Horton

Re: POC: converting Lists into arrays

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-02-25T18:30:56Z
Lists: pgsql-hackers 
On Mon, Feb 25, 2019 at 1:17 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I'm not following your point here.  If we change key data structures
> (i.e. parsetrees, plan trees, execution trees) to use some other list-ish
> API, that *in itself* breaks everything that accesses those data
> structures.  The approach I propose here isn't zero-breakage, but it
> requires far fewer places to be touched than a complete API replacement
> would do.

Sure, but if you have third-party code that touches those things,
it'll fail to compile.  With your proposed approach, there seems to be
a risk that it will compile but not work.

> Yup.  So are you saying that we'll never redesign parsetrees again?
> We break things regularly, as long as the cost/benefit justifies it.

I'm mostly objecting to the degree that the breakage is *silent*.

> I completely disagree.  Your proposal is probably an order of magnitude
> more painful than the approach I suggest here, while not really offering
> any additional performance benefit (or if you think there would be some,
> you haven't explained how).  Strictly on cost/benefit grounds, it isn't
> ever going to happen that way.

Why would it be ten times more painful, exactly?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.