Re: BUG #14378: when drop schema, standby will do many more than primary, and very slow, it's a bug?

On 2016-10-18 07:57:33 +0000, digoal@126.com wrote:
> The following bug has been logged on the website:
>
> Bug reference:      14378
> Logged by:          Zhou Digoal
> Email address:      digoal@126.com
> PostgreSQL version: 9.6.0
> Operating system:   CentOS 6.x x64
> Description:
>
>
>
> when i use postgresql 9.6.0 for primary-standby, i drop a schema on primary,
> but it's apply very slow on standby.
>
> the wal send very fast, but apply very slow, i think the syscall more than
> it on primary?
>
> this is my test:

There's some O(n^2) behaviour around lock release and acquire during
replay IIRC.  See for example the thread around
http://archives.postgresql.org/message-id/20140630231741.GA30918%40alap3.anarazel.de

It's not entirely trivial to fix that though. E.g. the patch of Simon's
later in that thread wouldn't help in your situation.

Greetings,

Andres Freund