File-Based Session Storage

File-Based Session Storage keeps incoming and outgoing messages and session's state data in files in the StorageDirectory folder.

For each iLink 3 session, the following files are created:

SESSION_NAME is formed on the base of Uuid, Firm, MarketSegmentId, and a timestamp. It is available via the StorageId property.

Segmented File-Based Storage

Sometimes it is needed to save space on disk, and there is no need to keep the whole history of incoming and outgoing messages. File-Based Storage could be configured to store messages in a set of .summary files, instead of a single one. The entire collection of logged messages is split through several files called "segments", and older segments could be archived.

The Segmented mode of the File-based Storage is activated when the FileBasedStorageSegmentSize is set to a positive value.

Segments are named as StorageID[-part-N].summary, where:

  • StorageID- the generic ID of storage (available via the StorageId property);
  • -part-N- the segment suffix. The N is the 1-based number of segments. One segment does not have this suffix - it is the segment where the newest messages are stored.

During the session lifetime, new segment files are created per the following algorithm:

  • A new message is saved to the StorageID.summary file;
  • When the message is saved, the StorageID.summary file size is compared to the FileBasedStorageSegmentSize value, and if the actual file size exceeds this value, a new segment is created;
  • To create a new segment, the Handler renames StorageID.summary to StorageID-part-N.summary and creates a new empty StorageID.summary file to store subsequent messages. The N is a sequential number of parts starting from 1.

So during a long session, a set of files could be created: StorageID.summary, StorageID-part-1.summary, StorageID-part-2.summary, etc. . Oldest messages are stored in the StorageID-part-1.summary file, and newer ones - in the StorageID.summary and StorageID-part-N.summary files, where N is the maximum value.

The number of segments is recorded in the StorageID.state file after the FilePartCount key. For instance, if there are 5 segments, (StorageID.summary, StorageID-part-1.summary, ... , StorageID-part-4.summary) the following line will be stored in the StorageID.state file:

FilePartCount=5

Examples

File-Based Storage without segmentation

SessionSettings settings = new ();

using Session session = new(settings, marketSegmentId, SessionStorageType.FileBasedStorage);

Segmented storage


SessionSettings settings = new()
{
    FileBasedStorageSegmentSize = 256 * 1024
};

using Session session = new (settings, marketSegmentId, SessionStorageType.FileBasedStorage);