Principle:Apache Paimon Snapshot Management

Knowledge Sources	Apache_Paimon
Domains	Storage, Versioning
Last Updated	2026-02-08 00:00 GMT

Overview

Immutable snapshot-based versioning of table state that enables time-travel queries, consistent reads, and atomic commits through a sequence of point-in-time views.

Description

Snapshot management provides a foundational versioning mechanism for data lakes and table formats where each write operation creates a new immutable snapshot representing the complete state of the table at a specific point in time. Rather than modifying data in place, every commit generates a new snapshot that references the data files comprising that version. This immutability enables powerful capabilities including time-travel queries, rollback operations, and consistent concurrent reads without locking.

Each snapshot contains metadata about the commit including timestamp, schema version, manifest lists, statistics, and lineage information linking it to previous snapshots. The snapshot manager maintains the sequence of snapshots and provides efficient lookup by snapshot ID or timestamp. Snapshots form a timeline where readers can select any historical version while writers append new snapshots atomically using techniques like atomic file creation or optimistic concurrency control.

The snapshot commit process ensures atomicity by writing all metadata files first, then atomically publishing the new snapshot as the current table version. If the commit fails at any point, partial writes are simply abandoned without affecting the visible table state. This approach eliminates the need for distributed transactions while still providing ACID guarantees at the table level. Snapshot retention policies determine how long historical versions are preserved before being eligible for garbage collection.

Usage

Apply this principle when building table formats that require consistent point-in-time reads, audit trails, or the ability to query historical data states. Use snapshot-based versioning when multiple readers and writers need to access the table concurrently without coordination, or when atomic commits spanning multiple files are required without distributed transactions.

Theoretical Basis

The snapshot management pattern implements a versioned object store where each version is immutable and addressable. The core algorithm follows:

Snapshot Creation:

Prepare new data files (append, compact, or reorganize existing files)
Generate manifest files listing all data files in this version
Create snapshot metadata containing:

 - Unique snapshot ID (monotonically increasing)
 - Commit timestamp
 - Schema version identifier
 - Manifest list reference
 - Statistics summary (record count, file count, data size)
 - Parent snapshot ID for lineage

Atomic Commit Protocol:

Write all data files to storage
Write manifest files referencing data files
Write snapshot metadata file with unique name (snapshot-N)
Atomically update current pointer to new snapshot ID
If pointer update fails (conflicting concurrent write), retry or abort

Snapshot Lookup:

Latest snapshot: Read current pointer
By ID: Direct lookup of snapshot-N file
By timestamp: Binary search through snapshot timeline
Time-travel: Find latest snapshot with timestamp <= query_time

Snapshot Expiration:

Keep snapshots newer than retention threshold
Mark older snapshots as expired
Identify data files referenced only by expired snapshots
Delete unreferenced files in garbage collection phase

The immutability guarantee ensures that once a snapshot is visible, its content never changes, enabling lock-free concurrent reads while writers create new snapshots independently.

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