First stage of optimizing in-memory string column representation: des…

…erialize string column protobuf msg into packed byte array with offsets.

src/edu/washington/escience/myria/column/StringPackedColumn.java

@@ -0,0 +1,60 @@
+package edu.washington.escience.myria.column;
+
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * A column of String values, packed into a UTF-8 encoded byte array.
+ * 
+ * 
+ */
+public final class StringPackedColumn extends StringColumn {
+  /** Required for Java serialization. */
+  private static final long serialVersionUID = 1L;
+  /** A read-only buffer containing the packed UTF-8 character data. */
+  private final ByteBuffer data;
+  /** Contains the number of bytes in data. */
+  private final int numBytes;
+  /** Contains the offset of each string in order. */
+  private final int[] offsets;
+
+  /**
+   * Constructs a new column.
+   * 
+   * @param data the data
+   * @param offsets offsets of strings within data column
+   * */
+  public StringPackedColumn(final ByteBuffer data, final int numBytes, final int[] offsets) {
+    this.data = data;
+    this.numBytes = numBytes;
+    this.offsets = offsets;
+  }
+
+  /**
+   * Returns the element at the specified row in this column.
+   * 
+   * @param row row of element to return.
+   * @return the element at the specified row in this column.
+   */
+  @Override
+  public String getString(final int row) {
+    Preconditions.checkElementIndex(row, size());
+    int len;
+    if (row == offsets.length - 1) {
+      len = numBytes - offsets[row];
+    } else {
+      len = offsets[row + 1] - offsets[row];
+    }
+    byte[] strBytes = new byte[len];
+    data.position(offsets[row]);
+    data.get(strBytes, 0, len);
+    return new String(strBytes, StandardCharsets.UTF_8);
+  }
+
+  @Override
+  public int size() {
+    return offsets.length;
+  }
+}

src/edu/washington/escience/myria/column/builder/StringColumnBuilder.java

@@ -1,18 +1,20 @@
 package edu.washington.escience.myria.column.builder;
 
 import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
 import java.sql.ResultSet;
 import java.sql.SQLException;
-import java.util.List;
 import java.util.Objects;
 
 import com.almworks.sqlite4java.SQLiteException;
 import com.almworks.sqlite4java.SQLiteStatement;
 import com.google.common.base.Preconditions;
+import com.google.common.primitives.Ints;
 
 import edu.washington.escience.myria.Type;
 import edu.washington.escience.myria.column.StringArrayColumn;
 import edu.washington.escience.myria.column.StringColumn;
+import edu.washington.escience.myria.column.StringPackedColumn;
 import edu.washington.escience.myria.column.mutable.StringMutableColumn;
 import edu.washington.escience.myria.proto.DataProto.ColumnMessage;
 import edu.washington.escience.myria.proto.DataProto.StringColumnMessage;
@@ -66,14 +68,10 @@ public static StringColumn buildFromProtobuf(final ColumnMessage message, final
         "Trying to construct StringColumn from non-STRING ColumnMessage %s", message.getType());
     Preconditions.checkArgument(message.hasStringColumn(), "ColumnMessage has type STRING but no StringColumn");
     final StringColumnMessage stringColumn = message.getStringColumn();
-    List<Integer> startIndices = stringColumn.getStartIndicesList();
-    List<Integer> endIndices = stringColumn.getEndIndicesList();
-    String[] newData = new String[numTuples];
-    String allStrings = stringColumn.getData().toStringUtf8();
-    for (int i = 0; i < numTuples; i++) {
-      newData[i] = allStrings.substring(startIndices.get(i), endIndices.get(i));
-    }
-    return new StringColumnBuilder(newData, numTuples).build();
+    int numBytes = stringColumn.getData().size();
+    ByteBuffer data = stringColumn.getData().asReadOnlyByteBuffer();
+    int[] offsets = Ints.toArray(stringColumn.getStartIndicesList());
+    return new StringPackedColumn(data, numBytes, offsets);
   }
 
   @Override