MXS-2555 Implement cache eviction (or query re-measurment) strategy

server/modules/routing/smartrouter/performance.cc

@@ -13,44 +13,6 @@
 
 #include "performance.hh"
 
-#include <cstdio>
-#include <fstream>
-#include <mutex>
-
-const std::string file_version = "Alpha";   // if a file has a different version string, discard it.
-
-CanonicalPerformance::CanonicalPerformance()
-    : m_nChanges(0)
-{
-}
-
-bool CanonicalPerformance::insert(const std::string& canonical, const PerformanceInfo& perf)
-{
-    bool saved = m_perfs.insert({canonical, perf}).second;
-    m_nChanges += saved;
-
-    return saved;
-}
-
-bool CanonicalPerformance::remove(const std::string& canonical)
-{
-    auto erased = m_perfs.erase(canonical);
-    m_nChanges += erased;
-    return erased;
-}
-
-PerformanceInfo CanonicalPerformance::find(const std::string& canonical)
-{
-    auto it = m_perfs.find(canonical);
-    return it == m_perfs.end() ? PerformanceInfo() : it->second;
-}
-
-void CanonicalPerformance::clear()
-{
-    m_perfs.clear();
-    m_nChanges = 0;
-}
-
 std::string show_some(const std::string& str, int nchars)
 {
     int sz = str.length();
@@ -64,7 +26,6 @@ std::string show_some(const std::string& str, int nchars)
     }
 }
 
-
 // These are TODOs for the GA version. The Beta version will not have persistence.
 // 1. Read the file once at startup. There might also be a need to do cleanup
 //    of the file if the configuration has changed.
@@ -78,11 +39,3 @@ std::string show_some(const std::string& str, int nchars)
 //    probably be dropped immediately.
 // 6. Save all data at shutdown.
 // Start using xxhash
-//
-// Expiration rules. At least these rules should be implemented:
-// 1. Since the various engines have different setup times during the first few queries,
-//    this should be taken into account (not implemented).
-// 2. Expire entries after X minutes.
-// 3. If the measured time is very different from the stored one (+/20%),
-//    expire the entry (not implemented).
-// More rules can be found out by testing.

server/modules/routing/smartrouter/performance.hh

@@ -19,8 +19,8 @@
 
 #include <unordered_map>
 
-/** Class PerformanceInfo is a basic structure for storing a Host and Duration pair, along with
+/** PerformanceInfo is a class that on the one hand provides routeQuery() with performance/routing
- *  the time it was created.
+ *  information and on the other has data for class SmartRouter to manage the life-time of a measurment.
  */
 class PerformanceInfo
 {
@@ -40,38 +40,24 @@ public:
     /** Duration since this PerformanceInfo was created
      */
     maxbase::Duration age() const;
+
+    /** Managed and used only by class SmartRouter. */
+    void   set_eviction_schedule(size_t es);
+    size_t eviction_schedule() const;
+
+    /** Managed and used only by class SmartRouter. */
+    void set_updating(bool val);
+    bool is_updating() const;
 private:
     maxbase::Host     m_host;
     maxbase::Duration m_duration;
 
+    int  m_eviction_schedule = 0;
+    bool m_updating = false;
+
     maxbase::TimePoint m_creation_time = maxbase::Clock::now();
 };
 
-/** class CanonicalPerformance holds the performance
- *  info gathered since the start of Maxscale.
- *  The Beta release will not perist to file.
- */
-class CanonicalPerformance
-{
-public:
-    explicit CanonicalPerformance();
-
-    /** Insert if not already inserted and return true, else false. */
-    bool insert(const std::string& canonical, const PerformanceInfo& perf);
-
-    /** Remove if entry exists and return true, else false. */
-    bool remove(const std::string& canonical);
-
-    /** If entry does not exists, returned PerformanceInfo::is_valid()==false */
-    PerformanceInfo find(const std::string& canonical);
-
-    void clear();
-private:
-    std::unordered_map<std::string, PerformanceInfo> m_perfs;
-
-    mutable int m_nChanges;
-};
-
 // For logging. Shortens str to nchars and adds "..." TODO move somewhere more appropriate
 std::string show_some(const std::string& str, int nchars = 70);
 
@@ -106,3 +92,23 @@ inline maxbase::Duration PerformanceInfo::age() const
 {
     return maxbase::Clock::now() - m_creation_time;
 }
+
+inline void PerformanceInfo::set_eviction_schedule(size_t es)
+{
+    m_eviction_schedule = es;
+}
+
+inline size_t PerformanceInfo::eviction_schedule() const
+{
+    return m_eviction_schedule;
+}
+
+inline void PerformanceInfo::set_updating(bool val)
+{
+    m_updating = val;
+}
+
+inline bool PerformanceInfo::is_updating() const
+{
+    return m_updating;
+}

server/modules/routing/smartrouter/smartrouter.cc

@@ -197,29 +197,69 @@ uint64_t SmartRouter::getCapabilities()
     return RCAP_TYPE_TRANSACTION_TRACKING | RCAP_TYPE_CONTIGUOUS_INPUT | RCAP_TYPE_CONTIGUOUS_OUTPUT;
 }
 
