Re: TIL: In pg_dump, beware the combo of "-Fd" and "-Z"

On 1/19/21 1:55 PM, David G. Johnston wrote:
> On Tuesday, January 19, 2021, Ron <ronljohnsonjr(at)gmail(dot)com
> <mailto:ronljohnsonjr(at)gmail(dot)com>> wrote:
>
>
> For a project using 9.6, I have this command backing up a database:
> So, for the 12 project, I copied it over, removing the "0", since I
> want these backups compressed.
>
>
> The versions in use doesn’t seem pertinent to the observation - this
> behavior hasn’t changed (at least in the docs).
>
>
> Since the -Z default is "6"
>
>
> It is?  Where do you see this?

https://www.postgresql.org/docs/12/app-pgdump.html

"-Z 0..9"
"the default is to compress at a moderate level."

It doesn't say "6", but every other bit of software I've used defaults to
level 6.

What's also interesting is that this section doesn't mention what it does
with directory format backups, though it does mention custom format.

"For the custom archive format, this specifies compression of individual
table-data segments, and the default is to compress at a moderate level."

Since -Fc and -Fd are so similar, I worked off the notion that -Z works
similarly for both.

>
>  I assumed that would compress the backup.  It didn't, acting instead
> like "-Z0".  Removing "-Z" made it compress.
>
> This surprised me, and is very counter-intuitive.  A bug?
>
>
> That we accept a -Z parameter without a number without complaint would be
> a bug given the documentation doesn’t indicate the number as being
> optional.  That “-Z” and “-Z 0” are equivalent makes sense if one allows “-Z”.

As mentioned above, -Z6 is the default on all the other software I use, so
worked of the notion that Postgres uses that default, too.

--
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