Code completion, find references and go to definition not working on large org

Summary

When using VS Code with Salesforce plugin on a large org, the code completion, find references and go to definition is not working. The test panel is also empty.

Steps To Reproduce:

1. Create a project and get source code from a large org.
2. Right click on a method and select Find all references or Go to Definition.

Expected result

The reference panel should show corresponding references or the editor should open the definition.

Actual result

The panel remains empty and the Apex Language Server console is displaying the following error :

GRAVE: Internal error: java.lang.reflect.InvocationTargetException
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:67)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.request(GenericEndpoint.java:120)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleRequest(RemoteEndpoint.java:261)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:190)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:192)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:94)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:99)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:65)
	... 11 more
Caused by: java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Unknown Source)
	at sun.misc.IOUtils.readFully(Unknown Source)
	at java.util.jar.JarFile.getBytes(Unknown Source)
	at java.util.jar.JarFile.getManifestFromReference(Unknown Source)
	at java.util.jar.JarFile.getManifest(Unknown Source)
	at sun.misc.URLClassPath$JarLoader$2.getManifest(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.access$100(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at org.eclipse.jdt.internal.core.nd.field.FieldSearchIndex.asList(FieldSearchIndex.java:300)
	at apex.jorje.lsp.impl.index.ApexIndex.getTestMethods(ApexIndex.java:247)
	at apex.jorje.lsp.impl.tests.StandardTestService.getTestMethods(StandardTestService.java:58)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:65)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint$$Lambda$129/13276447.apply(Unknown Source)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.request(GenericEndpoint.java:120)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleRequest(RemoteEndpoint.java:261)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:190)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:192)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:94)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:99)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)

Additional information

The issue seems related to #1103 and #1101. I get this issue since 3 days only with large org (500 classes, 50 triggers, 180 pages, 380 tests) but not with SFDX small projects.

VS Code Version: 1.33.1

SFDX CLI Version: 45.12.1

OS and version: Windows 10 Enterprise Version 10.0.15063

[praksb]

@TwistyPop I am a Salesforce employee and work on the Apex extension. We are aware of the perf issue and has been incrementally rolling out fixes that would improve the experience for customers with huge number of Apex classes and triggers. #1430 is one such fix that would reduce the memory usage. We have work in our backlog to continue to make such improvements in the near future.

[ClemABT]

@TwistyPop the setting I changed is salesforcedx-vscode-apex.java.home I set it up to point to a 64-bits JRE located in C:\Program Files\Java\jre1.8.0_231