only thoughts I have so far here are that it's a shame that the
function got called list_qsort() and not just list_sort().  I don't
see why callers need to know anything about the sort algorithm that's
being used.

If we're going to break compatibility for this, should we rename the
function too?

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Remove EState.es_range_table_array.

  2. Rationalize use of list_concat + list_copy combinations.

  3. Cosmetic improvements in setup of planner's per-RTE arrays.

  4. Make better use of the new List implementation in a couple of places

  5. Fix sepgsql test results for commit d97b714a2.

  6. Avoid using lcons and list_delete_first where it's easy to do so.

  7. Remove lappend_cell...() family of List functions.

  8. Clean up some ad-hoc code for sorting and de-duplicating Lists.

  9. Redesign the API for list sorting (list_qsort becomes list_sort).

  10. Remove dead code.

  11. Represent Lists as expansible arrays, not chains of cons-cells.

  12. Standardize some more loops that chase down parallel lists.

  13. Reimplement the linked list data structure used throughout the backend.