+// Eviction schedule
+// Two reasons to evict, and re-measure canonicals.
+//   1. When connections are initially created there is more overhead in maxscale and at the server,
+//      which can (and does) lead to the wrong performance conclusions.
+//   2. Depending on the contents and number of rows in tables, different database engines
+//      have different performance advantages (InnoDb is always very fast for small tables).
+//
+// TODO make configurable, maybe.
+static std::array<maxbase::Duration, 4> eviction_schedules =
+{
+    std::chrono::minutes(2),
+    std::chrono::minutes(5),
+    std::chrono::minutes(10),
+    std::chrono::minutes(20)
+};
+
+// TODO need to add the default db to the key (or hash)
+
 PerformanceInfo SmartRouter::perf_find(const std::string& canonical)
 {
     std::unique_lock<std::mutex> guard(m_perf_mutex);
-    auto perf = m_performance.find(canonical);
 
-    if (perf.is_valid() && perf.age() > std::chrono::minutes(1))    // TODO to config, but not yet
+    auto perf_it = m_perfs.find(canonical);
+    if (perf_it != end(m_perfs) && !perf_it->second.is_updating())
     {
-        m_performance.remove(canonical);
+        if (perf_it->second.age() > eviction_schedules[perf_it->second.eviction_schedule()])
-        return PerformanceInfo();
+        {
+            MXS_SINFO("Trigger re-measure, schedule "
+                      << eviction_schedules[perf_it->second.eviction_schedule()]
+                      << ", perf: " << perf_it->second.host()
+                      << ", " << perf_it->second.duration() << ", "
+                      << show_some(canonical));
+
+            // Not actually evicting, but trigger a re-measure only for this caller (this worker).
+            perf_it->second.set_updating(true);
+            perf_it = end(m_perfs);
+        }
     }
 
-    return perf;
+    return perf_it != end(m_perfs) ? perf_it->second : PerformanceInfo();
 }
 
-bool SmartRouter::perf_update(const std::string& canonical, const PerformanceInfo& perf)
+void SmartRouter::perf_update(const std::string& canonical, const PerformanceInfo& perf)
 {
     std::unique_lock<std::mutex> guard(m_perf_mutex);
-    auto ret = m_performance.insert(canonical, perf);
 
-    if (ret)
+    auto perf_it = m_perfs.find(canonical);
+    if (perf_it != end(m_perfs))
     {
-        MXS_SDEBUG("Stored perf " << perf.duration() << ' ' << perf.host() << ' ' << show_some(canonical));
+        MXS_SINFO("Update perf: from "
-    }
+                  << perf_it->second.host() << ", " << perf_it->second.duration()
+                  << " to " << perf.host() << ", " << perf.duration()
+                  << ", " << show_some(canonical));
 
-    return ret;
+        size_t schedule = perf_it->second.eviction_schedule();
+        perf_it->second = perf;
+        perf_it->second.set_eviction_schedule(std::min(++schedule, eviction_schedules.size() - 1));
+        perf_it->second.set_updating(false);
+    }
+    else
+    {
+        m_perfs.insert({canonical, perf});
+        MXS_SDEBUG("Stored new perf: " << perf.host() << ", " << perf.duration()
+                                       << ", " << show_some(canonical));
+    }
 }

server/modules/routing/smartrouter/smartrouter.hh

@@ -26,7 +26,7 @@
 
 class SmartRouterSession;
 
-/** class Smartrouter. Only defines the mxs::Router<> functions needed for all routers.
+/** class Smartrouter. Contains and manages the performance info.
  */
 class SmartRouter : public mxs::Router<SmartRouter, SmartRouterSession>
 {
@@ -83,12 +83,15 @@ public:
 
     /** Thread safe update/insert a PerformanceInfo. Some entry expiration handling is done here.
      */
-    bool perf_update(const std::string& canonical, const PerformanceInfo& perf);
+    void perf_update(const std::string& canonical, const PerformanceInfo& perf);
 
 private:
     SmartRouter(SERVICE* service);
 
-    Config               m_config;
+    Config m_config;
-    CanonicalPerformance m_performance;
+
-    std::mutex           m_perf_mutex;
+    using Perfs = std::unordered_map<std::string, PerformanceInfo>;
+
+    std::mutex m_perf_mutex;
+    Perfs      m_perfs;
 };