A beginner's guide to the Git reftable format

Introduction

This guide provides an overview of the Git reftable format, introduced in Git 2.45.0, for storing references efficiently.

High-level structure of reftables

• Git repositories can be initialized with the "reftable" format to store references in individual files.
• The references are stored in the refs directory, with reftable containing a table of references and reflog data in binary format.
• Records in the reftable file have keys for reference names and point to object IDs or other references, along with old and new object IDs and message for reflog entries.

Sections in reftables

• Sections in reftables contain sorted records based on keys, enabling efficient lookup of references.
• Records within sections share a common prefix, allowing for prefix compression to reduce storage space.

Binary search for reference lookup

• Binary search is used to find the block containing the reference, followed by a linear search within the block to locate the specific record.
• Restart points in the reftable format aid in optimizing reference lookups within blocks.

By understanding the structure and mechanisms of the Git reftable format, users can efficiently manage and access references within repositories.