On Wed, Mar 1, 2017 at 6:02 AM, Sven R. Kunze <srku...@mail.de> wrote:
> On 28.02.2017 17:49, Jeff Janes wrote: > > Oh. In my hands, it works very well. I get 70 seconds to do the {age: > 20} query from pure cold caches, versus 1.4 seconds from cold caches which > was followed by pg_prewarm('docs','prefetch'). > > How much RAM do you have? Maybe you don't have enough to hold the table > in RAM. What kind of IO system? And what OS? > > > On my test system: > > RAM: 4GB > IO: SSD (random_page_cost = 1.0) > OS: Ubuntu 16.04 > 4GB is not much RAM to be trying to pre-warm this amount of data into. Towards the end of the pg_prewarm, it is probably evicting data read in by the earlier part of it. What is shared_buffers? Cheers, Jeff