Horton

Re: POC: converting Lists into arrays

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Peter Geoghegan <pg@bowt.ie>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-02-25T21:43:24Z
Lists: pgsql-hackers 
Hi,

On 2019-02-25 22:35:37 +0100, Tomas Vondra wrote:
> So let's say we want to measure the improvement this patch gives us.
> What would be some reasonable (and corner) cases to benchmark? I do have
> some ideas, but as you've been looking at this in the past, perhaps you
> have something better.

I think queries over tables with a fair number of columns very easily
stress test the list overhead around targetlists - I don't have a
profile lying around, but the overhead of targetlist processing
(ExecTypeFromTL etc) at execution time clearly shows up. Larger
individual expressions can easily show up via eval_const_expressions()
etc and ExecInitExpr().  Both probably can be separated into benchmarks
with prepared statements (ExecTypeFromTl() and ExecInitExpr() will show
up, but planner work obviously not), and non-prepared benchmarks will
stress the planner more.  I suspect there's also a few planner benefits
with large numbers of paths, but I don't quite remember the profiles
well enough to construct a benchmark from memory.

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.