Extract Trail and Files Overview
- Extract writes data to any of the following:
- Local trail (ExtTrail) on the local system (Limited to two character prefix and sequence number)
- Local file (ExtFile) on the local system
- Remote trail (RmtTrail) on a remote system
- Remote file (RmtFile) on a remote system
- Extract trails and files are unstructured, with variable length records.
– I/O is performed using large block writes.
- Extract writes checkpoints for trails during change capture.
– This guarantees that no data is lost during restart.
– Multiple Replicat processes may process the same trail.
Extract does not write checkpoints for files.
Extract Trail and Files: Distribution
- Extract can write to:
Local trails, and then distribute over IP with a data pump to remote trails
Multiple trails for distribution to multiple systems/disk storage devices and for parallel processing by downstream processes.
Trails and files can be transported online using TCP/IP or sent in a batch using any file transfer method.
Extract Trails and Files: Contents
- Each record in the trail contains an operation that has been committed in the source database.
- The committed transactional order is preserved.
- Operations in a transaction are grouped together in the order in which they were applied.
- By default, only the primary key and changed columns are recorded.
- Flags indicate the first and last records in each transaction.
- Starting from Oracle GoldenGate release 12.2, the trail files also contain metadata information about database objects being replicated.
Extract Trails and Files: Cleanup
- Trail files can be purged after they are consumed.
- The temporary storage requirement is small if processes keep pace.
- Configure the MA Administration Server with the Purge Trails task.
- Configure the CA Manager to purge used trail data (best practice).
Setting the Compatibility Level
- The <major>.<minor> setting identifies the trail file format version numbers used by Oracle GoldenGate.
- This allows customers to use different versions of Oracle GoldenGate Extract, trail files, and Replicat together.
- The compatibility level is set in the Extract ExtFile, ExtTrail, RmtFile or RmtTrail parameter: RmtTrail ./dirdat/ex, Format Release 12.3
- The data pump Extract writes the output trail in the same format and the metadata endian as the input source trail file.
It is recommended that all instances of Oracle GoldenGate be the same version to take advantage of the new functionality. However, this is not required.