diff --git a/examples/examplefilter.cc b/examples/examplefilter.cc
index 6e7d2c282..87993670b 100644
--- a/examples/examplefilter.cc
+++ b/examples/examplefilter.cc
@@ -12,28 +12,47 @@
  */
 
 // All log messages from this module are prefixed with this
-#define MXS_MODULE_NAME "examplefilter"
+#define MXS_MODULE_NAME "examplecppfilter"
+
+/*
+ * To use the filter in a configuration, add the following section to the config file:
+ * [ExampleFilter]
+ * type=filter
+ * module=examplecppfilter
+ * global_counts=true
+ *
+ * Then add the filter to a service:
+ * [Read-Write-Service]
+ * .
+ * .
+ * filters=ExampleFilter
+ */
 
 #include "examplefilter.hh"
 
+static const char CN_COUNT_GLOBALS[] = "global_counts";
+
 // This declares a module in MaxScale
 extern "C" MXS_MODULE* MXS_CREATE_MODULE()
 {
+    static const char DESC[] = "An example filter that counts the number of queries and replies "
+                               "it has routed";
     static MXS_MODULE info =
     {
         MXS_MODULE_API_FILTER,
         MXS_MODULE_IN_DEVELOPMENT,
         MXS_FILTER_VERSION,
-        "An example filter that does nothing",
+        DESC,
         "V1.0.0",
-        RCAP_TYPE_NONE,
+        RCAP_TYPE_STMT_INPUT,                   // See getCapabilities() below
         &ExampleFilter::s_object,               // This is defined in the MaxScale filter template
         NULL,                                   /* Process init. */
         NULL,                                   /* Process finish. */
         NULL,                                   /* Thread init. */
         NULL,                                   /* Thread finish. */
         {
-            {"an_example_parameter",          MXS_MODULE_PARAM_STRING,"a-default-value"},
+            {"an_example_parameter",          MXS_MODULE_PARAM_STRING, "a-default-value"},
+            {CN_COUNT_GLOBALS,                MXS_MODULE_PARAM_BOOL,   "true"},
             {MXS_END_MODULE_PARAMS}
         }
     };
@@ -41,8 +60,9 @@ extern "C" MXS_MODULE* MXS_CREATE_MODULE()
     return &info;
 }
 
-ExampleFilter::ExampleFilter()
+ExampleFilter::ExampleFilter(const MXS_CONFIG_PARAMETER* pParams)
 {
+    m_collect_global_counts = config_get_bool(pParams, CN_COUNT_GLOBALS);
 }
 
 ExampleFilter::~ExampleFilter()
@@ -52,27 +72,58 @@ ExampleFilter::~ExampleFilter()
 // static
 ExampleFilter* ExampleFilter::create(const char* zName, MXS_CONFIG_PARAMETER* pParams)
 {
-    return new ExampleFilter();
+    return new ExampleFilter(pParams);
 }
 
 ExampleFilterSession* ExampleFilter::newSession(MXS_SESSION* pSession)
 {
-    return ExampleFilterSession::create(pSession, this);
+    return ExampleFilterSession::create(pSession, *this);
 }
 
 // static
 void ExampleFilter::diagnostics(DCB* pDcb) const
 {
+    int queries = m_total_queries.load(std::memory_order_relaxed);
+    int replies = m_total_replies.load(std::memory_order_relaxed);
+    dcb_printf(pDcb, "\t\tTotal queries            %i\n", queries);
+    dcb_printf(pDcb, "\t\tTotal replies            %i\n", replies);
 }
 
 // static
 json_t* ExampleFilter::diagnostics_json() const
 {
-    return NULL;
+    json_t* rval = json_object();
+    int queries = m_total_queries.load(std::memory_order_relaxed);
+    int replies = m_total_replies.load(std::memory_order_relaxed);
+    json_object_set_new(rval, "total_queries", json_integer(queries));
+    json_object_set_new(rval, "total_replies", json_integer(replies));
+    return rval;
 }
 
