<filesystem>

When this tag is present, the topic data will be persisted into files.

See Table 75.4 Filesystem tags.

<restore>

This DDS_Boolean (see 75.2.1 Configuration File Syntax) indicates if the topic data associated with a previous execution of the persistence service must be restored or not. If the topic data is not restored, it will be deleted from the persistent storage.

Restoring the topic data associated with a previous execution of the Persistence Service requires you to do the following:

• Use the same <persistence_service> configuration name (-cfgName; see 76.1 Starting the Persistence Service Executable) that was used to persist the data.
• For each <participant> (see 75.7 Configuring Participants) whose topic data should be restored, use the same name attribute in XML as the previous execution that persisted the data. By default this attribute is set to a random anonymous value. For persisted data to be restored, you must explicitly set this value to the same string.

Default: true

<directory>

Specifies the directory of the files in which topic data will be persisted. There will be one file per PRSTDataWriter/PRSTDataReader pair.

The directory must exist; otherwise the service will report an error upon start up.

Default: current working directory

<file_prefix>

A name prefix associated with all the files created by Persistence Service.

Default: PS

<journal_mode>

Sets the journal mode of the persistent storage. This tag can take these values:

• DELETE: Deletes the rollback journal at the conclusion of each transaction.
• TRUNCATE: Commits transactions by truncating the rollback journal to zero-length instead of deleting it.
• PERSIST: Prevents the rollback journal from being deleted at the end of each transaction. Instead, the header of the journal is overwritten with zeros.
• MEMORY: Stores the rollback journal in volatile RAM. This saves disk I/O.
• WAL: Uses a write-ahead log instead of a rollback journal to implement transactions.
• OFF: Completely disables the rollback journal. If the application crashes in the middle of a transaction when the OFF journaling mode is set, the files containing the DDS samples will very likely be corrupted.

Default: WAL

<synchronization>

Determines the level of synchronization with the physical disk.

This tag can take three values:

• FULL: Every DDS sample is written to physical disk as Persistence Service receives it.
• NORMAL: DDS samples are written to disk at critical moments.
• OFF: No synchronization is enforced. Data will be written to physical disk when the OS flushes its buffers.

Default: NORMAL

<trace_file>

Specifies the name of the trace file for debugging purposes. The trace file contains information about all SQL statements executed by the persistence service.

Default: No trace file is generated