For anyone that gets OOME (out of memory errors) with the java heap space, then this is how I solved it to allow me to drop the refresh down to 1000ms. I have had my two cameras running for >24 hours without issues. I suspect this has to do with javas garbage collection not running often enough to deal with the large amounts of data passing through the image item if you are running your system close to the max allocated heap size.
In the openhab console run this command (optional just for your info)
shell:info
It gives you output like this…
Karaf
Karaf version 4.1.5
Karaf home /usr/share/openhab2/runtime
Karaf base /var/lib/openhab2
OSGi Framework org.eclipse.osgi-3.12.50.v20170928-1321
JVM
Java Virtual Machine OpenJDK Client VM version 25.152-b76
Version 1.8.0_152
Vendor Azul Systems, Inc.
Pid 418
Uptime 13 hours 15 minutes
Total compile time 12 minutes
Threads
Live threads 175
Daemon threads 71
Peak 199
Total started 6482
Memory
Current heap size 183,100 kbytes
Maximum heap size 243,520 kbytes
Committed heap size 238,552 kbytes
Pending objects 0
Garbage collector Name = 'Copy', Collections = 8778, Time = 4 minutes
Garbage collector Name = 'MarkSweepCompact', Collections = 437, Time = 7 minutes
Classes
Current classes loaded 20,333
Total classes loaded 20,509
Total classes unloaded 176
Operating system
Name Linux version 4.14.52-v7+
Architecture arm
Processors 4
Run this in linux to open the file for editing after typing in logout to exit the console. (required: this is changing the heap size)
sudo nano /etc/default/openhab2
Change the already existing line to have this if it is empty. The -Xmx512m gives the heaps more space to grow up to a max of 512mb. (required: this is changing the heap size)
EXTRA_JAVA_OPTS="-XX:+HeapDumpOnOutOfMemoryError -Xmx512m"
Save and exit using the commands listed at the bottom of the screen, then…
sudo reboot
Lastly you can check the ram usage with this command… (optional)
free -h
example output after doing the above and a reboot on a pi2 is
total used free shared buff/cache available
Mem: 976M 373M 374M 9.7M 228M 545M
Swap: 99M 0B 99M