Baked data is bigger than postcard data

[sffc]

trafficstars

I computed fingerprints.csv based on both baked_size and postcard_size.

Baked is equal in size or bigger than postcard for every data marker. A selection of the biggest offenders by overall size or percentage:

Marker Path	Postcard Size	Baked Size	Growth
list/or@2	3780B	31520B	734%
plurals/ranges@1	64B	524B	719%
percent/essentials@1	415B	2945B	610%
decimal/symbols@1	2040B	8905B	337%
relativetime/narrow/second@1	7678B	26032B	239%
units/displaynames@1	963404B	2062721B	114%
currency/extended@1	1908533B	3134831B	64.3%
displaynames/languages@1	1521724B	1557050B	2.32%

The good news is that many of these keys will be improved under #5230 or #5379.

Should we do anything?

@robertbastian @Manishearth

[robertbastian]

For list the explanation is that the data struct contains 10 cows (4 patterns of 1 cow, and two conditions of 3 cows each), but usually only encodes tiny texts (, , and, etc.). Unit and And data doesn't show up because the Spanish/Hebrew regexes equalise things between baked and postcard. So it's a similar problem to decimal formatter.

[Manishearth]

"baked size" here is the size of the .rs file, yes?

[robertbastian]

no, an estimate for in-memory size, ignoring &'static deduplication

[zbraniecki]

in-memory size means actual PSS cost? Can we also calculate on-disk binary size impact?

[robertbastian]

If you tell me what PSS is I might be able to answer this

[sffc]

list/and@1 also showed up, but I didn't take the time to copy it into the table; I tried to include a representative cross-section in the OP.

"baked size" refers to the in-memory size based on the bake_size, which is core::mem::size_of plus borrows_size.

These numbers are roughly reflective of what happens when I compile ICU4X with the compiled_data feature versus when I build Postcard data with icu4x-datagen. compiled_data produces a larger binary than no-default-features with postcard.

[sffc]

Note: I have some measurements in https://github.com/unicode-org/icu4x/issues/1317#issuecomment-2330283151 that illustrate the two types of binary size consumed by the baked data: the strings themselves (borrows_size) and the struct stacks (size_of).