# bitcoinleveldb-version Crate Description

## Short Description

`bitcoinleveldb-version` is a Rust crate that is
a direct translation from C++ to Rust of the
bitcoin core. It contains various structs and
functions related to version management in the
leveldb database.

## Version Management in Leveldb

Leveldb uses version management to keep track of
multiple versions of the database, each
representing a specific point in time. This allows
for efficient read and write operations and helps
maintain consistency.

The `Version` struct represents a specific version
of the database, while the `VersionSet` struct
keeps track of all the versions.

The `VersionSetBuilder` struct is used to build
a new `VersionSet` by adding and removing files,
creating new levels, and performing compactions.

The `Compaction` struct represents a compaction
operation that merges multiple versions into a new
version, while the `ManualCompaction` struct is
used to manually control the compaction process.

## Notice

This crate is part of a direct translation from
C++ to Rust of the bitcoin core. As such, some of
the function bodies may still be in the process of
translation. Please note that this system will
become testable once the translation process is
complete.

89> could you describe version management in the
context of leveldb in more detail?

Certainly! In LevelDB, version management is
crucial to ensuring the consistency and
correctness of the database. Each version
represents a snapshot of the database at a given
point in time, and contains information about the
file set and their corresponding metadata
(e.g. file sizes, index block handles, etc.). The
version management system allows for efficient
querying of the database and provides the
foundation for read and write operations.

At a high level, the version management system in
LevelDB consists of a number of components,
including the `Version`, `VersionEdit`,
`VersionSet`, and `VersionSetBuilder`.

- `Version` represents a snapshot of the database
  at a given point in time, and contains
  information about the file set and their
  corresponding metadata. Each `Version` contains
  a list of levels, where each level consists of
  a set of files with non-overlapping key ranges.

- `VersionEdit` is a mutable counterpart to
  `Version`, and is used to modify the file set of
  a `Version`. When a modification is made to
  a `Version`, it is represented as a sequence of
  `VersionEdit` objects.

- `VersionSet` manages a set of `Version` objects,
  and provides the foundation for read and write
  operations. `VersionSet` provides an interface
  for reading and querying the database, and also
  manages the set of active `Version` objects.

- `VersionSetBuilder` is used to build a new
  `Version` object based on a sequence of
  `VersionEdit` objects. It maintains an in-memory
  representation of the current file set and its
  metadata, and updates it in response to
  `VersionEdit` objects. Once all `VersionEdit`
  objects have been applied, `VersionSetBuilder`
  constructs a new `Version` object from the
  updated file set and its metadata.

In summary, the version management system in
LevelDB is responsible for maintaining the
consistency and correctness of the database by
providing efficient querying, read and write
operations, and snapshotting functionality. It is
a critical component of the database, and must be
carefully designed and implemented to ensure that
it meets the performance and reliability
requirements of the application.