The Extract process sequentially writes committed transactions as they occur to a staging file that
GoldenGate calls a source trail. Data is written in large blocks for high performance. Data that is written
to the trail is queued for distribution to the target server or another destination to be processed by
another GoldenGate process, such as a data pump. Data in the trail files can also be encrypted by the
Extract and then unencrypted by the data pump or delivery process.
You can size the trail files based on the expected data volume. When the specified size is reached, a
new trail file is created. To free up disk space, you can configure GoldenGate to automatically purge trail
files based on age or the total number of trail files.
By default, data in the trail files is stored in a platform-independent, GoldenGate proprietary format.
In addition to the database data, each trail file contains a file header, and each record also contains its
own header. Each of the GoldenGate processes keeps track of its position in the trail files using
checkpoints, which are stored in separate files.

因此同一个复制进程之内，ogg同步是串行的