Storage: Directory Structure

• <data-dir>
  • Databases
    • <database-name>
      • Confguration
        • Journals
        • Temp
        • Raven.voron
      • Indexes
        • <index-name>
          • Journals
          • Temp
          • Raven.voron
        • ...more indexes
      • Journals
      • Temp
      • Raven.voron
    • ...more databases
  • System
    • Journals
    • Temp
    • Raven.voron

Temp Folder

• Holds temporary scratch & compression *.buffers files.
• These are small memory-mapped files that keep separate data versions for concurrent running transactions.
• Data modified by a transaction is copied into the scratch space - modifications are made on a copy of the data.
• Compression files are used to compress the transaction data just before writing it to the journal.
• When a transaction is written from these files to the journal file it is considered committed.

Journals Folder

• Contains Write-Ahead Journal files (WAJ) that are used in the hot path of a transaction commit.
• From the journals, transactions will be flushed to the Voron data file where they are persisted.

• Entries written to these files use unbuffered sequential writes and direct I/O to ensure a direct write that bypasses all caches.
• Writes to the journals happen immediately, have high priority, and take precedence over writes to the Voron data file.

• Data is cleared from the journals once it is successfully stored in the Voron data file.
• The journal's transactions take part in database recovery - info is used to recover up to the same point you were at before failure.
  

Raven.voron file

• This file contains the persisted data on disk.
• It is a memory-mapped data file using buffered writes with random reads and writes.