# Description
This PR renames the conversion functions on `Value` to be more consistent.
It follows the Rust [API guidelines](https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv) for ad-hoc conversions.
The conversion functions on `Value` now come in a few forms:
- `coerce_{type}` takes a `&Value` and attempts to convert the value to
`type` (e.g., `i64` are converted to `f64`). This is the old behavior of
some of the `as_{type}` functions -- these functions have simply been
renamed to better reflect what they do.
- The new `as_{type}` functions take a `&Value` and returns an `Ok`
result only if the value is of `type` (no conversion is attempted). The
returned value will be borrowed if `type` is non-`Copy`, otherwise an
owned value is returned.
- `into_{type}` exists for non-`Copy` types, but otherwise does not
attempt conversion just like `as_type`. It takes an owned `Value` and
always returns an owned result.
- `coerce_into_{type}` has the same relationship with `coerce_{type}` as
`into_{type}` does with `as_{type}`.
- `to_{kind}_string`: conversion to different string formats (debug,
abbreviated, etc.). Only two of the old string conversion functions were
removed, the rest have been renamed only.
- `to_{type}`: other conversion functions. Currently, only `to_path`
exists. (And `to_string` through `Display`.)
This table summaries the above:
| Form | Cost | Input Ownership | Output Ownership | Converts `Value`
case/`type` |
| ---------------------------- | ----- | --------------- |
---------------- | -------- |
| `as_{type}` | Cheap | Borrowed | Borrowed/Owned | No |
| `into_{type}` | Cheap | Owned | Owned | No |
| `coerce_{type}` | Cheap | Borrowed | Borrowed/Owned | Yes |
| `coerce_into_{type}` | Cheap | Owned | Owned | Yes |
| `to_{kind}_string` | Expensive | Borrowed | Owned | Yes |
| `to_{type}` | Expensive | Borrowed | Owned | Yes |
# User-Facing Changes
Breaking API change for `Value` in `nu-protocol` which is exposed as
part of the plugin API.
# Description
Currently, the `into sqlite` command collects the entire input stream
into a single Value, which soaks up the entire input into memory, before
it ever tries to write anything to the DB. This is very problematic for
large inputs; for example, I tried transforming a multi-gigabyte CSV
file into SQLite, and before I knew what was happening, my system's
memory was completely exhausted, and I had to hard reboot to recover.
This PR fixes this problem by working directly with the pipeline stream,
inserting into the DB as values are read from the stream.
In order to facilitate working with the stream directly, I introduced a
new `Table` struct to store the connection and a few configuration
parameters, as well as to make it easier to lazily create the table on
the first read value.
In addition to the purely functional fixes, a few other changes were
made to the serialization and user facing behavior.
### Serialization
Much of the preexisting code was focused on generating the exact text
needed for a SQL statement. This is unneeded and less safe than using
the `rusqlite` crate's serialization for native Rust types along with
prepared statements.
### User-Facing Changes
Currently, the command is very liberal in the input types it accepts.
The strategy is basically if it is a record, try to follow its structure
and make an analogous SQL row, which is pretty reasonable. However, when
it's not a record, it basically tries to guess what the user wanted and
just makes a single column table and serializes the value into that one
column, whatever type it may be.
This has been changed so that it only accepts records as input. If the
user wants to serialize non-record types into SQL, then they must
explicitly opt into doing this by constructing a record or table with it
first. For a utility for inserting data into SQL, I think it makes more
sense to let the user choose how to convert their data, rather than make
a choice for them that may surprise them.
However, I understand this may be a controversial change. If the
maintainers don't agree, I can change this back.
#### Long switch names
The `file_name` and `table_name` long form switches are currently
snake_case and expect to be as such at the command line. These have been
changed to kebab-case to be more conventional.
# Tests + Formatting
To test the memory consumption, I used [this publicly available index of
all Wikipedia articles](https://dumps.wikimedia.org/enwiki/20230820/),
using the first 10,000, 100,000, and 1,000,000 entries, in that order. I
ran the following script to benchmark the changes against the current
stable release:
```nu
#!/usr/bin/nu
# let shellbin = $"($env.HOME)/src/nushell/target/aarch64-linux-android/release/nu"
let shellbin = "nu"
const dbpath = 'enwiki-index.db'
[10000, 100000, 1000000]
| each {|rows|
rm -f $dbpath;
do { time -f '%M %e %U %S' $shellbin -c (
$"bzip2 -cdk ~/enwiki-20230820-pages-articles-multistream-index.txt.bz2
| head -n ($rows)
| lines
| parse '{offset}:{id}:{title}'
| update cells -c [offset, id] { into int }
| into sqlite ($dbpath)"
)
}
| complete
| get stderr
| str trim
| parse '{rss_max} {real} {user} {kernel}'
| update cells -c [rss_max] { $"($in)kb" | into filesize }
| update cells -c [real, user, kernel] { $"($in)sec" | into duration }
| insert rows $rows
| roll right
}
| flatten
| to nuon
```
This yields the following results
Current stable release:
|rows|rss_max|real|user|kernel|
|-|-|-|-|-|
|10000|53.6 MiB|770ms|460ms|420ms|
|100000|209.6 MiB|6sec 940ms|3sec 740ms|4sec 380ms|
|1000000|1.7 GiB|1min 8sec 810ms|38sec 690ms|42sec 550ms|
This PR:
|rows|rss_max|real|user|kernel|
|-|-|-|-|-|
|10000|38.2 MiB|780ms|440ms|410ms|
|100000|39.8 MiB|6sec 450ms|3sec 530ms|4sec 160ms|
|1000000|39.8 MiB|1min 3sec 230ms|37sec 440ms|40sec 180ms|
# Note
I started this branch kind of at the same time as my others, but I
understand the feedback that smaller PRs are preferred. Let me know if
it would be better to split this up.
I do think the scope of the changes are on the bigger side even without
the behavior changes I mentioned, so I'm not sure if that will help this
particular PR very much, but I'm happy to oblige on request.
