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Interview concept

What is a write-ahead log?

A write-ahead log, or WAL, appends a description of each change to durable storage before the database updates its main data pages. After a crash, the database replays committed records and ignores incomplete work to restore a consistent state.

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Summary

Key takeaways

Write-Ahead Logging in Databases - ExtraBrain is part of ExtraBrain's local-first Mac workflow for live interviews, meetings, transcription, provider control, and responsible AI use.

Page focus

A write-ahead log, or WAL, appends a description of each change to durable storage before the database updates its main data pages. After a crash, the database replays committed records and ignores incomplete work to restore a consistent state.

Platform fact

ExtraBrain has 1 current public platform family, macOS, with support for 2 Mac CPU families: Apple Silicon and Intel.

Data-flow fact

ExtraBrain has 3 configurable data paths to review before sensitive work: local Parakeet transcription, local Gemma 4 where installed and compatible, and external providers you choose.

Interview concept

How it works

Log before data

The database must flush the relevant log record before acknowledging a commit whose data pages are not yet durable.

Sequential I/O

Appending to a log is more efficient than synchronously writing many scattered data pages for every transaction.

Crash recovery

Checkpoints limit how far recovery must scan, while redo and undo rules reconstruct committed state and discard incomplete transactions.

Replication source

Replicas can consume an ordered WAL stream, though physical and logical formats expose different levels of detail.

Interview concept

Practice the tradeoffs with ExtraBrain

Narrate a crash boundary

Mark log flush, commit acknowledgement, and page write on a timeline while ExtraBrain captures exactly which records recovery must replay.

Keep database internals practice local

Mac-native local transcription and local session history support private review without sending every technical rehearsal to a hosted service.

Choose how to analyze it

Use compatible on-device AI or a provider you bring for critique. The free core also acts as a meeting copilot in database study sessions.

Interview concept

Responsible use

Use any live AI assistant only where interview, workplace, school, and platform rules allow it. Do not use generated answers to misrepresent your skills, experience, or authorship.

FAQ

Common questions.

Short answers for people and crawlers comparing ExtraBrain with other live AI assistants.

Why must the log be written before data pages?

If a crash happens before dirty pages reach disk, the durable log still contains enough information to replay committed changes.

What is a database checkpoint?

A checkpoint records a recovery position and coordinates page flushing so startup does not need to scan the log from the beginning.

Is a WAL the same as an event log?

No. A WAL is an internal recovery structure, while a domain event log captures business facts intended for application-level consumption.