3.0.0

3.0.0 - 2025-08-09

Removes support for file format v2.

Use Database::upgrade(), in redb 2.6, to migrate to the v3 file format.

General storage optimizations

The v3 file format has been further optimized to reduce the size of the database. Databases with only
a few small keys will see the largest benefit, and the minimum size of a database file has decreased
from ~2.5MiB to ~50KiB. To achieve the smallest file size call Database::compact() before
dropping the Database.

Additionally, performance is ~15% better in bulk load benchmarks. This was achieved by implementing
a custom hash function for various in-memory HashSets and HashMaps, and by optimizing the usage
of buffers held in Arcs to reduce the number of atomic instructions executed.

Optimize storage of tuple types

Storage of variable width tuple types with arity greater than 1 is more efficient. The new format
elides the length of any fixed width fields and uses varint encoding for the lengths of all variable
width fields.

Note that this encoding is not compatible with the serialization of variable width tuples used in prior versions.
To load tuple data created prior to version 3.0, wrap them in the Legacy type.
For example, TableDefinition<u64, (&str, u32)> becomes TableDefinition<u64, Legacy<(&str, u32)>>.
Fixed width tuples, such as (u32, u64) are backwards compatible.

Derive for Key and Value traits

Key and Value can be derived using the redb-derive crate. Note that it does not support
schema migration. The recommended pattern to migrate schema is to create a new table, and then
perform a migration from the old table to the new table.

Read-only multi-process support

Multiple processes may open the same database file for reading by using the new ReadOnlyDatabase
type. On platforms which support file locks, this acquires a shared lock on the database file.

Enable garbage collection in Durability::None transactions

Non-durable transactions will now free pages when possible (pages allocated in a preceding
non-durable transaction which are no longer referenced).
This resolves an issue where a long sequence of non-durable transactions led to significant growth
in the size of the database file.
This change increases the RAM required for a sequence of non-durable transactions, such that RAM
proportional to the net change in the database is now used. However, it will never use more than
about 0.2% of the database file size.

Other changes

• Add ReadOnlyDatabase
• Add Builder::open_read_only()
• Add StorageBackend::close()
• Add Table::get_mut()
• Add chrono_v0_4 feature flag which enables serialization of the NaiveDate, NaiveTime,
  NaiveDatetime, DateTime<FixedOffset>, and FixedOffset types in the chrono crate
• Add uuid feature flag which enables serialization of the Uuid type in the uuid crate
• Change StorageBackend::read() to accept a &mut [u8] output argument instead of returning
  a Vec<u8>
• Change Table::insert_reserve() to take usize instead of u32 as the argument type
• Change TypeName::name() to be public
• Change ReadTransactionStillInUse to contain a Box
• Change set_durability() to return a Result
• Move Database::cache_stats() and Database::begin_read() to ReadableDatabase trait
• Rename AccessGuardMut to AccessGuardMutInPlace. Note that a new AccessGuardMut struct has
  been added; it serves a different purpose
• Remove Durability::Paranoid
• Fix a rare case where check_integrity() returned Ok(false) even though no repair was required,
  when called on a database that was not shutdown cleanly and was automatically repaired when opened
• Disallow access to the database from read transactions after the Database as been
  dropped. Access will now return DatabaseClosed