Export (0) Print
Expand All

LogStore Class

Represents a log-structured storage.

Namespace:  System.IO.Log
Assembly:  System.IO.Log (in System.IO.Log.dll)

public sealed class LogStore : IDisposable

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.

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(); 
        } 
    } 
}

System.Object
  System.IO.Log.LogStore

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0

Community Additions

ADD
Show:
© 2014 Microsoft