Architecture of Extract Trails and Files

Oracle Golden Gate trail supports continuous extraction and replication of database changes and stores them temporarily on disk.

Extract process can write to the following type of files :

1. The extract can write to trail file on local disk, we know it as exttrail.

2. The extract can write to trail file on remote server disk, we know it as rmttrail.

3. The extract can write to the local file on disk, known as extfile.

4. The extract can write to a remote file on remote disk, known as rmtfile.

Trail and files generated by the extract process are unstructured and are of variable length. I/O performed on this file is performed using large block writes.

Extract process writes checkpoints for trail during change capture, which ensures that no data is lost during restart. Multiple replicat processes may use the same trail file.

Note: Extract does not write checkpoint for files.

Contents of Trail or Files :

1. Each record on trail or files contains committed transaction of the source database.

2. Order of committed transaction is preserved.

3. Only primary key and columns those are changed are stored in trail and files in case of an update.

The format for Trail Files :

Trail files are written in canonical format. Allowing them to be exchanged precisely and quickly among divergent databases.

Each trail file contains the following :

Record Header Area

Record Data Area

Each trail’s record header area contains the following information :

1. Trail File Information: Which contains compatibility level, the creation time of trail file, the character set of, size of file and sequence no of the file.
2. First and Last record information of timestamp and Commit sequence number.
3. Extract information: Golden Gate version of extract, the name of extract group, hostname and hardware type etc.

Each trail file’s Data Area contains the following information :

1. Trail record header.
2. The time that the change was written to the golden gate trail file.
3. Insert ,update or delete [type of database operation].
4. Length of the record.
5. Table name, rba withing trail file etc.

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