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    Storage: Directory Structure

    On-disk Data Structure

    • The on-disk structure of RavenDB data directories is as follows:

    • <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

    • The main <data-dir> contains:

      • Databases folder
        Contains subdirectories with data per database.
      • System folder
        Stores cluster data & server-wide data such as shared resources needed by all cluster nodes,
        e.g. the Database Record.

    • The System folder, the Database folders, and their inner folders (the Configuration folder and each Index folder) are each a separate Voron storage environment.

    Voron Storage Environment

    • Each Voron storage environment is composed of:

    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.

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