| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | "Saul, Jean Paolo" <paolo(dot)saul(at)verizonconnect(dot)com> |
| Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, PostgreSQL mailing lists <pgsql-bugs(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: BUG #15609: synchronous_commit=off insert performance regression with secondary indexes |
| Date: | 2019-02-01 00:08:32 |
| Message-ID: | CAH2-Wzk8ihamcwG3Pd46XVyvTfGEGKBfQR6AJtT3ffdEnJgOGA@mail.gmail.com |
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| Lists: | pgsql-bugs |
On Wed, Jan 30, 2019 at 6:06 PM Saul, Jean Paolo
<paolo(dot)saul(at)verizonconnect(dot)com> wrote:
> I am testing your comment about low cardinality indexes, and changed my inserted values.
>
> for integers: (RANDOM()*10)::INT % 2
> for text: MD5(((RANDOM()*10)::INT % 2)::TEXT)
>
> The latest results show that text and integer indexes now behave poorly like the boolean index.
> The performance hit is visibly disappointing compared to versions prior to PG10.
FWIW, I cannot recreate this. I still have no reason to believe that
this problem with low cardinality indexes would be any worse on more
recent versions.
BTW, I think that you'll find that hash indexes don't do as well as
B-Tree indexes with lots of duplicates when reading.
--
Peter Geoghegan
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