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: David Rowley <david.rowley@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-04T19:03:27Z
Lists: pgsql-hackers 
Hi,

On 2019-03-03 13:29:04 -0500, Tom Lane wrote:
> The cases I've been looking at suggest to me that we'd make far
> more progress on the excessive-palloc'ing front if we could redesign
> things to reduce unnecessary copying of parsetrees.  Right now the
> planner does an awful lot of copying because of fear of unwanted
> modifications of multiply-linked subtrees.  I suspect that we could
> reduce that overhead with some consistently enforced rules about
> not scribbling on input data structures; but it'd take a lot of work
> to get there, and I'm afraid it'd be easily broken :-(

Given the difficulty of this tasks, isn't your patch actually a *good*
attack on the problem? It makes copying lists considerably cheaper. As
you say, a more principled answer to this problem is hard, so attacking
it from the "make the constant factors smaller" side doesn't seem crazy?

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.