In case all Cassandra nodes associated with a DMA are down, database files will be offloaded to the system cache folder on disk, and will be pushed to the database once the connection becomes available again.
I wonder if there is a way to manually enable the offload while the database is up and running?
For debugging purposes, I’d like to see what exactly is being pushed to the database in terms of trend data, element data, etc…, without having to temporarily disconnect the database.
Hello Ruben,
There is the message “FileOffloadToggleRequest”, which does exactly what you need (can be sent through the SLNetClientTest tool).
However, this might not work on some versions (in the 9.6.x range). We’ve also reworked offload since RN25917, which should be in 10.0.9. This message should only be used for debugging purposes though.
Unlike MySQL, its good to note that the data is being serialized into files that can’t be read without deserializing (when on fileoffload).
Hi Ruben,
Not really what you asked for, but you can enable tracing on Cassandra to track history queries.
More details can be found here.
Do keep in mind that this should only be enabled temporarily, as it has a major impact on the system performance.
Thanks Ive. Very useful and in the end pretty much what we’re after. We’ll look into that.
After further testing, it looks like enabling tracing will only trace queries made through the cqlsh prompt and DevCenter, not queries made by DataMiner.
it’s indeed not possible to see which queries are running on a Cassandra database. There is however logging in SLDataGateway in case a queue starts to build up towards a certain table.
Next to that we are currently looking into creating a BPA that will be able to provide you this information
Thanks Marlies. It was actually a line in the SLDataGateway log file related to a build-up of element data changes that triggered us to check if there is an easy way to see what is pushed to db during a given time span.
Thanks Thomas. Although it looks like sending the ‘FileOffloadToggleRequest’ manually seems to be broken in 10.0.9, I believe once working it’s currently the best approach for getting insight into data sent to the db.
Note: The sqlite offload file needs to be deserialized in order to extract any useful data.