Horton

Re: POC: converting Lists into arrays

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-02-25T22:07:40Z
Lists: pgsql-hackers 
On Mon, Feb 25, 2019 at 1:51 PM Andres Freund <andres@anarazel.de> wrote:
> Those could trivially support distinguisiong at least between lists
> containing pointer, int, oid, or node. But even optionally doing more
> than that would be fairly easy. It's not those modules don't currently
> know the types of elements they're dealing with?
>
>
> > If you add a support for a new datatype, where does that leave
> > stored rules?
>
> We don't maintain stored rules across major versions (they break due to
> a lot of changes), so I don't quite understand that problem.

The point is that the implicit need to have support for serializing
and deserializing everything is something that constrains the design,
and must also constrain the design of any successor data structure.
The contents of pg_list.[ch] are not why it's a PITA to add support
for a new datatype. Also, most of the time the Lists are lists of
nodes, which is essentially an abstract base type for heterogeneous
types anyway. I don't really get what you mean about type safety,
because you haven't spelled it out in a way that acknowledges all of
this.

-- 
Peter Geoghegan

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.