 // static
 uint64_t ExampleFilter::getCapabilities()
 {
-    return RCAP_TYPE_NONE;
+    // Tells the protocol that the filter expects complete queries from client, that is, a query cannot be
+    // sent in parts.
+    return RCAP_TYPE_STMT_INPUT;
+
+    // Try the following to also expect replies to be complete. This can cause problems if the server sends
+    // a really big (e.g. 1 GB) resultset.
+    // return RCAP_TYPE_STMT_INPUT | RCAP_TYPE_RESULTSET_OUTPUT;
 }
+
+void ExampleFilter::query_seen()
+{
+    if (m_collect_global_counts)
+    {
+        m_total_queries.fetch_add(1, std::memory_order_relaxed);
+    }
+}
+
+void ExampleFilter::reply_seen()
+{
+    if (m_collect_global_counts)
+    {
+        m_total_replies.fetch_add(1, std::memory_order_relaxed);
+    }
+}
\ No newline at end of file
diff --git a/examples/examplefilter.hh b/examples/examplefilter.hh
index d441c7908..8faf2651a 100644
--- a/examples/examplefilter.hh
+++ b/examples/examplefilter.hh
@@ -13,9 +13,16 @@
 #pragma once
 
 #include <maxscale/ccdefs.hh>
+#include <atomic>
 #include <maxscale/filter.hh>
 #include "examplefiltersession.hh"
 
+/**
+ * Defines general data for the filter. This object is generated when MaxScale starts and deleted at
+ * shutdown. When MaxScale is routing queries, this object may be accessed from multiple threads
+ * concurrently. This should be considered if the object contains fields that are unsafe to
+ * access/modify concurrently.
+ */
 class ExampleFilter : public maxscale::Filter<ExampleFilter, ExampleFilterSession>
 {
     // Prevent copy-constructor and assignment operator usage
@@ -25,22 +32,63 @@ class ExampleFilter : public maxscale::Filter<ExampleFilter, ExampleFilterSessio
 public:
     ~ExampleFilter();
 
-    // Creates a new filter instance
+    /**
+     * Creates a new filter instance. A separate function from the ctor is used so that NULL can be
+     * returned on failure.
+     *
+     * @param zName The name given to the filter in the configuration file. Can be stored if required for
+     * e.g. log messages.
+     * @param ppParams Configuration parameters parsed from the configuration file
+     * @return The object on success, NULL on failure. Failure is typically caused by an invalid
+     * configuration parameter.
+     */
     static ExampleFilter* create(const char* zName, MXS_CONFIG_PARAMETER* ppParams);
 
-    // Creates a new session for this filter
+    /*
+     * Creates a new session for this filter. This is called when a new client connects.
+     *
+     * @param pSession The generic MaxScale session object.
+     * @return The new session, or NULL on failure.
+     */
     ExampleFilterSession* newSession(MXS_SESSION* pSession);
 
-    // Print diagnostics to a DCB
+    /*
+     * Print diagnostics to a DCB. This is called when the admin tool MaxAdmin asks for the status of this
+     * filter. Run MaxAdmin with "./maxadmin show filters" in the MaxScale binary directory.
+     *
+     * @param pDcb The connection descriptor to print diagnostic to
+     */
     void diagnostics(DCB* pDcb) const;
 
-    // Returns JSON form diagnostic data
+    /*
+     * Returns JSON form diagnostic data. This is called when the admin tool MaxCtrl asks for the status
+     * of this filter. Run MaxCtrl with "./maxctrl show filters" in the MaxScale binary directory.
+     *
+     * @return Json object
+     */
     json_t* diagnostics_json() const;
 
-    // Get filter capabilities
+    /*
+     * Get filter capabilities. This is used by protocol code to find out what kind of data the filter
+     * expects.
+     *
+     * @return Capabilities as a bitfield
+     */
     uint64_t getCapabilities();
 
+    // Specific to ExampleFilter. Called by a session when it sees a query.
+    void query_seen();
+
+    // Specific to ExampleFilter. Called by a session when it sees a reply.
+    void reply_seen();
+
 private:
-    // Used in the create function
-    ExampleFilter();
+    // Used by the create function
+    ExampleFilter(const MXS_CONFIG_PARAMETER* pParams);
+
+    // The fields are specific to ExampleFilter.
+    std::atomic<int> m_total_queries {0}; /**< How many queries has this filter seen */
+    std::atomic<int> m_total_replies {0}; /**< How many replies has this filter seen */
+
+    bool m_collect_global_counts {false}; /**< Should sessions manipulate the total counts */
 };
diff --git a/examples/examplefiltersession.cc b/examples/examplefiltersession.cc
index 22f2fecd0..2b6e6b949 100644
--- a/examples/examplefiltersession.cc
+++ b/examples/examplefiltersession.cc
@@ -17,8 +17,10 @@
 #include "examplefiltersession.hh"
 #include "examplefilter.hh"
 
