Re: WAL Rate Limiting

On Thu, Feb 20, 2014 at 2:43 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> The design choice of making the limit only apply to bulk ops is
> because that is where the main problem lies. Rate limiting will cause
> a loss of performance in the main line for non-bulk operations, so
> adding tests there will not be valuable.

This isn't a bad point. If you do a massive UPDATE or INSERT you
probably do want the ability to limit the damage to your replication
lag but if you're an OLTP worker and you just happen to handle a
disproportionate amount of the incoming requests you wouldn't. But
then presumably you would just set that GUC that way where your OLTP
workers would run without any limits and your batch jobs would set a
limit.

As I said it wouldn't be terrible if the patch went in and could only
handle cluster/vacuum/create index. They're by far the most common
causes of problems and most people who do massive UPDATES or INSERTS
quickly discover they want to do it in batches of a few thousand rows
anyways so they can limit the speed themselves.

There's a decent argument to made for incremental changes too. If we
add a feature like this for these operations then we'll find out how
well it works in practice and whether users need finer control or what
other sources become the next problem before we've invested a whole
lot in a general solution.

--
greg