Re: [PATCH] pg_dump: lock tables in batches

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2022-12-07 17:53:05 -0500, Tom Lane wrote:
>> Is "-s" mode actually a relevant criterion here? With per-table COPY
>> commands added into the mix you could not possibly get better than 2x
>> improvement, and likely a good deal less.

> Well, -s isn't something used all that rarely, so it'd not be insane to
> optimize it in isolation. But more importantly, I think the potential win
> without -s is far bigger than 2x, because the COPYs can be done in parallel,
> whereas the locking happens in the non-parallel stage.

True, and there's the reduce-the-lock-window issue that Jacob mentioned.

> With just a 5ms delay, very well within normal network latency range, I get:
> [ a nice win ]

OK. I'm struggling to figure out why I rejected this idea last year.
I know that I thought about it and I'm fairly certain I actually
tested it. Maybe I only tried it with near-zero-latency local
loopback; but I doubt that, because the potential for network
latency was certainly a factor in that whole discussion.

One idea is that I might've tried it before getting rid of all the
other per-object queries, at which point it wouldn't have stood out
quite so much. But I'm just guessing. I have a nagging feeling
there was something else.

Oh well, I guess we can always revert it if we discover a problem later.

regards, tom lane