fetchRingBufferSize should be global to all the created RingBufferThread in a JVM

[odelpozog]

Hello

Some Denodo Technologies customers are facing java.lang.OutOfMemoryError issues executing Redshift queries in a concurrent way with the Reshift 2.x JDBC drivers. By default, the enableFetchRingBuffer feature is enabled and multiple instances of RingBufferThread are created with 1GB of max size when multiple queries are executed.

When this happens, as the buffers are filling up, the heap memory grows and, eventually, a java.lang.OutOfMemoryError is raised:

I think that the fetchRingBufferSize should limit the total JVM memory used by all the RingBufferThread instances, not the size of each RingBufferThread instance. Otherwise, JDBC clients with concurrent queries should not enable the RingBuffer feature to avoid possible OOM issues.