Log-based or trigger-based database capture?

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  • #8879
    Mark
    Keymaster

    Why would I still use trigger-based database capture when HVR supports log-based capture on all platforms?

    The general rule is to use log-based capture, unless you have a good reason not to.

    Log-based capture is beneficial over trigger-based capture because:

    • Log reading takes place asynchronously, so transaction processing is not directly affected by log-based change data capture.
    • The transaction log has a history of changes, so it is possible to go back in time and re-capture changes should that be necessary.
    • Generally log-based capture uses less system resources than trigger-based capture, and does this more in a continuous mode rather than in bursts.

    However there are uncommon exceptions when trigger-based capture may be used as an alternative.

    • The database you want to capture from does not provide sufficient required functionality for HVR to perform log-based capture. A good example is SQL Server Express Edition which does not allow HVR to add supplemental logging to tables and hence log-based capture cannot be used.
    • The database does not provide required access to the logs. This may be the case in some cloud environments like Azure SQL.
    • The database runs on an old and unsupported OS but is still in use. For example there are still Ingres databases out there running on VMS…
    • Additional logic is required upon capture, e.g. to support capture out of views as documented in the User Manual.

    Please note that HVR does not support trigger-based capture on all supported source platforms. It is supported on Oracle, SQL Server and Ingres.

    #11085
    ggoodrich
    Keymaster

    Hi Nameet, and thank you for the question about HVR support for Oracle on ‘Amazon RDS’ as a source. HVR 5.2 supports sourcing from Oracle RDS using our trigger-based solution only. This is currently due to the condition mentioned in the second bullet listed above: database does not provide required access to the logs. The HVR engineering team is currently working on a new log-based method which will be announced in a future release.

    #12937
    Anonymous
    Inactive

    Is there a resource that points at how to configure the trigger-based solution with RDS? Is RDS PostgreSQL supported?

    #12939
    ggoodrich
    Keymaster

    Hello CA, starting in HVR 5.3.0, we now support log-based capture from PostgreSQL RDS using a SQL interface.  At a high level, the machine running HVR must install the client software to connect to the database (i.e. PostgreSQL client). Then in HVR the “Location Configuration” i.e. the connection to the database is defined differently. Action Capture would use /LogReadMethod=SQL, and everything else is the same.

    Note for PostgreSQL we must have the decoding plugin installed (this is available in the open source community).

    Details are included in our installation instructions:

    – PostgreSQL: https://www.hvr-software.com/wiki/Requirements_for_PostgreSQL

    Best,

    GG

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