Re: WAL Rate Limiting

On Wed, Jan 15, 2014 at 7:54 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> On Wed, Jan 15, 2014 at 3:20 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> We've discussed previously the negative impact of large bulk
>> operations, especially wrt WAL writes. Patch here allows maintenance
>> operations to have their WAL generation slowed down as a replication
>> lag prevention feature.
>>
>> I believe there was originally intended to be some work on I/O rate
>> limiting, but that hasn't happened and is in some ways orthogonal to
>> this patch and we will likely eventually want both.
>>
>> Single new parameter works very similarly to vacuum_cost_delay
>>
>> wal_rate_limit_delay = Xms
>
>
> Seems like a really bad name if we are only slowing down some commands -
> that seems to indicate we're slowing down all of them. I think it should be
> something that indicates that it only affects the maintenance commands.

And why should it only affect the maintenance commands anyway, and who
decides what's a maintenance command?

I thought Heroku suggested something like this previously, and their
use case was something along the lines of "we need to slow the system
down enough to do a backup so we can delete some stuff before the disk
fills". For that, it seems likely to me that you would just want to
slow everything down.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company