Re: Can I get some PostgreSQL developer feedback on these five general issues I have with PostgreSQL and its ecosystem?

On Mon, Sep 14, 2020 at 05:39:57PM -0400, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> tutiluren(at)tutanota(dot)com writes:
> > 1. All non-ANSI characters are turned into "?"s for application_name.
>
> Yeah, that's hard to do much with unfortunately. We cannot assume that
> all databases in an installation share the same encoding, so for globally
> visible strings like application_name, the only safe solution is to
> restrict them to ASCII.
>
> On the other hand, the very same thing could be said of database names
> and role names, yet we have never worried much about whether those were
> encoding-safe when viewed from databases with different encodings, nor
> have there been many complaints about the theoretical unsafety. So maybe
> this is just overly anal-retentive and we should drop the restriction,
> or at least pass through data that doesn't appear to be invalidly
> encoded.

Perhaps recode database/role names from the source
database's encoding into utf8, and then recode from utf8
to the destination database's encoding?

For "globally visible strings", maybe recode to the
client_encoding setting, or a new encoding setting for
this purpose since client_encoding seems to be linked
to the database that the client is connected to. I'd've
thought that the application name would arrive encoded
as client_encoding (which defaults to the database
encoding). Maybe globally visible strings need to be
recoded on arrival from the client_encoding to utf8 (or
a "server_encoding" or "global_encoding" setting) so
they are always stored in a known encoding so they can
be recoded as necessary when viewed via connections to
other databases using a different encoding.

Just some thoughts. If they don't make any sense, feel
free to ignore them. :-)

> > 5. Ever since my early days with PG in the mid-2000s, I've tried
> > numerous times to read the manual, wikis and comments for the
> > configuration files, specifically the performance directives, and asked
> > many, many times for help about that, yet never been able to figure out
> > what they want me to enter for all the numerous options. At this point,
> > it isn't me being lazy/stupid; it's objectively very difficult to
> > understand all of that.
>
> We do the best we can as far as the documentation goes; if you have
> concrete suggestions about how to improve that, we'll surely listen.

I thought the documentation on postgres performance tuning was fine.
Here's what I got from it (for a dedicated database server host):

shared_buffers = 1GB # Should be 1/4 of RAM
work_mem = 16MB # Should be bigger to do more sorts in-memory but it's per sort per user so not too big
maintenance_work_mem = 128MB # Should be <= 256MB to make vacuum fast without taking away too much RAM from other tasks
min_wal_size = 480MB # Should be at least 3 * 10 * 16MB to avoid too many checkpoints slowing down writes
checkpoint_completion_target = 0.9 # Should be 0.9 if checkpoint_segments was increased to spread out checkpoint writes
random_page_cost = 4.0 # Should be 4.0 for HDD, 1.5-2.5 for SSD, 1.0-1.01 if db fits entirely in RAM
effective_cache_size = 3GB # Should be 1/2 to 3/4 of RAM

It's the "Should..." comments that matter. And it might be out of date...
Actually, it is out of date. The comment for checkpoint_completion_target
refers to checkpoint_segments which no longer exists (since 9.5) so
disregard that.

cheers,
raf