[Variant] Converting variant to JSON string seems slow #7869
Description
I added several timestamp markers (std::time::Instant::elapsed) to the test_json_to_variant_object_very_large test and ran with cargo test --release:
| elapsed time (ms) | delta (ms) | finished step |
|---|---|---|
| 5 | 5 | generate data structures and json string |
| 250 | 245 | json_to_variant |
| 593 | 343 | Variant::try_new |
| 1758 | 1165 | variant_to_json_string |
| 1839 | 81 | build variant directly |
| 2171 | 332 | Variant::try_new |
| 2758 | 587 | JsonToVariantTest::run |
We can build up the raw data structures and directly create a JSON string from them in 5ms, and parse the JSON string to a variant value in ~250ms, but it somehow takes 1.1 seconds to convert the resulting variant back to a string. Something seems wrong here.
Variant::try_new also seems quite slow (330-340 ms).