Direct Memory Allocations Tracing
OrientDB uses off-heap memory pool for its file cache allocations. Direct memory allocations tracing allows to trace allocations done by this pool.
Use direct memory allocations tracing for debugging and troubleshooting purposes only, since it significantly slowdowns OrientDB off-heap memory management infrastructure. Never leave the tracer turned on in a production setup.
Activating Allocations Tracing
To activate allocations tracing provide the memory.directMemory.trace=true configuration option to the OrientDB instance in question. For example, you may provide following command line argument to the JVM:
java ... -Dmemory.directMemory.trace=true ...
Alternatively, you may enable/disable the tracer at runtime by changing the value of OGlobalConfiguration#DIRECT_MEMORY_TRACE setting or by invoking startTracing/'stopTracing' operation on the com.orientechnologies.common.directmemory:type=OByteBufferPoolMXBean JMX bean.
Inspecting the Log
After activation of the tracing, information about relevant events will be written to regular OrientDB log. Related log entries are marked with the DIRECT-TRACE label. General format of the log entry looks like:
DIRECT-TRACE $event: $name = $before + $delta = $after, buffer = $buffer_id
$event– the event type.$name– the name of the value being changed.$before– the value before the event.$delta– the delta of the value.$after– the value after the event.$buffer_id– the identifier of the buffer related to the event, if any.
Tracer is able to report following event types:
AcquiredFromPool– the buffer is acquired/reused from the pool; change in the pool size is reported.OverflowBufferAllocated– the overflow buffer allocated; changes in the overflow buffer count and in the total allocated memory are reported. Usually, overflow allocations indicate memory settings misconfiguration and/or low-memory conditions.SlicedFromPreallocatedArea– the buffer is allocated/sliced from a large preallocated chunk of the memory; the change in the chunk size is reported.FallbackBufferAllocated– the fallback overflow buffer allocated; changes in the overflow buffer count and in the total allocated memory are reported. Usually, fallback overflow allocations indicate severe memory settings misconfiguration and/or severe low-memory conditions.AllocatedForPreallocatedArea– the large preallocation buffer is allocated to slice smaller buffers from it later; change in the total allocated memory is reported.ReturnedToPool– the buffer is returned to the pool; change in the pool size is reported.DirectBufferPoolSizeChanged– JVM's allocated direct memory size is changed.
Event Aggregation
You may change the "spamness" of the tracer by adjusting the value of memory.directMemory.trace.aggregation setting. Possible values:
none– for no aggregation, events are traced one-by-one.low– for low aggregation which provides more details.medium(default) – provides medium level of details.high– provides low level of details.
Alternatively, you may adjust the aggregation level at runtime by changing the value of OGlobalConfiguration#DIRECT_MEMORY_TRACE_AGGREGATION setting or by changing the value of the TraceAggregation attribute on the com.orientechnologies.common.directmemory:type=OByteBufferPoolMXBean JMX bean.