Horton

Re: POC: converting Lists into arrays

Oleksandr Shulgin <oleksandr.shulgin@zalando.de>

View thread View on postgr.es
From: Oleksandr Shulgin <oleksandr.shulgin@zalando.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: jesper.pedersen@redhat.com, David Rowley <david.rowley@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-07-02T07:35:18Z
Lists: pgsql-hackers 
On Tue, Jul 2, 2019 at 1:27 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

>
> So I think this is a win, and attached is v7.
>

Not related to the diff v6..v7, but shouldn't we throw additionally a
memset() with '\0' before calling pfree():

+        ListCell   *newelements;
+
+        newelements = (ListCell *)
+            MemoryContextAlloc(GetMemoryChunkContext(list),
+                               new_max_len * sizeof(ListCell));
+        memcpy(newelements, list->elements,
+               list->length * sizeof(ListCell));
+        pfree(list->elements);
+        list->elements = newelements;

Or is this somehow ensured by debug pfree() implementation or does it work
differently together with Valgrind?

Otherwise it seems that the calling code can still be hanging onto a list
element from a freed chunk and (rather) happily accessing it, as opposed to
almost ensured crash if that is zeroed before returning from enlarge_list().

Cheers,
--
Alex

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.