ef4e975a47
Answers the backlog's open "first step: diff the two readers across the disc and count disagreements", statically over every IDXD object. Of 7750 objects and 738922 named fields whose true value is numeric, legacy get_f32 is correct 39.42%, returns None (harmless) 43.04%, and returns a WRONG NUMBER 17.54% (129612 fields). The wrongness has an exact predicate: single-record objects 0 of 29822 wrong (0.00%); multi-record objects 129612 of 709100 (18.28%). The mechanism is in get_raw itself -- it flattens the pool to a token list, finds the FIRST occurrence of the key, and returns the preceding token, with no notion of records. So every record after the first inherits record 0's value: Weight truth=1.0 legacy=0.3, Points truth=10000 legacy=4000. Practical rule recorded: a get_f32 number from a single-record object is safe; from a multi-record object only the first record is. Withdrawn in the same document: my first sweep compared against "the string before THIS field's own key" and reported 65.90% -- that is not what get_raw does, so the figure is not the legacy reader's error rate.
2.8 KiB
✅ How wrong the legacy IDXD reader is — measured disc-wide
BACKLOG.md left this open: "the legacy value-before-key
string-pool reader is an approximation … every number in this corpus that came
out of get_f32/get_raw is re-checkable against ground truth but not yet
re-checked. First step: diff the two readers across the disc and count
disagreements." Done, statically, over every IDXD object on the disc.
The answer
7 750 IDXD objects, 738 922 named fields whose true value is numeric:
legacy get_f32 outcome |
fields | share |
|---|---|---|
| correct | 291 307 | 39.42 % |
returns None — no number produced, so harmless |
318 003 | 43.04 % |
| returns a WRONG NUMBER | 129 612 | 17.54 % |
✅ And the wrongness has an exact predicate
| object shape | numeric fields | wrong numbers |
|---|---|---|
| single-record | 29 822 | 0 — 0.00 % |
| multi-record | 709 100 | 129 612 — 18.28 % |
The legacy reader is exactly correct on single-record objects and unsafe on multi-record ones. Not approximately — zero disagreements in 29 822 fields.
The mechanism is in get_raw's own implementation: it flattens the string pool
to a token list, finds the first occurrence of the key, and returns the token
before it. It has no notion of records. So in an object with N records that each
carry a Weight, every record's Weight resolves to record 0's value:
Weight truth=1.0 legacy=0.3
Points truth=10000 legacy=4000
Weight truth=3.3 legacy=0.3
Points truth=15000 legacy=4000
0.3 and 4000 are record 0's values, returned for every record after it.
What this means for the corpus
- A number read with
get_f32from a single-record object is safe — the diff found no counterexample in 29 822 fields. - A number read from a multi-record object is safe only for the first record; every later record has a ~18 % chance of being record 0's value.
- The
Nonebucket (43 %) is the guard working as designed:get_f32rejects a non-numeric neighbour rather than inventing a value, so a defaulted field reads as absent instead of wrong.
⚠️ A first pass that measured the wrong thing
My first sweep compared the truth against "the string immediately preceding this
field's own key in the pool" and reported 65.90 % disagreement. That number
is not the legacy reader's error rate, because it is not what get_raw does —
get_raw uses the first occurrence of the key anywhere in the object, not
this field's own key. The 65.90 % figure is withdrawn; 17.54 % is the measured
one, and the is_definite_value guard is why it is so much lower.
The lesson is the same one this corpus keeps paying for: before measuring how wrong a tool is, read what the tool actually does.