4.2. Special Considerations for Existing Customers


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4.2. Special Considerations for Existing Customers

Many of the new features and capabilities in Volt V9.0 do not impact existing applications. However, there are a few changes that may require action for users upgrading from earlier versions. Existing customers should take note of of the following changes:

  • Change to how stream data is queued for export

    Previously, if you defined a stream with the EXPORT TO TARGET clause but no matching target was configured, any data inserted into the stream was dropped. No data was queued until the specified target was both configured and successfully connected. With Volt 9.0 export queuing has been simplified: data is queued as soon as the stream is declared and the queue is deleted as soon as the stream is dropped.

    This means that if you declare a stream and it is being written to, but you do not configure the associated target, the data inserted into the stream will be queued in the export_overflow directory, consuming disk space that would not have been used in earlier versions of the product.

  • Change to the reporting of streams in @Statistics

    In Volt 8.4, a new @Statistics selector, EXPORT, was introduced to provide improved visibility and more detail concerning the export lifecycle. At that time, export streams continued to be reported under the TABLE selector, so as not to disrupt existing scripts or procedures users might have that rely on that information. With Volt 9.0, export streams have been removed from the TABLE selector results. Now the TABLE selector only reports on tables and streams that are not associated with an export target. Information on streams declared with the EXPORT TO TARGET clause is provided under the EXPORT selector.

  • Managing export queues during outages

    In most cases, Volt manages the export queues even in unusual cases where nodes go down in a K-safe cluster. If at any time the node managing an export partition finds a gap in the export queue (due to the current server having been down when that data was written to the stream), the system queries the other servers to find one with the missing data and export continues. In the rare case where Volt cannot find the missing records in any of the current server export queues, the export connector for that queue will stop, waiting for a server that has the data.

    Even if servers stop and rejoin frequently, the data will eventually be found on a rejoining node. However, in the unusual case that, say, failed nodes are replaced by new, initialized servers, it is possible that the gap in the queue cannot be resolved. Previously, Volt would eventually (once the cluster was at a full complement of servers) skip the missing data and restart the connector at the next available export record. Starting with Volt 9.0, export will not skip over gaps automatically. The queue will stop and warnings will be logged to the console and reported via SNMP. You must issue the voltadmin export release command to resume processing of the export connector at the next available record.

  • Limits on streams in Community Edition

    Export is now an Enterprise Edition feature and the Community Edition is limited to two streams per database. This means if you try to restore a database from a previous version with more than two streams using the Volt 9.0 Community Edition, the restore will fail. If this happens when upgrading, you can initialize a new database root, load the schema without the additional streams, then manually restore the data.

  • Support for CentOS and RHEL 6 removed

    The officially supported platforms for Volt have been updated. CentOS and RHEL version 6 are no longer officially supported. The current list of supported platforms include CentOS and RHEL version 7.0 or later, Ubuntu versions 14.04, 16.04, and18.04, and Macintosh OS X 10.9 or later.

  • Support for export and import to Kafka 0.8.2 removed

    The Kafka import and export connectors now require Kafka version 0.10.2 or later.

  • Logging name change from JOIN to ELASTIC

    The log4J logger reporting on elastic changes to Volt clusters has been renamed from JOIN to ELASTIC.