fix: NPE when compression algorithm is not set

- improve KANZI compression settings
- update documentation

Author: manticore-projects

h2/src/docsrc/html/advanced.html

@@ -1073,7 +1073,7 @@ <h3 id="direct_one_phase_recover_tool">Direct Recover</h3>
 java -Xmx8g -cp "h2-2.3.239-SNAPSHOT.jar" org.h2.tools.DirectRecover -dir ~/ -db testdb -compress gzip
 
 # resulting SQL script files on a AMD Zen3 Ryzen5:
-# KANZI: testdb.h2.sql.knz (114.1 MB in 128 secs)
+# KANZI: testdb.h2.sql.knz ( 99.7 MB in 106 secs)
 # BZip2: testdb.h2.sql.bz2 (153.7 MB in 18 mins)
 # GZip:  testdb.h2.sql.gz  (207.4 MB in 74 secs)
 </pre>

h2/src/main/org/h2/tools/CompressTool.java

@@ -110,10 +110,15 @@ public static OutputStream createKanziOutputStream(OutputStream baseOutputStream
             // Create configuration map with proper Kanzi parameters
             java.util.Map<String, Object> configMap = new java.util.HashMap<>();
 
-            // Basic compression settings
-            configMap.put("transform", "LZP+BWT");              // Good for text
-            configMap.put("entropy", "CM");                     // Text and structured data
-            configMap.put("blockSize", 128 * 1024 * 1024);      // 128MB blocks
+            //  Best compression settings (brute tested on a 1.7 GB database)
+            //  88658331 kanzi -x64 -b 256m -t RLT+PACK+LZP -e TPAQX
+            //  88654035 kanzi -x64 -b 256m -t RLT+PACK+LZP+RLT -e TPAQX
+            //  85411430 kanzi -x64 -b 256m -t TEXT+RLT+LZP+PACK -e TPAQX
+            //  85397152 kanzi -x64 -b 256m -t TEXT+RLT+LZP+PACK+RLT -e TPAQX
+
+            configMap.put("transform", "TEXT+RLT+LZP+PACK+RLT");// Good for text
+            configMap.put("entropy", "TPAQ");                   // Text and structured data
+            configMap.put("blockSize", 64 * 1024 * 1024);       // 128MB blocks
             configMap.put("level", 9);                          // Max. compression level
             configMap.put("checksum", 64);                      // Enable checksums
 
@@ -153,6 +158,8 @@ public static InputStream createKanziInputStream(InputStream inputStream, Execut
                     InputStream.class,
                     java.util.Map.class
             );
+            // workaround Zero byte EOF issue
+            // it has been fixed only recently so we should still guard for a while
             return new ZeroBytesEOFInputStream( (InputStream) constructor.newInstance(inputStream, configMap));
 
         } catch (ClassNotFoundException e) {

h2/src/main/org/h2/tools/CompressionType.java

@@ -15,6 +15,8 @@ public enum CompressionType {
     LZF;
 
     public static CompressionType from(String type) {
-        return  Enum.valueOf(CompressionType.class, type.toUpperCase(Locale.ENGLISH));
+        return type==null || type.isEmpty()
+            ? NONE
+            : Enum.valueOf(CompressionType.class, type.toUpperCase(Locale.ENGLISH));
     }
 }