Update "Tuning your configuration" section

[mwtoews]

Reading through the "Tuning your configuration" manual section, it seems it has aged behind multiple PostgreSQL releases, so this task is to update it. Here is what I've noticed (compared to PostgreSQL 9.5):

checkpoint_segments

was removed in PostgreSQL 9.5 (I'm not sure why), so note this change and consider removing it in December 2019 when PostgreSQL 9.4 is no longer supported.

constraint_exclusion

the default is partition. Remove mention of PostgreSQL 8.4, which was supported up to July 2014. Perhaps keep description for this setting in case someone is considering changing it.

shared_buffers

has had several defaults. For PostgreSQL versions 8.2 to 9.2 it was 32MB, and 9.3+ it is 128MB.

work_mem

the default was 1MB and was changed in 9.4 to 4MB. Furthermore, the example should show the units, e.g. SET work_mem TO '1200MB';

maintenance_work_mem

the default was 16MB and was changed in 9.4 to 64MB. Also, the example has a typo (i.e. ERROR: unrecognized configuration parameter "maintainence_work_mem"). A better example is SET maintenance_work_mem TO '1200MB';.

There have been many new configuration parameters added to PostgreSQL, are there any new tuning parameters that should be described?

[robe]

I know. It's one of those areas I really wanted to revisit but haven't had the time. If you want to provide a patch, (and save me some trouble), that would be very welcome.

I plan to revisit it before 2.3 release time at the very least.

[robe]

In 15139:

Bring Tuning section up to date, by incorporating some of Mike Toews changes
Add mention of configs to enable parallel queries
Get rid of broken link to Kevin Neufeld's old press and replace with PostgreSQL wiki
Closes #3452