[GitHub] [pulsar] merlimat commented on a diff in pull request #17948: [improve][java-client][issue-17931]Reduce call of hashFunction in SchemaHash

[GitBox <gi...@apache.org>]

merlimat commented on code in PR #17948:
URL: https://github.com/apache/pulsar/pull/17948#discussion_r990636497


##########
pulsar-common/src/main/java/org/apache/pulsar/common/protocol/schema/SchemaHash.java:
##########
@@ -55,15 +82,123 @@ public static SchemaHash of(SchemaData schemaData) {
     }
 
     public static SchemaHash of(SchemaInfo schemaInfo) {
-        return of(schemaInfo == null ? new byte[0] : schemaInfo.getSchema(),
+        return of(schemaInfo == null ? null : schemaInfo.getSchema(),
                 schemaInfo == null ? null : schemaInfo.getType());
     }
 
-    public static SchemaHash of(byte[] schemaBytes, SchemaType schemaType) {
-        return new SchemaHash(hashFunction.hashBytes(schemaBytes), schemaType);
+    public static SchemaHash empty() {
+        return of(null, null);
+    }
+
+    private static SchemaHash of(byte[] schemaBytes, SchemaType schemaType) {
+        SchemaHash result;
+        if (schemaBytes == null || schemaBytes.length == 0) {
+            result = EmptySchemaHashFactory.get(schemaType);
+            if (result == null) {

Review Comment:
   Why should that method possibly fail? Couldn’t we assume that it always returns a result. This would simplify the code here. 



##########
pulsar-common/src/main/java/org/apache/pulsar/common/protocol/schema/SchemaHash.java:
##########
@@ -55,15 +82,123 @@ public static SchemaHash of(SchemaData schemaData) {
     }
 
     public static SchemaHash of(SchemaInfo schemaInfo) {
-        return of(schemaInfo == null ? new byte[0] : schemaInfo.getSchema(),
+        return of(schemaInfo == null ? null : schemaInfo.getSchema(),
                 schemaInfo == null ? null : schemaInfo.getType());
     }
 
-    public static SchemaHash of(byte[] schemaBytes, SchemaType schemaType) {
-        return new SchemaHash(hashFunction.hashBytes(schemaBytes), schemaType);
+    public static SchemaHash empty() {
+        return of(null, null);
+    }
+
+    private static SchemaHash of(byte[] schemaBytes, SchemaType schemaType) {
+        SchemaHash result;
+        if (schemaBytes == null || schemaBytes.length == 0) {
+            result = EmptySchemaHashFactory.get(schemaType);
+            if (result == null) {
+                log.warn("Could not get schemaHash from EmptySchemaHashFactory, will create by hashFunction. Might"
+                                + " bring performance regression. schemaBytes:{}, schemaType:{}",
+                        schemaBytes == null ? "null" : "0", schemaType);
+                result = new SchemaHash(
+                        hashFunction.hashBytes(schemaBytes == null ? new byte[0] : schemaBytes), schemaType);
+            }
+        } else {
+            result = new SchemaHash(hashFunction.hashBytes(schemaBytes), schemaType);
+        }
+        return result;
     }
 
     public byte[] asBytes() {
         return hash.asBytes();
     }
+
+    private static class EmptySchemaHashFactory {

Review Comment:
   It may require some refactoring though why not having SchemaInfo.hash() method? The schemas are already all statically initialized 



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