SAI-5261: fix CaffeineCache.put ramBytes decrement (#240)

(cherry picked from commit caff168)

solr/core/src/java/org/apache/solr/search/CaffeineCache.java

@@ -275,7 +275,15 @@ public V computeIfAbsent(K key, IOFunction<? super K, ? extends V> mappingFuncti
   public V put(K key, V val) {
     inserts.increment();
     V old = cache.asMap().put(key, val);
-    recordRamBytes(key, old, val);
+    // ramBytes decrement for `old` happens via #onRemoval
+    if (val != old) {
+      // NOTE: this is conditional on `val != old` in order to work around a
+      //  behavior in the Caffeine library: where there is reference equality
+      //  between `val` and `old`, caffeine does _not_ invoke RemovalListener,
+      //  so the entry is not decremented for the replaced value (hence we
+      //  don't need to increment ram bytes for the entry either).
+      recordRamBytes(key, null, val);
+    }
     return old;
   }
 

solr/core/src/test/org/apache/solr/search/TestCaffeineCache.java

@@ -308,7 +308,7 @@ public void testRamBytesSync() throws IOException {
 
     cache.put(0, "test");
     long nonEmptySize = cache.ramBytesUsed();
-    cache.put(0, "test");
+    cache.put(0, random().nextBoolean() ? "test" : "rest");
     assertEquals(nonEmptySize, cache.ramBytesUsed());
 
     cache.remove(0);
@@ -341,7 +341,7 @@ public void testRamBytesAsync() throws IOException {
 
     cache.put(0, "test");
     long nonEmptySize = cache.ramBytesUsed();
-    cache.put(0, "test");
+    cache.put(0, random().nextBoolean() ? "test" : "rest");
     assertEquals(nonEmptySize, cache.ramBytesUsed());
 
     cache.remove(0);