Re: Turning off HOT/Cleanup sometimes

On Tue, Apr 14, 2015 at 6:07 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 11 March 2015 at 20:55, Peter Eisentraut <peter_e@gmx.net> wrote:
>> I don't know how to move forward.  We could give users a knob: This
>> might make your queries faster or not -- good luck.  But of course
>> nobody will like that either.
>
> What is clear is that large SELECT queries are doing the work VACUUM
> should do. We should not be doing large background tasks (block
> cleanup) during long running foreground tasks. But there is no need
> for changing behaviour during small SELECTs. So the setting of 4 gives
> current behaviour for small SELECTs and new behaviour for larger
> SELECTs.

Peter commented previously that README.HOT should get an update.  The
relevant section seems to be "When can/should we prune or
defragment?".

I wonder if it would be a useful heuristic to still prune pages if
those pages are already dirty.

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