Horton

Re: POC: converting Lists into arrays

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Daniel Gustafsson <daniel@yesql.se>
Cc: David Rowley <david.rowley@2ndquadrant.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-07-17T14:53:53Z
Lists: pgsql-hackers 
Daniel Gustafsson <daniel@yesql.se> writes:
> For cases where an Oid list is copied and then head elements immediately
> removed, as in fetch_search_path, couldn’t we instead use a counter and
> list_copy_tail to avoid repeated list_delete_first calls?

Perhaps, but I'm having a hard time getting excited about it.
I don't think there's any evidence that fetch_search_path is a
performance issue.  Also, this coding requires that the *only*
changes be deletion of head elements, whereas as it stands,
once we've copied the list we can do what we like.

> Since we’ve allowed list_delete_first on NIL for a long time, it seems
> reasonable to do the same for list_delete_last even though it’s hard to come up
> with a good usecase for deleting the last element without inspecting the list
> (a stack growing from the bottom perhaps?

Yeah, I intentionally made the edge cases the same.  There's room to argue
that both functions should error out on NIL, instead.  I've not looked
into that though, and would consider it material for a separate patch.

> Looking mainly at 0001 for now, I agree that the order is insignificant.

Thanks for looking!

			regards, tom lane

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.