-ExampleFilterSession::ExampleFilterSession(MXS_SESSION* pSession)
+ExampleFilterSession::ExampleFilterSession(MXS_SESSION* pSession, ExampleFilter& filter)
     : mxs::FilterSession(pSession)
+    , m_filter(filter)
+    , m_session_id(pSession->ses_id)
 {
 }
 
@@ -27,21 +29,31 @@ ExampleFilterSession::~ExampleFilterSession()
 }
 
 // static
-ExampleFilterSession* ExampleFilterSession::create(MXS_SESSION* pSession, const ExampleFilter* pFilter)
+ExampleFilterSession* ExampleFilterSession::create(MXS_SESSION* pSession, ExampleFilter& filter)
 {
-    return new ExampleFilterSession(pSession);
+    return new ExampleFilterSession(pSession, filter);
 }
 
 void ExampleFilterSession::close()
 {
+    // When the session is closed, report the numbers to the log.
+    MXS_NOTICE("Session %lu routed %i queries and %i replies.", m_session_id, m_queries, m_replies);
 }
 
 int ExampleFilterSession::routeQuery(GWBUF* pPacket)
 {
+    m_queries++;
+    m_filter.query_seen();
+
+    // Pass the query forward.
     return mxs::FilterSession::routeQuery(pPacket);
 }
 
 int ExampleFilterSession::clientReply(GWBUF* pPacket)
 {
+    m_replies++;
+    m_filter.reply_seen();
+
+    // Pass the reply forward.
     return mxs::FilterSession::clientReply(pPacket);
 }
diff --git a/examples/examplefiltersession.hh b/examples/examplefiltersession.hh
index 2dcb757d0..ced7116fd 100644
--- a/examples/examplefiltersession.hh
+++ b/examples/examplefiltersession.hh
@@ -17,6 +17,11 @@
 
 class ExampleFilter;
 
+/*
+ * Defines session-specific data for this filter. An object of this class is created when a client connects
+ * and deleted on disconnect. The object is only accessed from one thread because sessions are locked to
+ * a thread when created.
+ */
 class ExampleFilterSession : public maxscale::FilterSession
 {
     // Prevent copy-constructor and assignment operator usage
@@ -26,19 +31,48 @@ class ExampleFilterSession : public maxscale::FilterSession
 public:
     ~ExampleFilterSession();
 
-    // Called when a client session has been closed
+    // Called when a client session has been closed. Destructor will be called right after.
     void close();
 
-    // Create a new filter session
-    static ExampleFilterSession* create(MXS_SESSION* pSession, const ExampleFilter* pFilter);
+    /**
+     * Called by ExampleFilter::newSession() to create the session.
+     *
+     * @param pSession pSession The generic MaxScale session object
+     * @param pFilter The shared filter object
+     * @return A new session or NULL on failure
+     */
+    static ExampleFilterSession* create(MXS_SESSION* pSession, ExampleFilter& pFilter);
 
-    // Handle a query from the client
+    /**
+     * Handle a query from the client. This is called when the client sends a query and the query has not
+     * been blocked by any previous component in the query processing chain. The filter should do its own
+     * processing and then send the query to the next component. If the query comes in multiple packets,
+     * this is called for each packet.
+     *
+     * @param pPacket Packet containing the query, or at least a part of it
+     * @return 0 on success. This typically depends on the later stages of the query processing chain.
+     */
     int routeQuery(GWBUF* pPacket);
 
-    // Handle a reply from server
+
+    /**
+     * Handle a reply from server. The reply typically contains a resultset or a response to a command.
+     * The filter should do its own processing and then send the query to the next component.
+     * If the reply comes in multiple packets, this is called for each packet. The processing chain for
+     * replies is the same as for queries, just walked in the opposite direction.
+     *
+     * @param pPacket Packet containing results
+     * @return 0 on success. This typically depends on the later stages of the reply processing chain.
+     */
     int clientReply(GWBUF* pPacket);
 
 private:
     // Used in the create function
-    ExampleFilterSession(MXS_SESSION* pSession);
+    ExampleFilterSession(MXS_SESSION* pSession, ExampleFilter& filter);
+
+    ExampleFilter& m_filter;   /**< Shared filter data */
+
+    uint64_t m_session_id {0}; /**< Session id */
+    int      m_queries {0};    /**< How many queries has this session seen */
+    int      m_replies {0};    /**< How many replies has this session seen */
 };