Horton

Re: POC: converting Lists into arrays

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <david.rowley@2ndquadrant.com>
Cc: Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-02T23:11:43Z
Lists: pgsql-hackers

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Here's a v3 incorporating Andres' idea of trying to avoid a separate
palloc for the list cell array.  In a 64-bit machine we can have up
to five ListCells in the initial allocation without actually increasing
space consumption at all compared to the old code.  So only when a List
grows larger than that do we need more than one palloc.

I'm still having considerable difficulty convincing myself that this
is enough of a win to justify the bug hazards we'll introduce, though.
On test cases like "pg_bench -S" it seems to be pretty much within the
noise level of being the same speed as HEAD.  I did see a nice improvement
in the test case described in
https://www.postgresql.org/message-id/6970.1545327857@sss.pgh.pa.us
but considering that that's still mostly a tight loop in
match_eclasses_to_foreign_key_col, it doesn't seem very interesting
as an overall figure of merit.

I wonder what test cases Andres has been looking at that convince
him that we need a reimplementation of Lists.

			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.