Add comments relating memory sizing.

charts/stardog/README.md

@@ -57,6 +57,28 @@ Configuration Parameters
 
 The default values are specified in `values.yaml` as well as the required values for the ZooKeeper chart.
 
+Memory Parameters
+-----------------
+
+Memory settings are part of both javaArgs and resources within
+values.yaml.  The settings must be coordinated.
+
+Stardog will aggressive use all memory allocated to it via the
+javaArgs settings of -Xmx and -XX:MaxDirectMemorySize.  The total
+memory used by Stardog is the sum of -Xmx and -XX:MaxDirectMemorySize.
+
+The resources settings of requests:memory and optional limits:memory
+must account for the javaArgs settings.  requests:memory should be at
+least 1g larger than -Xms and -XX:MaxDirectMemorySize total. 2g larger is
+preferred.  If you chose to establish resourse:limits, limits:memory
+must be at least 1g larger than -Xmx and -XX:MaxDirectMemorySize total.  A
+too small limits:memory setting will likely result in a system crash.
+
+Network based disk storage is not recommended.  If used, the
+limits:memory should be at least 4g larger than -Xmx and
+-XX:MaxDirectMemorySize total.  Network storage often caches large
+writes related to data loads and db optimizations.
+
 Upgrades
 --------
 

charts/stardog/values.yaml

@@ -24,6 +24,8 @@ cluster:
 terminationGracePeriodSeconds: 300
 
 # Java args for Stardog server
+#  Shown are memory sizing parameters.  Total potential memory is sum of
+#  -Xmx and -XX:MaxDirectMemorySize.  In this sample, the total memory is 3g
 javaArgs: "-Xmx2g -Xms2g -XX:MaxDirectMemorySize=1g"
 
 # Additional arguments passed to Stardog at server start
@@ -81,6 +83,8 @@ antiAffinity: requiredDuringSchedulingIgnoredDuringExecution
 
 # Stardog should have at least 2 CPUs. The CPU request value is used to set
 # -XX:ActiveProcessorCount=N for the JVM.
+# If limits:memory is activated, it must be at least 1g larger than the
+#   total of javaArg's -Xmx and -XX:MaxDirectMemorySize.  2g larger is recommended.
 resources:
   requests:
     cpu: 2