Make parallel scan thread count configurable

modules/api/src/main/java/org/apache/fluo/api/config/FluoConfiguration.java

@@ -188,6 +188,9 @@ public class FluoConfiguration extends SimpleConfiguration {
   public static final String WORKER_NUM_THREADS_PROP = WORKER_PREFIX + ".num.threads";
   public static final int WORKER_NUM_THREADS_DEFAULT = 10;
 
+  public static final String PARALLEL_SCAN_THREADS_PROP = FLUO_PREFIX + ".scan.num.threads";
+  public static final int NUM_PARALLEL_SCAN_THREADS_DEFAULT = 1;
+
   // Loader properties
   private static final String LOADER_PREFIX = FLUO_PREFIX + ".loader";
   public static final String LOADER_NUM_THREADS_PROP = LOADER_PREFIX + ".num.threads";
@@ -634,6 +637,29 @@ public int getWorkerThreads() {
     return getPositiveInt(WORKER_NUM_THREADS_PROP, WORKER_NUM_THREADS_DEFAULT);
   }
 
+  /**
+   * Sets the number of threads used to execute parallel scans, must be positive. The default is
+   * {@value #NUM_PARALLEL_SCAN_THREADS_DEFAULT} thread. Sets this value in the property
+   * {@value #PARALLEL_SCAN_THREADS_PROP}
+   *
+   * @param numThreads The number of threads to use, must be positive
+   * @since 2.0.0
+   */
+  public FluoConfiguration setNumParallelScanThreads(int numThreads) {
+    return setPositiveInt(PARALLEL_SCAN_THREADS_PROP, numThreads);
+  }
+
+  /**
+   * Gets the value of the property {@value #PARALLEL_SCAN_THREADS_PROP} if set otherwise returns
+   * {@value #NUM_PARALLEL_SCAN_THREADS_DEFAULT}
+   *
+   * @return The number of threads used for parallel scans.
+   * @since 2.0.0
+   */
+  public int getNumParallelScanThreads() {
+    return getPositiveInt(PARALLEL_SCAN_THREADS_PROP, NUM_PARALLEL_SCAN_THREADS_DEFAULT);
+  }
+
   /**
    * @deprecated since 1.1.0. Replaced by {@link #setObserverProvider(String)} and
    *             {@link #getObserverProvider()}

modules/core/src/main/java/org/apache/fluo/core/impl/ParallelSnapshotScanner.java

@@ -116,9 +116,9 @@ private BatchScanner setupBatchScanner() {
 
     BatchScanner scanner;
     try {
-      // TODO hardcoded number of threads!
-      // one thread is probably good.. going for throughput
-      scanner = env.getAccumuloClient().createBatchScanner(env.getTable(), this.authorizations, 1);
+      scanner =
+          env.getAccumuloClient().createBatchScanner(env.getTable(), env.getAuthorizations(),
+                  env.getConfiguration().getNumParallelScanThreads());
     } catch (TableNotFoundException e) {
       throw new RuntimeException(e);
     }