LUCENE-8467: RAMDirectory, RAMFile, RAMInputStream, RAMOutputStream are deprecated.

lucene/CHANGES.txt

@@ -147,6 +147,9 @@ Optimizations
 
 API Changes:
 
+* LUCENE-8467: RAMDirectory, RAMFile, RAMInputStream, RAMOutputStream are deprecated
+  (Dawid Weiss)
+
 * LUCENE-8356: StandardFilter is deprecated (Alan Woodward)
 
 * LUCENE-8373: ENGLISH_STOP_WORD_SET on StandardAnalyzer is deprecated.  Instead

lucene/MIGRATE.txt

@@ -99,3 +99,10 @@ IndexSearcher's search and searchAfter methods were changed to only count hits
 accurately up to 1,000, and Topdocs.totalHits was changed from a long to an
 object that says whether the hit count is accurate or a lower bound of the
 actual hit count.
+
+## RAMDirectory, RAMFile, RAMInputStream, RAMOutputStream are deprecated ##
+
+This RAM-based directory implementation is an old piece of code that uses inefficient
+thread synchronization primitives and can be confused as "faster" than the NIO-based
+MMapDirectory. It is deprecated and scheduled for removal in future versions of 
+Lucene. (LUCENE-8467, LUCENE-8438)

lucene/core/src/java/org/apache/lucene/store/RAMDirectory.java

@@ -49,7 +49,12 @@ import org.apache.lucene.util.Accountables;
  * {@link MMapDirectory}, which is a high-performance directory
  * implementation working directly on the file system cache of the
  * operating system, so copying data to Java heap space is not useful.
+ * 
+ * @deprecated This class uses inefficient synchronization and is discouraged
+ * in favor of {@link MMapDirectory}. It will be removed in future versions 
+ * of Lucene.
  */
+@Deprecated
 public class RAMDirectory extends BaseDirectory implements Accountable {
   protected final Map<String,RAMFile> fileMap = new ConcurrentHashMap<>();
   protected final AtomicLong sizeInBytes = new AtomicLong();

lucene/core/src/java/org/apache/lucene/store/RAMFile.java

@@ -24,7 +24,13 @@ import org.apache.lucene.util.Accountable;
 
 /** 
  * Represents a file in RAM as a list of byte[] buffers.
- * @lucene.internal */
+ * 
+ * @lucene.internal 
+ * @deprecated This class uses inefficient synchronization and is discouraged
+ * in favor of {@link MMapDirectory}. It will be removed in future versions 
+ * of Lucene.
+ */
+@Deprecated
 public class RAMFile implements Accountable {
   protected final ArrayList<byte[]> buffers = new ArrayList<>();
   long length;

lucene/core/src/java/org/apache/lucene/store/RAMInputStream.java

@@ -22,9 +22,15 @@ import java.io.IOException;
 
 import static org.apache.lucene.store.RAMOutputStream.BUFFER_SIZE;
 
-/** A memory-resident {@link IndexInput} implementation. 
- *  
- *  @lucene.internal */
+/** 
+ * A memory-resident {@link IndexInput} implementation. 
+ *
+ * @lucene.internal 
+ * @deprecated This class uses inefficient synchronization and is discouraged
+ * in favor of {@link MMapDirectory}. It will be removed in future versions 
+ * of Lucene.
+ */
+@Deprecated
 public class RAMInputStream extends IndexInput implements Cloneable {
 
   private final RAMFile file;

lucene/core/src/java/org/apache/lucene/store/RAMOutputStream.java

@@ -30,7 +30,11 @@ import org.apache.lucene.util.Accountables;
  * A memory-resident {@link IndexOutput} implementation.
  *
  * @lucene.internal
+ * @deprecated This class uses inefficient synchronization and is discouraged
+ * in favor of {@link MMapDirectory}. It will be removed in future versions 
+ * of Lucene.
  */
+@Deprecated
 public class RAMOutputStream extends IndexOutput implements Accountable {
   static final int BUFFER_SIZE = 1024;