MXS-2592 Add configuration for session specific in-memory log

When enabled each session will write log messages in the in-memory log.
If session ends in error this log is written to the actual log in disk.

server/core/config.cc

@@ -160,6 +160,7 @@ const char CN_SERVER[] = "server";
 const char CN_SERVICES[] = "services";
 const char CN_SERVICE[] = "service";
 const char CN_SESSIONS[] = "sessions";
+const char CN_SESSION_TRACE[] = "session_trace";
 const char CN_SESSION_TRACK_TRX_STATE[] = "session_track_trx_state";
 const char CN_SKIP_PERMISSION_CHECKS[] = "skip_permission_checks";
 const char CN_SOCKET[] = "socket";
@@ -317,6 +318,7 @@ const MXS_MODULE_PARAM config_service_params[] =
     {CN_RETRY_ON_FAILURE,              MXS_MODULE_PARAM_BOOL,   "true"},
     {CN_SESSION_TRACK_TRX_STATE,       MXS_MODULE_PARAM_BOOL,   "false"},
     {CN_RETAIN_LAST_STATEMENTS,        MXS_MODULE_PARAM_INT,    "-1"},
+    {CN_SESSION_TRACE,                 MXS_MODULE_PARAM_INT,    "0"},
     {NULL}
 };
 
@@ -2602,6 +2604,21 @@ static int handle_global_item(const char* name, const char* value)
             return 0;
         }
     }
+    else if (strcmp(name, CN_SESSION_TRACE) == 0)
+    {
+        char* endptr;
+        int intval = strtol(value, &endptr, 0);
+        if (*endptr == '\0' && intval >= 0)
+        {
+            session_set_session_trace(intval);
+            mxb_log_set_session_trace(true);
+        }
+        else
+        {
+            MXS_ERROR("Invalid value for '%s': %s", CN_SESSION_TRACE, value);
+            return 0;
+        }
+    }
     else if (strcmp(name, CN_LOAD_PERSISTED_CONFIGS) == 0)
     {
         int b = config_truth_value(value);

server/core/gateway.cc

@@ -432,6 +432,7 @@ static void sigfatal_handler(int i)
         if (dcb->session)
         {
             session_dump_statements(dcb->session);
+            session_dump_log(dcb->session);
         }
     }
 

server/core/internal/session.hh

@@ -97,7 +97,7 @@ public:
     };
 
     typedef std::deque<QueryInfo> QueryInfos;
-
+    using Log = std::deque<std::string>;
     using FilterList = std::vector<SessionFilter>;
 
     Session(SERVICE* service);
@@ -121,8 +121,11 @@ public:
     void book_server_response(SERVER* pServer, bool final_response);
     void book_last_as_complete();
     void reset_server_bookkeeping();
+    void append_session_log(std::string);
+    void dump_session_log();
 
     json_t* queries_as_json() const;
+    json_t* log_as_json() const;
 
     void link_backend_dcb(DCB* dcb)
     {
@@ -148,6 +151,7 @@ private:
     int               m_current_query = -1;     /*< The index of the current query */
     DCBSet            m_dcb_set;                /*< Set of associated backend DCBs */
     uint32_t          m_retain_last_statements; /*< How many statements be retained */
+    Log               m_log;                    /*< Session specific in-memory log */
 };
 }
 

server/core/log.cc

@@ -47,13 +47,22 @@ size_t mxs_get_context(char* buffer, size_t len)
 
     return len;
 }
+
+void mxs_log_in_memory(const char* msg, size_t len)
+{
+    MXS_SESSION* session = session_get_current();
+    if (session)
+    {
+        session_append_log(session, msg);
+    }
+}
 }
 
 bool mxs_log_init(const char* ident, const char* logdir, mxs_log_target_t target)
 {
     mxb::Logger::set_ident("MariaDB MaxScale");
 
-    return mxb_log_init(ident, logdir, LOGFILE_NAME, target, mxs_get_context);
+    return mxb_log_init(ident, logdir, LOGFILE_NAME, target, mxs_get_context, mxs_log_in_memory);
 }
 
 namespace

server/core/session.cc

@@ -62,11 +62,13 @@ struct
     uint64_t next_session_id;
     uint32_t retain_last_statements;
     session_dump_statements_t dump_statements;
+    uint32_t session_trace;
 } this_unit =
 {
     1,
     0,
-    SESSION_DUMP_STATEMENTS_NEVER
+    SESSION_DUMP_STATEMENTS_NEVER,
+    0
 };
 
 static struct session dummy_session()
@@ -909,6 +911,9 @@ json_t* session_json_data(const Session* session, const char* host)
     json_t* queries = session->queries_as_json();
     json_object_set_new(attr, "queries", queries);
 
+    json_t* log = session->log_as_json();
+    json_object_set_new(attr, "log", log);
+
     json_object_set_new(data, CN_ATTRIBUTES, attr);
     json_object_set_new(data, CN_LINKS, mxs_json_self_link(host, CN_SESSIONS, ss.str().c_str()));
 
@@ -1111,6 +1116,32 @@ void session_dump_statements(MXS_SESSION* session)
     pSession->dump_statements();
 }
 
+void session_set_session_trace(uint32_t value)
+{
+    this_unit.session_trace = value;
+}
+
+uint32_t session_get_session_trace()
+{
+    return this_unit.session_trace;
+}
+
+void session_append_log(MXS_SESSION* pSession, const char* log)
+{
+    // Ignore dummy and listener sessions
+    if (pSession->state != SESSION_STATE_DUMMY
+        && pSession->state != SESSION_STATE_LISTENER
+        && pSession->state != SESSION_STATE_LISTENER_STOPPED)
+    {
+        static_cast<Session*>(pSession)->append_session_log(std::string(log));
+    }
+}
+
+void session_dump_log(MXS_SESSION* pSession)
+{
+    static_cast<Session*>(pSession)->dump_session_log();
+}
+
 class DelayedRoutingTask
 {
     DelayedRoutingTask(const DelayedRoutingTask&) = delete;
@@ -1365,6 +1396,18 @@ json_t* Session::queries_as_json() const
     return pQueries;
 }
 
+json_t* Session::log_as_json() const
+{
+    json_t* pLog = json_array();
+
+    for (const auto& i : m_log)
+    {
+        json_array_append_new(pLog, json_string(i.c_str()));
+    }
+
+    return pLog;
+}
+
 bool Session::setup_filters(Service* service)
 {
     for (const auto& a : service->get_filters())
@@ -1724,3 +1767,28 @@ void Session::QueryInfo::reset_server_bookkeeping()
     m_completed.tv_nsec = 0;
     m_complete = false;
 }
+
+void Session::append_session_log(std::string log)
+{
+    m_log.push_front(log);
+
+    if (m_log.size() >= this_unit.session_trace)
+    {
+        m_log.pop_back();
+    }
+}
+
+void Session::dump_session_log()
+{
+    if (!(m_log.empty()))
+    {
+        std::string log;
+
+        for (const auto& s : m_log)
+        {
+            log += s;
+        }
+
+        MXS_NOTICE("Session log for session (%" PRIu64"): \n%s ", ses_id, log.c_str());
+    }
+}