Misleading help text for storage.tsdb.retention.size

[acdha]

I installed 2.7.0 on a test server and ran into one point of confusion:

prometheus, version 2.7.0 (branch: HEAD, revision: 410ee9e04acb8f59f400858752ca82b4ef88035e)
  build user:       root@3bc81b516055
  build date:       20190128-10:09:51
  go version:       go1.11.5

The help text for --storage.tsdb.retention.size says this:

[EXPERIMENTAL] Maximum number of bytes that can be stored for blocks. Units supported: KB, MB, GB, TB, PB. This flag is experimental and can be changed in future releases.

I interpreted that to mean that it followed the common convention of accepting a number as bytes while allowing units as a shortcut for readability. What it actually means is that you must specify one of the units or get an error like this:

Error parsing commandline arguments: units: unknown unit  in 96589578240b

It would be nice if it either defaulted to bytes or the wording was something like “Limit the maximum size of block storage. Specify the unit suffix using one of: KB, MB, GB, TB, PB.” to make it obvious that it's not optional.

[hphde]

Mh. Worked for me though because it explicitly lists supported units and obviously bytes are not listed.

[acdha]

@hphde bytes are specified as the base unit in the previous sentence and most tools assume you're providing that value directly unless otherwise specified. For example, dd has this:

BLOCKS and BYTES may be followed by the following multiplicative suffixes: c =1, w =2, b =512, kB =1000, K =1024, MB =10001000, M =10241024, xM =M GB =100010001000, G =102410241024, and so on for T, P, E, Z, Y.

Perhaps that's really an argument saying that “unit” is the wrong term — the GNU utilities generally use “multiplicative suffix”:

Put size bytes of input into each output file. size may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: …

https://www.gnu.org/software/coreutils/manual/html_node/split-invocation.html

A block size specification can be a positive integer specifying the number of bytes per block, or it can be human-readable or si to select a human-readable format. Integers may be followed by suffixes that are upward compatible with the SI prefixes for decimal multiples and with the ISO/IEC 80000-13 (formerly IEC 60027-2) prefixes for binary multiples.

https://www.gnu.org/software/coreutils/manual/html_node/Block-size.html#Block-size

[beorn7]

Ran into the same issue. Definitely 👍 for having bytes as default if no unit specified.