Too many duplicated Name.Literal instances

[JaroslavTulach]

I've executed Enso program as enso --run test/Base_Tests and in the middle of execution I have taken a heap dump. Then I used VisualVM to compute histogram of Name.Literal instances based on their name. There is a lot of duplicates - for example Standard is repeated 15000 times!

The program to execute in OQL console is:

var histo = {};
heap.forEachObject(function(l) {
  var n = l.name.toString();
  var cnt = histo[n];
  if (!cnt) {
    histo[n] = 1;
  } else {
    histo[n] = cnt+1;
  }
}, 'org.enso.compiler.core.ir.Name$Literal')

var arr = []
for (var n in histo) {
  arr.push([n, histo[n]])
}
arr.sort(function(p1, p2) { return p2[1] - p1[1]; })
arr

[JaroslavTulach]

The generated code for persistance of Name.Literal is using writeUTF to store the String name:

@Override
  protected void writeObject(org.enso.compiler.core.ir.Name.Literal obj, Output out) throws IOException {
    out.writeUTF(obj.name());
    out.writeBoolean(obj.isMethod());
    out.writeInline(scala.Option.class, obj.location());
    out.writeInline(scala.Option.class, obj.originalName());
    out.writeInline(org.enso.compiler.core.ir.MetadataStorage.class, obj.passData());
    out.writeInline(org.enso.compiler.core.ir.DiagnosticStorage.class, obj.diagnostics());
  }

the writeUTF method currently stores the name "in place" - e.g. repeats the characters again and again. If we replace that line with:

      out.writeObject(obj.name().intern());

the size of the Standard.Base .bindings cache goes down from 42MB to 32MB and overall we save 23% on the size of all caches.

[JaroslavTulach]

One other method is to use writeObject and readObject for String in the generated classes:

$ git diff 
diff --git lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
index e7ee6e05f4..ab17b3685f 100644
--- lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
+++ lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
@@ -182,7 +182,9 @@ public class PersistableProcessor extends AbstractProcessor {
       if (cons != null) {
         for (var v : cons.getParameters()) {
           if (tu.isSameType(eu.getTypeElement("java.lang.String").asType(), v.asType())) {
-            w.append("    var ").append(v.getSimpleName()).append(" = in.readUTF();\n");
+            w.append("    var ")
+                .append(v.getSimpleName())
+                .append(" = (java.lang.String) in.readObject();\n");
           } else if (!v.asType().getKind().isPrimitive()) {
             var type = tu.erasure(v.asType());
             var elem = (TypeElement) tu.asElement(type);
@@ -241,7 +243,7 @@ public class PersistableProcessor extends AbstractProcessor {
       if (cons != null) {
         for (var v : cons.getParameters()) {
           if (tu.isSameType(eu.getTypeElement("java.lang.String").asType(), v.asType())) {
-            w.append("    out.writeUTF(obj.").append(v.getSimpleName()).append("());\n");
+            w.append("    out.writeObject(obj.").append(v.getSimpleName()).append("());\n");
           } else if (!v.asType().getKind().isPrimitive()) {
             var type = tu.erasure(v.asType());
:...skipping...
diff --git lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
index e7ee6e05f4..ab17b3685f 100644
--- lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
+++ lib/java/persistance-dsl/src/main/java/org/enso/persist/impl/PersistableProcessor.java
@@ -182,7 +182,9 @@ public class PersistableProcessor extends AbstractProcessor {
       if (cons != null) {
         for (var v : cons.getParameters()) {
           if (tu.isSameType(eu.getTypeElement("java.lang.String").asType(), v.asType())) {
-            w.append("    var ").append(v.getSimpleName()).append(" = in.readUTF();\n");
+            w.append("    var ")
+                .append(v.getSimpleName())
+                .append(" = (java.lang.String) in.readObject();\n");
           } else if (!v.asType().getKind().isPrimitive()) {
             var type = tu.erasure(v.asType());
             var elem = (TypeElement) tu.asElement(type);
@@ -241,7 +243,7 @@ public class PersistableProcessor extends AbstractProcessor {
       if (cons != null) {
         for (var v : cons.getParameters()) {
           if (tu.isSameType(eu.getTypeElement("java.lang.String").asType(), v.asType())) {
-            w.append("    out.writeUTF(obj.").append(v.getSimpleName()).append("());\n");
+            w.append("    out.writeObject(obj.").append(v.getSimpleName()).append("());\n");
           } else if (!v.asType().getKind().isPrimitive()) {
             var type = tu.erasure(v.asType());
             var elem = (TypeElement) tu.asElement(type);
diff --git lib/java/persistance/src/main/java/org/enso/persist/PerGenerator.java lib/java/persistance/src/main/java/org/enso/persist/PerGenerator.java
index d8a3e2c2bd..d64d7d5d12 100644
--- lib/java/persistance/src/main/java/org/enso/persist/PerGenerator.java
+++ lib/java/persistance/src/main/java/org/enso/persist/PerGenerator.java
@@ -13,7 +13,7 @@ import java.util.function.Function;
 import org.slf4j.Logger;
 
 final class PerGenerator {
-  static final byte[] HEADER = new byte[] {0x0a, 0x0d, 0x13, 0x0f};
+  static final byte[] HEADER = new byte[] {0x0a, 0x0d, 0x13, 0x13};
   private final OutputStream main;
   private final Map<Object, WriteResult> knownObjects = new IdentityHashMap<>();
   private int countReferences = 1;
diff --git lib/java/persistance/src/main/java/org/enso/persist/PerInputImpl.java lib/java/persistance/src/main/java/org/enso/persist/PerInputImpl.java
index 5bfe457cd2..1f6c9c126a 100644
--- lib/java/persistance/src/main/java/org/enso/persist/PerInputImpl.java
+++ lib/java/persistance/src/main/java/org/enso/persist/PerInputImpl.java
@@ -319,11 +319,11 @@ final class PerInputImpl implements Input {
     }
 
     final Object resolveObject(Object res) {
-      if (readResolve != null) {
-        return readResolve.apply(res);
-      } else {
-        return res;
+      var v = (readResolve != null) ? readResolve.apply(res) : res;
+      if (v instanceof String s) {
+        v = s.intern();
       }
+      return v;
     }
 
     final Object getObjectAt(int at) {

with this change the caches are also down to the previous values. Moreover it is guaranteed that various Name.Literal instances point to the same string. By executing following OQL query:

var arr = []
heap.forEachObject(function(l) {
  var n = l.name.toString();
  if (!n.contains("Standard")) {
    return;
  }
  arr.push(l.name)
}, 'org.enso.compiler.core.ir.Name$Literal')

arr

that all the IR.Name.name values are pointing to the identical instance of the string.