Re: [PATCH] pg_dump: lock tables in batches

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>

To: Andres Freund <andres@anarazel.de>

Cc: Aleksander Alekseev <aleksander@timescale.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2022-12-07T17:28:03Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

During pg_dump startup, acquire table locks in batches.
- 5f53b42cfd05 16.0 landed

Andres Freund <andres@anarazel.de> writes:
> On 2022-12-07 10:44:33 -0500, Tom Lane wrote:
>> I have a strong sense of deja vu here.  I'm pretty sure I experimented
>> with this idea last year and gave up on it.  I don't recall exactly
>> why, but either it didn't show any meaningful performance improvement
>> for me or there was some actual downside (that I'm not remembering
>> right now).

> IIRC the case we were looking at around 989596152 were CPU bound workloads,
> rather than latency bound workloads. It'd not be surprising to have cases
> where batching LOCKs helps latency, but not CPU bound.

Yeah, perhaps.  Anyway my main point is that I don't want to just assume
this is a win; I want to see some actual performance tests.

> I wonder if "manual" batching is the best answer. Alexander, have you
> considered using libpq level pipelining?

I'd be a bit nervous about how well that works with older servers.

			regards, tom lane