| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager |
| Date: | 2018-04-26 19:25:22 |
| Message-ID: | CA+TgmoYSKdPejVr7PYcEgGqzG++guMZpS6ieGTBf68DwnYgL4w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Apr 26, 2018 at 3:10 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> I think the real question is whether the scenario is common enough to
>> worry about. In practice, you'd have to be extremely unlucky to be
>> doing many bulk loads at the same time that all happened to hash to
>> the same bucket.
>
> With a bunch of parallel bulkloads into partitioned tables that really
> doesn't seem that unlikely?
It increases the likelihood of collisions, but probably decreases the
number of cases where the contention gets really bad.
For example, suppose each table has 100 partitions and you are
bulk-loading 10 of them at a time. It's virtually certain that you
will have some collisions, but the amount of contention within each
bucket will remain fairly low because each backend spends only 1% of
its time in the bucket corresponding to any given partition.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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