LogStore Class

Definition

Namespace:

System.IO.Log

Assembly:

System.IO.Log.dll

Represents a log-structured storage.

public ref class LogStore sealed : IDisposable

public sealed class LogStore : IDisposable

type LogStore = class
    interface IDisposable

Public NotInheritable Class LogStore
Implements IDisposable

Inheritance

Object

LogStore

Implements

IDisposable

Examples

The following example shows how to archive a LogStore to an XML document.

class LogBackup
{
    static void ArchiveToXML(LogStore logStore, string fileName)
    {
        LogArchiveSnapshot snapshot = logStore.CreateLogArchiveSnapshot();

        XmlTextWriter writer = new XmlTextWriter(fileName, Encoding.ASCII);

        writer.WriteStartElement("logArchive");
        foreach(FileRegion region in snapshot.ArchiveRegions)
        {
            writer.WriteStartElement("fileRegion");
            writer.WriteElementString("path", region.Path);
            writer.WriteElementString("length", region.FileLength.ToString());
            writer.WriteElementString("offset", region.Offset.ToString());
            using(Stream dataStream = region.GetStream())
            {
                byte[] data = new byte[dataStream.Length];
                dataStream.Read(data, 0, data.Length);
                writer.WriteElementString("data", Convert.ToBase64String(data));
            }
            writer.WriteEndElement();
        }
        writer.WriteEndElement();
        writer.Close();
        logStore.SetArchiveTail(snapshot.LastSequenceNumber);
    }
    static void RestoreFromXML(string fileName)
    {
        using(XmlTextReader reader = new XmlTextReader(fileName))
        {
            reader.ReadStartElement("logArchive");
            while(reader.IsStartElement())
            {
                string path = reader.ReadElementString("path");
                long length = Int64.Parse(reader.ReadElementString("length"));
                long offset = Int64.Parse(reader.ReadElementString("offset"));
                string dataString = reader.ReadElementString("data");
                byte[] data = Convert.FromBase64String(dataString);
                FileStream fileStream;
                using(fileStream = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    fileStream.SetLength(length);
                    fileStream.Position = offset; fileStream.Write(data, 0, data.Length);
                }
            }
        reader.ReadEndElement();
        }
    }
}

Friend Class LogBackup
    Private Shared Sub ArchiveToXML(ByVal logStore As LogStore, ByVal fileName As String)
        Dim snapshot As LogArchiveSnapshot = logStore.CreateLogArchiveSnapshot()

        Dim writer As New XmlTextWriter(fileName, Encoding.ASCII)

        writer.WriteStartElement("logArchive")
        For Each region As FileRegion In snapshot.ArchiveRegions
            writer.WriteStartElement("fileRegion")
            writer.WriteElementString("path", region.Path)
            writer.WriteElementString("length", region.FileLength.ToString())
            writer.WriteElementString("offset", region.Offset.ToString())
            Using dataStream As Stream = region.GetStream()
                Dim data(dataStream.Length - 1) As Byte
                dataStream.Read(data, 0, data.Length)
                writer.WriteElementString("data", Convert.ToBase64String(data))
            End Using
            writer.WriteEndElement()
        Next region
        writer.WriteEndElement()
        writer.Close()
        logStore.SetArchiveTail(snapshot.LastSequenceNumber)

    End Sub
    Private Shared Sub RestoreFromXML(ByVal fileName As String)
        Using reader As New XmlTextReader(fileName)
            reader.ReadStartElement("logArchive")
            Do While reader.IsStartElement()
                Dim path = reader.ReadElementString("path")
                Dim length = Int64.Parse(reader.ReadElementString("length"))
                Dim offset = Int64.Parse(reader.ReadElementString("offset"))
                Dim dataString = reader.ReadElementString("data")
                Dim data() = Convert.FromBase64String(dataString)
                Dim fileStream As FileStream
                fileStream = New FileStream(path, FileMode.OpenOrCreate, FileAccess.Write)
                Using fileStream
                    fileStream.SetLength(length)
                    fileStream.Position = offset
                    fileStream.Write(data, 0, data.Length)
                End Using
            Loop
            reader.ReadEndElement()
        End Using
    End Sub
End Class

Remarks

The LogRecordSequence class provides an implementation of the record sequence interface on top of a Common Log File System (CLFS) log. It works with the LogStore class, which provides an interface for directly manipulating and managing a CLFS log file. A log store provides append-only storage across a set of disk extents. The LogStore class represents this storage, and provides methods for adding and removing containers, setting policy, and creating archives. It does not provide methods for reading from and writing to the storage; these methods are provided by the LogRecordSequence class.

The relationship between the LogStore class and the LogRecordSequence class is similar to the relationship between a disk file and a FileStream object. The disk file provides the actual storage and has attributes such as length and last access time, while the FileStream object provides a view on the file that can be used to read from it and write to it. Similarly, the LogStore class has attributes like a policy and a collection of disk extents, and the LogRecordSequence class provides a record-oriented mechanism for reading and writing data.

Unlike the file record sequence represented by the FileRecordSequence class, a LogStore instance stores its data in a collection of disk extents, represented by LogExtent instances. The extents in a given LogStore instance are all of uniform size, and space is added to and removed from a LogStore instance in extent increments. To add and remove log extents, use the Add and Remove methods of the LogExtentCollection object, which can be returned by the Extents property.

A LogStore instance can have policies associated with it. These are represented by LogPolicy instances that can be returned by the Policy property. A policy dictates rules that the log will attempt to follow, such as maximum number of extents and minimum size, and instructions on growing or shrinking the LogStore under certain conditions. In addition, you can specify whether a LogStore instance can be archived. Policies are set per log and are volatile, which means that once every handle to the log is closed, the policy no longer exists.

Constructors

LogStore(SafeFileHandle)	Initializes a new instance of the LogStore class for the specified handle.
LogStore(String, FileMode, FileAccess, FileShare, FileSecurity)	Initializes a new instance of the LogStore class.
LogStore(String, FileMode, FileAccess, FileShare)	Initializes a new instance of the LogStore class.
LogStore(String, FileMode, FileAccess)	Initializes a new instance of the LogStore class with the specified path, mode, and access.
LogStore(String, FileMode)	Initializes a new instance of the LogStore class with the specified path and mode.

Properties

Archivable	Gets a value indicating whether this LogStore instance can be archived.
BaseSequenceNumber	Gets the lowest sequence number that corresponds to a valid record in this LogStore instance.
Extents	Gets the collection of log extents that contain the data for this log store.
FreeBytes	Gets the number of bytes available in the log store.
Handle	Gets the operating system file handle for the log file that the current LogStore instance encapsulates.
LastSequenceNumber	When overridden in a derived class, gets the sequence number of the next record to be appended to the log store.
Length	Gets the size of the log store, in bytes.
Policy	Gets the policy associated with this log store.
StreamCount	Gets the number of log streams in this log store.

Methods

CreateLogArchiveSnapshot()	Takes a snapshot of the log store state for making a backup.
CreateLogArchiveSnapshot(SequenceNumber, SequenceNumber)	Takes a snapshot of the log store state between the specified sequence numbers for making a backup.
Delete(String)	Removes the log store.
Dispose()	Releases all resources used by the LogStore.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
SetArchiveTail(SequenceNumber)	Sets the sequence number of the archive tail.
ToString()	Returns a string that represents the current object. (Inherited from Object)