Re: Optimizing ResouceOwner to speed up COPY - Mailing list pgsql-hackers

On 18/10/2025 01:49, Tomas Vondra wrote:
> On 10/17/25 12:32, Tomas Vondra wrote:
>>
>>
>> On 10/17/25 10:31, Heikki Linnakangas wrote:
>>>>   typedef struct ResourceElem
>>>>   {
>>>>       Datum        item;
>>>> +    uint32        count;                /* number of occurrences */
>>>>       const ResourceOwnerDesc *kind;    /* NULL indicates a free hash
>>>> table slot */
>>>>   } ResourceElem;
>>>
>>> Hmm, the 'count' is not used when the entry is stored in the array.
>>> Perhaps we should have a separate struct for array and hash elements
>>> now. Keeping the array small helps it to fit in CPU caches.
>>
>> Agreed. I had the same idea yesterday, but I haven't done it yet.
>
> The attached v2 does that - it adds a separate ResourceHashElem for the
> has table, and it works. But I'm not sure I like it very much, because
> there are two places that relied on both the array and hash table using
> the same struct to "walk" it the same way.
>
> For ResourceOwnerSort() it's not too bad, but ResourceOwnerReleaseAll()
> now duplicates most of the code. It's not terrible, but also not pretty.
> I can't think of a better way, though.

Looks fine to me. The code duplication is not too bad IMO.

Here's a rebased version of the micro-benchmark I used when I was
working on the ResourceOwner refactoring
(https://www.postgresql.org/message-id/d746cead-a1ef-7efe-fb47-933311e876a3%40iki.fi).


I ran it again on my laptop. Different from the one I used back then, so
the results are not comparable with the results from that old thread.

Unpatched (commit 18d26140934):

postgres=# \i contrib/resownerbench/snaptest.sql
  numkeep | numsnaps | lifo_time_ns | fifo_time_ns
---------+----------+--------------+--------------
        0 |        1 |         11.6 |         11.1
        0 |        5 |         12.1 |         13.1
        0 |       10 |         12.3 |         13.5
        0 |       60 |         14.6 |         19.4
        0 |       70 |         16.0 |         18.1
        0 |      100 |         16.7 |         18.0
        0 |     1000 |         18.1 |         20.7
        0 |    10000 |         21.9 |         29.5
        9 |       10 |         11.0 |         11.1
        9 |      100 |         14.9 |         20.0
        9 |     1000 |         16.1 |         24.4
        9 |    10000 |         21.9 |         25.7
       65 |       70 |         11.7 |         12.5
       65 |      100 |         13.9 |         14.8
       65 |     1000 |         16.7 |         17.8
       65 |    10000 |         22.5 |         27.8
(16 rows)

v2-0001-Deduplicate-entries-in-ResourceOwner.patch:

postgres=# \i contrib/resownerbench/snaptest.sql
  numkeep | numsnaps | lifo_time_ns | fifo_time_ns
---------+----------+--------------+--------------
        0 |        1 |         10.8 |         10.6
        0 |        5 |         11.5 |         12.3
        0 |       10 |         12.1 |         13.0
        0 |       60 |         13.9 |         19.4
        0 |       70 |         15.9 |         18.7
        0 |      100 |         16.0 |         18.5
        0 |     1000 |         19.2 |         21.6
        0 |    10000 |         22.4 |         29.0
        9 |       10 |         11.2 |         11.3
        9 |      100 |         14.4 |         19.9
        9 |     1000 |         16.4 |         23.8
        9 |    10000 |         22.4 |         25.7
       65 |       70 |         11.4 |         12.1
       65 |      100 |         14.8 |         17.0
       65 |     1000 |         16.9 |         18.1
       65 |    10000 |         22.5 |         28.5
(16 rows)

v20251016-0001-Deduplicate-entries-in-ResourceOwner.patch:

postgres=# \i contrib/resownerbench/snaptest.sql
  numkeep | numsnaps | lifo_time_ns | fifo_time_ns
---------+----------+--------------+--------------
        0 |        1 |         11.3 |         11.1
        0 |        5 |         12.3 |         13.0
        0 |       10 |         13.0 |         14.1
        0 |       60 |         14.7 |         20.5
        0 |       70 |         16.3 |         19.0
        0 |      100 |         16.5 |         18.4
        0 |     1000 |         19.0 |         22.4
        0 |    10000 |         23.2 |         29.6
        9 |       10 |         11.2 |         11.1
        9 |      100 |         14.8 |         20.5
        9 |     1000 |         16.8 |         24.3
        9 |    10000 |         23.3 |         26.5
       65 |       70 |         12.4 |         13.0
       65 |      100 |         15.2 |         16.6
       65 |     1000 |         16.9 |         18.4
       65 |    10000 |         23.4 |         29.3
(16 rows)

These are just a single run on my laptop, the error bars on individual
numbers are significant. But it seems to me that V2 is maybe a little
faster when the entries fit in the array.

- Heikki