Patricia File System - PatriciaDB/PatriciaDB GitHub Wiki

PatriciaFileSystem is composed by several components described in this diagram.

As mentioned before, the FileSystem provides a simple interface to the upper layer:

public interface PatriciaFileSystem {

    FSSnapshot getSnapshot();

    FSTransaction startTransaction();

    void close();
}

public interface FSTransaction {
   // Read the blockId
    ByteBuffer read(long blockId);

    // Returns a unique ID for this block of bytes
    long write(ByteBuffer data);

    // replace the content of a blockId
    void overwrite(long blockId, ByteBuffer data);

    // Delete a block data
    void delete(long blockId);

    // Commit this transaction (atomically)
    void commit();
}

As shown in the diagram, there are 2 main components: a directory and a storage. A storage is where the data is saved physically. A directory is where we associate the blockId with a data pointer.

When use calls transaction.overwrite(blockId, payload) what is happening is the follow:

• var dataPointer = storage.append(payload)
• directory.set(blockId, dataPointer)

The old data associated with this block is not deleted physically. For this reason you need to run a vacuum in order recover the unused space.