Rewrite README

README.md

@@ -1,23 +1,25 @@
 CavalliumDB Engine
 ==================
 
-A very simple wrapper for RocksDB and Lucene, with gRPC and direct connections.
+A very simple reactive wrapper for RocksDB and Lucene.
 
 This is not a database, but only a wrapper for Lucene Core and RocksDB, with a bit of abstraction.
 
 # Features
-## RocksDB Key-Value NoSQL database engine
+- **RocksDB key-value database engine**
   - Snapshots
-- Multi-column databases
-- WAL and corruption recovery strategies
+  - Multi-column database
+  - Write-ahead log and corruption recovery
   - Multiple data types:
-  - Bytes (Singleton)
-  - Maps of bytes (Dictionary)
-  - Maps of maps of bytes (Deep dictionary)
-  - Sets of bytes (Dictionary without values)
-  - Maps of sets of bytes (Deep dictionary without values)
+    - Single value (Singleton)
+    - Map (Dictionary)
+    - Composable nested map (Deep dictionary)
+  - Customizable data serializers
+  - Values codecs
+  - Update-on-write value versioning using versioned codecs
   
-## Apache Lucene Core indexing library
+- **Apache Lucene Core indexing library**
+  - Snapshots
   - Documents structure
   - Sorting
     - Ascending and descending
@@ -34,22 +36,33 @@ This is not a database, but only a wrapper for Lucene Core and RocksDB, with a b
     - Stemming
     - Stopwords removal
   - Results filtering
-- Snapshots
 
 # F.A.Q.
-## Why is it so difficult?
-This is not a DMBS.
+- **Why is it so difficult to use?**
   
-This is an engine on which a DBMS can be built upon. For this reason it's very difficult to use it directly without using it through abstraction layers.
+  This is not a DBMS.
   
-## Can I use objects in the database?
-Yes you must serialize/deserialize them using a library of your choice.
+  This is an engine on which a DBMS can be built upon; for this reason it's very difficult to use directly without building another abstraction layer on top.
   
-## Why there is a snapshot function for each database part?
-Since RocksDB and lucene indices are different instances, every instance has its own snapshot function.
+- **Can I use objects instead of byte arrays?**
   
-To have a single snapshot you must implement it as a collection of sub-snapshots in your DBMS.
+  Yes, you must serialize/deserialize them using a library of your choice.
+  
+  CodecSerializer allows you to implement versioned data using a codec for each data version.
+  Note that it uses 1 to 4 bytes more for each value to store the version.
+  
+- **Why there is a snapshot function for each database part?**
+  
+  Since RocksDB and lucene indices are different software, you can't take a snapshot of everything in the same instant.
+  
+  A single snapshot must be implemented as a collection of all the snapshots.
+  
+- **Is CavalliumDB Engine suitable for your project?**
   
-## Is CavalliumDB Engine suitable for your project?
   No.
-This engine is largely undocumented, and it doesn't provide extensive tests on its methods.
+  
+  This engine is largely undocumented, and it doesn't provide extensive tests.
+
+# Examples
+
+In `src/example/java` you can find some quick implementations of each core feature.

src/main/java/it/cavallium/dbengine/lucene/searcher/ParallelCollectorStreamSearcher.java

@@ -48,13 +48,13 @@ public class ParallelCollectorStreamSearcher implements LuceneStreamSearcher {
 						if (!realFields.isEmpty()) {
 							logger.error("Present fields:");
 							for (IndexableField field : realFields) {
-								logger.error(" - " + field.name());
+								logger.error(" - {}", field.name());
 							}
 						}
 					} else {
 						var field = d.getField(keyFieldName);
 						if (field == null) {
-							logger.error("Can't get key of document docId:" + docId);
+							logger.error("Can't get key of document docId: {}", docId);
 						} else {
 							resultsConsumer.accept(new LLKeyScore(field.stringValue(), score));
 						}

src/main/java/it/cavallium/dbengine/lucene/searcher/SimpleStreamSearcher.java

@@ -41,9 +41,9 @@ public class SimpleStreamSearcher implements LuceneStreamSearcher {
 				logger.error("The document docId: {}, score: {} is empty.", docId, score);
 				var realFields = indexSearcher.doc(docId).getFields();
 				if (!realFields.isEmpty()) {
-					System.err.println("Present fields:");
+					logger.error("Present fields:");
 					for (IndexableField field : realFields) {
-						System.err.println(" - " + field.name());
+						logger.error(" - {}", field.name());
 					}
 				}
 			} else {