bitcoinleveldb-meta crate description

This crate provides functionality related to the metadata management in the LevelDB key-value store.

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."

Tokens:

• Saver
• SaverState
• after_file
• before_file
• expanded_compaction_byte_size_limit
• find_file
• find_smallest_boundary_file
• get_file_iterator
• max_bytes_for_level
• max_file_size_for_level
• max_grand_parent_overlap_bytes
• save_value
• some_file_overlaps_range
• total_file_size
• AddBoundaryInputsTest
• FindFileTest
• add
• create_file_meta_data
• dbversion_set_test_main
• default
• drop
• find
• find_file_test_empty
• find_file_test_multiple
• find_file_test_multiple_null_boundaries
• find_file_test_overlap_sequence_checks
• find_file_test_overlapping_files
• find_file_test_single
• overlaps
• Tag
• get_internal_key
• get_level

The metadata management in LevelDB handles various properties of the underlying database files such as their size, location, and range of keys they cover. This crate provides functions to locate files in the database, calculate their size, and detect overlapping files. It also provides tools to set limits on the size of files in different levels of the database, as well as limits on the total size of the database.

The crate implements a Saver interface for iterating over database files, and a SaverState structure that tracks the progress of the iteration. The crate also provides functions to create file metadata and determine their level based on their size.

In addition, the crate includes test functions for finding database files and detecting overlapping files.

Note that this crate is still in the process of being translated from C++ to Rust, so some functions may not yet be available. Once the translation process is complete, this crate will become fully testable.

59> which metadata do we track in leveldb?

In LevelDB, metadata is tracked for each file that stores key-value pairs. This metadata includes the file number, file size, file creation time, file modification time, the smallest and largest key stored in the file, the largest sequence number of the entries in the file, and a flag indicating whether the file has been marked for compaction.

LevelDB also tracks metadata about the entire database, such as the current database version, the maximum file size, the number of levels in the database, the size ratio between levels, and the target file size for each level. This metadata is stored in the "MANIFEST" file, which is a log-structured file that records changes to the database metadata over time.

60> thanks -- how else do we use metadata in this system?

Metadata plays an important role in LevelDB for various purposes such as:

1. Version management: LevelDB maintains a version set that stores metadata for all versions of the database. This metadata includes the current version, the previous version, and a list of all versions. The version set helps to track changes to the database over time and facilitates compaction and garbage collection.

2. File management: LevelDB uses metadata to manage files in the database. For example, it tracks the file number, file size, and creation time of each file. This information is used to perform operations such as file deletion, file opening, and file iteration.

3. Indexing: LevelDB uses metadata to index keys in the database. The metadata includes information about the location of keys and the mapping of keys to their associated values. This information is used to perform operations such as key lookups, range scans, and compaction.

4. Compression: LevelDB uses metadata to track compression information for files in the database. The metadata includes information such as the compression algorithm used and the compression ratio achieved. This information is used to optimize compression and decompression performance and to ensure data integrity.

Overall, metadata is a crucial component of the LevelDB system that enables efficient and effective management of data and resources.