Answered my own question. Cranking work_mem up to 350MB revealed that
the in-memory sort requires more memory than the disk sort.
On Wed, Aug 18, 2010 at 10:23 PM, Samuel Gendler
<sgendler@ideasculptor.com> wrote:
> I've got this explain: http://explain.depesz.com/s/Xh9
>
> And these settings:
> default_statistics_target = 50 # pgtune wizard 2010-08-17
> maintenance_work_mem = 1GB # pgtune wizard 2010-08-17
> constraint_exclusion = on # pgtune wizard 2010-08-17
> checkpoint_completion_target = 0.9 # pgtune wizard 2010-08-17
> effective_cache_size = 36GB # sam
> work_mem = 288MB # pgtune wizard 2010-08-17
> wal_buffers = 8MB # pgtune wizard 2010-08-17
> #checkpoint_segments = 16 # pgtune wizard 2010-08-17
> checkpoint_segments = 30 # sam
> shared_buffers = 11GB # pgtune wizard 2010-08-17
> max_connections = 80 # pgtune wizard 2010-08-17
> cpu_tuple_cost = 0.0030 # sam
> cpu_index_tuple_cost = 0.0010 # sam
> cpu_operator_cost = 0.0005 # sam
> #random_page_cost = 2.0 # sam
>
> I'm not understanding why it is sorting on disk if it would fit within
> a work_mem segment - by a fairly wide margin. Is there something else
> I can do to get that sort to happen in memory?
>
