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Eliminate the impact of temporary access loss to the VBD cluster (8.4)

Improvements to the reliability of Visual Business Director (VBD) include the ability to continue writing data to a VBD dataset while the corresponding server node is unavailable, enhancements to single-case data flows that write data to VBD, and a reduction in the VBD cache size.

Starting in version 8.4 of Pega Platform™, VBD uses Stream API to asynchronously write data to the VBD server. Each VBD server node listens to the stream and reads the records from the stream in batches. If a node is temporarily unavailable, the writing can now continue, improving the stability of the process.

Reading data from the VBD server is still synchronous, so if a node is temporarily unavailable, reading operations pause until the node is back online.

After a previously unavailable node is back online, you can now check the new Consumer lag diagnostic on the Real-time Data Grid page for information about the node status. The diagnostic displays the number of records that have not yet been read from the VBD stream. If nodes are working without incident, the diagnostic shows no records, as in the following figure:

Consumer lag diagnostic during normal operations
"Consumer lag diagnostic during normal operations"
Consumer lag diagnostic during normal operations

If a node is or was recently unavailable, the diagnostic shows the number of records that remain to be processed. After the node is back online, the number should automatically decrease over time, as VBD data is read from the stream.

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