Logs a compact description of druid filters.

--A map is logged that describes the structure of the filter being sent
to druid. For each filter it includes a count of the number of instances
of that filter.

fili-core/src/main/java/com/yahoo/bard/webservice/druid/model/filter/ComplexFilter.java

@@ -0,0 +1,19 @@
+// Copyright 2016 Yahoo Inc.
+// Licensed under the terms of the Apache license. Please see LICENSE.md file distributed with this work for terms.
+package com.yahoo.bard.webservice.druid.model.filter;
+
+import java.util.List;
+
+/**
+ * A Druid filter that is defined by applying an operation to at least one other filter. For example, {@code not} and
+ * {@code and} filters are complex. A {@code selector} filter is not.
+ */
+public interface ComplexFilter {
+
+    /**
+     * Returns the filters that are operated on by this filter.
+     *
+     * @return The filters operated on by this filter
+     */
+    List<Filter> getFields();
+}

fili-core/src/main/java/com/yahoo/bard/webservice/logging/blocks/DruidFilterInfo.java

@@ -0,0 +1,59 @@
+// Copyright 2016 Yahoo Inc.
+// Licensed under the terms of the Apache license. Please see LICENSE.md file distributed with this work for terms.
+package com.yahoo.bard.webservice.logging.blocks;
+
+import com.yahoo.bard.webservice.druid.model.filter.ComplexFilter;
+import com.yahoo.bard.webservice.druid.model.filter.Filter;
+import com.yahoo.bard.webservice.logging.LogInfo;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+
+import java.util.ArrayDeque;
+import java.util.Collections;
+import java.util.Deque;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * Logs some structural data about the filter sent to Druid, without actually logging the entire (potentially massive)
+ * filter.
+ */
+@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
+public class DruidFilterInfo implements LogInfo {
+
+    protected final Map<String, Long> numEachFilterType;
+
+    /**
+     * Constructor.
+     *
+     * @param filter  The filter that needs to be analyzed
+     */
+    public DruidFilterInfo(Filter filter) {
+        numEachFilterType = buildFilterCount(filter);
+    }
+
+    /**
+     * Performs a DFS search of the filter tree, populating the specified map with the number of instances of each
+     * filter type appearing in the filter.
+     *
+     * @param filter  The filter that needs to be traversed
+     *
+     * @return A map containing a count of each type of filter
+     */
+    private Map<String, Long> buildFilterCount(Filter filter) {
+        if (filter == null) {
+            return Collections.emptyMap();
+        }
+        Map<String, Long> filterTypeCounter = new LinkedHashMap<>();
+        Deque<Filter> filterStack = new ArrayDeque<>();
+        filterStack.add(filter);
+        while (!filterStack.isEmpty()) {
+            Filter currentFilter = filterStack.pop();
+            filterTypeCounter.merge(currentFilter.getClass().getSimpleName(), 1L, (old, increment) -> old + increment);
+            if (currentFilter instanceof ComplexFilter) {
+                filterStack.addAll(((ComplexFilter) currentFilter).getFields());
+            }
+        }
+        return filterTypeCounter;
+    }
+}

fili-core/src/main/java/com/yahoo/bard/webservice/web/endpoints/DataServlet.java

@@ -32,6 +32,7 @@
 import com.yahoo.bard.webservice.logging.RequestLog;
 import com.yahoo.bard.webservice.logging.blocks.BardQueryInfo;
 import com.yahoo.bard.webservice.logging.blocks.DataRequest;
+import com.yahoo.bard.webservice.logging.blocks.DruidFilterInfo;
 import com.yahoo.bard.webservice.table.Table;
 import com.yahoo.bard.webservice.util.Either;
 import com.yahoo.bard.webservice.web.DataApiRequest;
@@ -407,6 +408,7 @@ public void getData(
 
             RequestLog.switchTiming("logRequestMetrics");
             logRequestMetrics(apiRequest, readCache, druidQuery);
+            RequestLog.record(new DruidFilterInfo(apiRequest.getFilter()));
             RequestLog.switchTiming(REQUEST_WORKFLOW_TIMER);
 
             // Process the request

fili-core/src/test/groovy/com/yahoo/bard/webservice/logging/blocks/DruidFilterInfoSpec.groovy

@@ -0,0 +1,36 @@
+package com.yahoo.bard.webservice.logging.blocks
+
+import com.yahoo.bard.webservice.data.dimension.Dimension
+import com.yahoo.bard.webservice.druid.model.filter.AndFilter
+import com.yahoo.bard.webservice.druid.model.filter.Filter
+import com.yahoo.bard.webservice.druid.model.filter.NotFilter
+import com.yahoo.bard.webservice.druid.model.filter.OrFilter
+import com.yahoo.bard.webservice.druid.model.filter.SelectorFilter
+
+import spock.lang.Shared
+import spock.lang.Specification
+import spock.lang.Unroll
+
+class DruidFilterInfoSpec extends Specification {
+
+    @Shared Filter selector = new SelectorFilter(Stub(Dimension), "value")
+
+    static final String SELECTOR_NAME = SelectorFilter.class.simpleName
+    static final String AND_NAME = AndFilter.class.simpleName
+    static final String OR_NAME = OrFilter.class.simpleName
+    static final String NOT_NAME = NotFilter.class.simpleName
+
+    @Unroll
+    def "The DruidFilterInfo correctly analyzes #filter"() {
+        expect:
+        new DruidFilterInfo(filter).numEachFilterType == expectedMap
+
+        where:
+        filter                                                                                                  | expectedMap
+        null                                                                                                    | [:]
+        selector                                                                                                | [(SELECTOR_NAME): 1L]
+        new AndFilter([selector, selector])                                                                     | [(AND_NAME): 1L, (SELECTOR_NAME): 2L]
+        new NotFilter(new AndFilter([selector, selector]))                                                      | [(NOT_NAME): 1L, (AND_NAME): 1L, (SELECTOR_NAME): 2L]
+        new OrFilter([new AndFilter([selector, selector]), new NotFilter(new AndFilter([selector, selector]))]) | [(OR_NAME): 1L, (AND_NAME): 2L, (NOT_NAME): 1L, (SELECTOR_NAME): 4L]
+    }
+}