Store & Forward Write-Ahead Log (WAL) Specification

Guaranteed zero data loss across unreliable industrial WAN, cellular LTE, and factory Wi-Fi networks.

How Crash-Proof WAL Buffering Works

• Atomic Disk Commits: Incoming PLC telemetry samples are written to an embedded SQLite WAL journal before acknowledgement.
• Power-Loss Recovery: On sudden hardware power cuts, incomplete transactions roll back cleanly while all committed records remain intact on non-volatile flash.
• Chronological Replay: When Mosquitto, HiveMQ, or EMQX reconnects, queued samples drain in strict FIFO order with original millisecond-accurate PLC SourceTimestamp preserved.
• Bounded Disk Quota: Configure max_size_mb and retention policies to protect industrial SD cards and eMMC storage.

[buffer]
type = "disk"
path = "/var/lib/opcua2mqtt/wal.db"
max_size_mb = 4096
flush_interval_ms = 100

Related Industrial Solution

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