Horton

Re: POC: converting Lists into arrays

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, David Rowley <david.rowley@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-04T22:11:01Z
Lists: pgsql-hackers 
Hi,

On 2019-03-04 16:28:40 -0500, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > I don't buy this. I think e.g. redisgning the way we represent
> > targetlists would be good (it's e.g. insane that we recompute
> > descriptors out of them all the time), and would reduce their allocator
> > costs.
> 
> Maybe we're not on the same page here, but it seems to me that that'd be
> addressable with pretty localized changes (eg, adding more fields to
> TargetEntry, or keeping a pre-instantiated output tupdesc in each Plan
> node).  But if the concern is about the amount of palloc bandwidth going
> into List cells, we're not going to be able to improve that with localized
> data structure changes; it'll take something like the patch I've proposed.

What I'm saying is that it'd be reasonable to replace the use of list
for targetlists with 'list2' without a wholesale replacement of all the
list code, and it'd give us benefits.


> I find it interesting that you get different results.

What I reported weren't vanilla pgbench -S results, so there's that
difference. If measure the DO loop based test I posted, do you see a
difference?

Greetings,

Andres Freund

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.