On Mon, Nov 24, 2014 at 3:26 PM, Thom Brown <thom@linux.com> wrote: > I haven't seen this mentioned anywhere (although it may have as I haven't > read through the entire history of it), but would others find it useful to > have ALTER SYSTEM support comments?
Oh, please no.
The main thing that caused us to have no way of modifying postgresql.conf via SQL for so many years is that it's not clear how you can sensibly rewrite a file with comments in it. For example, the default postgresql.conf file has stuff like this in it:
#variable = someval
If variable gets set to a non-default value, you might want to uncomment that line, but now you have to parse the comments, which will be tedious and error-prone and sometimes make stupid decisions:
#Back in days of yore when dinosaurs ruled the earth, we had #autovacuum_naptime=1h, but that turned out to be a bad idea. # #autovacuum_naptime=1min
I'm not sure this is an argument against supporting comments to postgresql.auto.conf since it's specifically intended not to be edited by humans, and commenting out a parameter will remove it from the file upon further ALTER SYSTEM invocations anyway.
It would perhaps be OK to have comments in postgresql.conf.auto if they were designated in some way that told us which specific comment was associated with which specific setting. But we need to be very careful not to design something that requires us to write a parser that can ferret out human intent from context clues.
Perhaps the parser could automatically remove any comment blocks which are followed by a blank/empty line.
So if we had:
---------------------
work_mem = '4MB'
# Set this lower as we're using a really fast disk interace
#seq_page_cost = '0.5'
# Set random_page_cost lower as we're using an SSD
random_page_cost = '1.0'
# This line has been manually added by a human without a newline
maintenance_work_mem = '1GB'
# This is an orphaned comment
---------------------
I would expect the next modification to the file to cause reduce it to:
---------------------
work_mem = '4MB'
# Set random_page_cost lower as we're using an SSD
