* Make `Page` always fully init
Per discussion on the snapshotting proposal,
this PR changes the type of `Page.row_data` to `[u8; _]`,
where previously it was `[MaybeUninit<u8>; _]`.
This turns out to be shockingly easy,
as our serialization codepaths never write padding bytes into a page.
The only place pages ever became `poison` was the initial allocation;
changing this to `alloc_zeroed` causes the `row_data` to always be valid at `[u8; _]`.
The majority of this diff is replacing `MaybeUninit`-specific operators
with their initialized equivalents,
and updating comments and documentation to reflect the new requirements.
This change also revealed a bug in the benchmarks
introduced when we swapped the order of sum tags and payloads
( https://github.com/clockworklabs/SpacetimeDB/pull/1063 ),
where benchmarks used a hardcoded offset for the tag which had not been updated.
* Update blake3
Blake3 only supports running under Miri as of 1.15.1, the latest version.
Prior versions hard-depended on SIMD intrinsics which Miri doesn't support.
* Address Mazdak's review.
Still pending his agreeing with me that `poison` is a better name than `uninit`.
* "Poison" -> "uninit"
Against my best wishes, for consistency with the broader Rust community's poor choices.
* Remove unnecessary `unsafe` blocks
* More unnecessary `unsafe`; remove forgotten SAFETY comments
2. Make `RowRef::row_hash` use the above.
3. Make `Table::insert` return a `RowRef`.
4. Use less unsafe because of 1-3.
5. Use `second-stack` to reuse temporary allocations in hashing and serialization.
`AlgebraicTypeLayout` and friends already include full layout information,
including properly-aligned offsets for `ProductTypeElementLayout`s.
As such, there's no need to do any alignment computation
during `serialize_value` or `write_value`.
Instead, while traversing a `ProductTypeLayout`,
we can use each element's `offset` to update the `curr_offset`.
This commit defines `trait ReadColumn`,
which is implemented for types that can be stored in a table column
and can be read out of said table column.
Its interesting method is
`read_column(row: RowRef<'_>, idx: usize) -> Result<Self, TypeError>`,
which attempts to read the `idx`th column of `row` as a value of type `Self`,
returning a `TypeError` if the row in question does not have the appropriate types.
`ReadColumn` is implemented for Rust equivalents of all non-compound `AlgebraicType`s,
i.e. integers, floats, `bool` and `String`.
It is also implemented for all SATS value types,
including those which represent values of compound types,
i.e. `AlgebraicValue`, `ProductValue`, `SumValue`, `ArrayValue` and `MapValue`.
Mazdak Farrokhzad