Show metadata size

[hyanwong]

Fixes #2637 - I remembered this issue when writing some recent tutorial material.

I went for the absolute size rather than percentage, and simply appended the codec type, rather than having a separate column, as it seems simpler:

I will add tests if this seems like the right format:

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##             main    #3343   +/-   ##
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  Coverage   89.76%   89.76%           
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  Branches     5737     5738    +1     
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[hyanwong]

I just updated to a different style, with percentages. I thought it best not to show anything if the metadata and schema are both empty. Dunno if I prefer percentages or bytes? If percentages, perhaps the title should be e.g. "Metadata (%)"?

[jeromekelleher]

Bytes are better. How does this interact with the old "has metadata" flag? What happens when there is metadata but there's no schema (I think I see what it is not from rereading the code, but it would really help to use some variables and not try to make everything maximally cryptic).

Some simple unit tests here based on the output of metadata_details covering the various possibilities would be sufficient.

[hyanwong]

I'll go with bytes then. This replaces the "has_metadata" column (which I think is the right way to go: if there is text in there, it means either a schema is set or there is metadata). I'm trying not to bloat the tables with lots of extra text / columns, so if we are going with bytes, how about

No metadata, no schema =
Some metadata, no schema = (XXX bytes)
No metadata, schema set = schema_codec
Some metadata, schema set = schema_codec (XXX bytes)

So e.g.

╔═══════════╤════╤═════════╤═════════════════╗
║Table      │Rows│Size     │ Metadata (size) ║
╠═══════════╪════╪═════════╪═════════════════╣
║Edges      │   6│200 Bytes│                 ║
╟───────────┼────┼─────────┼─────────────────╢
║Individuals│   2│ 80 Bytes│  json (90 Bytes)║
╟───────────┼────┼─────────┼─────────────────╢
║Migrations │   0│  8 Bytes│                 ║
╟───────────┼────┼─────────┼─────────────────╢
║Mutations  │   0│ 16 Bytes│          struct ║
╟───────────┼────┼─────────┼─────────────────╢
║Nodes      │   7│204 Bytes│       (50 Bytes)║
╟───────────┼────┼─────────┼─────────────────╢
║Populations│   1│224 Bytes│struct (50 Bytes)║
╟───────────┼────┼─────────┼─────────────────╢
║Provenances│   1│  1.1 KiB│                 ║
╟───────────┼────┼─────────┼─────────────────╢
║Sites      │   0│ 16 Bytes│                 ║
╚═══════════╧════╧═════════╧═════════════════╝

? Other suggestions welcome, obviously. I could put e.g. an empty marker (e.g. -) in the blank columns, but I think that's just more confusing than leaving it blank?

The alternative is to have 2 columns, labelled e.g. Metadata schema and Metadata size? In this case would we put "" in the first column for the empty schema, and e.g. "0" in the second for no metadata?

[jeromekelleher]

I think it's confusing to omit the bytes value when it's empty, just say "0 Bytes". I think it's probably easier to understand if we have two columns all right.