SummaryOn the Exinda appliance, the database backend that is used is MySQL. There are some occasions whe nit cannot start due to a lack of RAM available on the system as necessary to run optimally.
OverviewWhile collecting all the data, the Exinda appliance needs to store the information somewhere. It is done through saving the information to a MySQL instance, in multiple databases, depending on what the information is and where it needs to go. MySQL, as the provider of the database system, needs as much RAM as is required for the number of accesses (both reading and writing). If MySQL does not get this RAM, it will exit the application and cause reporting to go down along with it, including the graphs on the web UI and PDF reporting functionality.
The MySQL daemon (mysqld) in the system requires a fair amount of RAM. While there is no defined amount of RAM that it can and should use - as this depends on not only hardware, but also on traffic patterns as well as how often reporting is accessed, etc - it will use a portion. When mysqld fails, in the logs it will note that it has done so. There might be a diagnostic generated as well under System > Diagnostics, on the "Diagnostics" tab. There are no checks for MySQL starting up after a crash if the amount of memory is too low. If, for some reason, other processes are taking up an excess of 90% of the memory on the system, it might not be possible for mysqld to restart, or it might try and crash again.
As a safe estimate, ensuring that there is 10% free memory to run MySQL is a good practice, though depending on the environment, it might need more or less. At the low end, on a low traffic system, mysqld can use 400MB of Memory. It can use upwards of 5GB on high traffic systems.