MB-33151: Remove hifi mfu config param

2 bit LRU support was left as a dynamic config option to allow
easy testing and for customers to revert the eviction algorithm
changes if the hifi MFU changes caused issues. Hifi MFU has been
around long enough that we want to remove some complexity and get
rid of 2 bit LRU support. Remove the hifi_mfu config parameter
entirely and the 2 bit LRU code. The DcpProducer can still talk to
older nodes and send 2 bit LRU hotness values instead of hifi MFU
hotness values if the DcpConsumer does not hello with supports hifi
MFU.

Change-Id: Ibdbd39a070205911514d189eb00f2a8190e97373
Reviewed-on: http://review.couchbase.org/105338
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>
Reviewed-by: Daniel Owen <[email protected]>

Author: BenHuddleston

engines/ep/configuration.json

@@ -471,18 +471,6 @@
 	    "dynamic": true,
             "type": "size_t"
         },
-        "ht_eviction_policy": {
-            "default": "hifi_mfu",
-            "descr": "The eviction policy for the hash table",
-            "dynamic": true,
-            "type": "std::string",
-            "validator": {
-                "enum": [
-                    "2-bit_lru",
-                    "hifi_mfu"
-                ]
-            }
-        },
         "ht_locks": {
             "default": "47",
             "dynamic": true,

engines/ep/src/dcp/consumer.cc

@@ -180,8 +180,7 @@ DcpConsumer::DcpConsumer(EventuallyPersistentEngine& engine,
     pendingSetPriority = true;
     pendingEnableExtMetaData = true;
     pendingSupportCursorDropping = true;
-    pendingSupportHifiMFU =
-            (config.getHtEvictionPolicy() == "hifi_mfu");
+    pendingSupportHifiMFU = true;
     pendingEnableExpiryOpcode = true;
     syncReplNegotiation.state = SyncReplNegotiation::State::PendingRequest;
     // If a consumer_name was provided then tell the producer about it.

engines/ep/src/dcp/producer.cc

@@ -187,7 +187,6 @@ DcpProducer::DcpProducer(EventuallyPersistentEngine& e,
     setSupportAck(true);
     setReserved(true);
     pause(PausedReason::Initializing);
-
     if (notifyOnly) {
         setLogHeader("DCP (Notifier) " + getName() + " -");
     } else {
@@ -561,20 +560,16 @@ ENGINE_ERROR_CODE DcpProducer::streamRequest(
 }
 
 uint8_t DcpProducer::encodeItemHotness(const Item& item) const {
-    if (engine_.getConfiguration().getHtEvictionPolicy() == "hifi_mfu") {
-        auto freqCount = item.getFreqCounterValue();
-        if (consumerSupportsHifiMfu) {
-            // The consumer supports the hifi_mfu eviction
-            // policy, therefore use the frequency counter.
-            return freqCount;
-        }
-        // The consumer does not support the hifi_mfu
-        // eviction policy, therefore map from the 8-bit
-        // probabilistic counter (256 states) to NRU (4 states).
-        return ItemEviction::convertFreqCountToNRUValue(freqCount);
-    }
-    /* We are using the 2-bit_lru and therefore get the value */
-    return item.getNRUValue();
+    auto freqCount = item.getFreqCounterValue();
+    if (consumerSupportsHifiMfu) {
+        // The consumer supports the hifi_mfu eviction
+        // policy, therefore use the frequency counter.
+        return freqCount;
+    }
+    // The consumer does not support the hifi_mfu
+    // eviction policy, therefore map from the 8-bit
+    // probabilistic counter (256 states) to NRU (4 states).
+    return ItemEviction::convertFreqCountToNRUValue(freqCount);
 }
 
 ENGINE_ERROR_CODE DcpProducer::step(struct dcp_message_producers* producers) {

engines/ep/src/ep_engine.cc

@@ -550,8 +550,6 @@ cb::mcbp::Status EventuallyPersistentEngine::setFlushParam(
             getConfiguration().setPagerActiveVbPcnt(std::stoull(val));
         } else if (key == "pager_sleep_time_ms") {
             getConfiguration().setPagerSleepTimeMs(std::stoull(val));
-        } else if (key == "ht_eviction_policy") {
-            getConfiguration().setHtEvictionPolicy(val);
         } else if (key == "item_eviction_age_percentage") {
             getConfiguration().setItemEvictionAgePercentage(std::stoull(val));
         } else if (key == "item_eviction_freq_counter_age_threshold") {
@@ -4183,10 +4181,7 @@ ENGINE_ERROR_CODE EventuallyPersistentEngine::getStats(
     } else if (statKey == "dcp") {
         rv = doDcpStats(cookie, add_stat);
     } else if (statKey == "eviction") {
-        // Only return eviction stats if hifi_mfu eviction policy is used.
-        rv = (configuration.getHtEvictionPolicy() == "hifi_mfu")
-                     ? doEvictionStats(cookie, add_stat)
-                     : ENGINE_EINVAL;
+        rv = doEvictionStats(cookie, add_stat);
     } else if (statKey == "hash") {
         rv = doHashStats(cookie, add_stat);
     } else if (statKey == "vbucket") {

engines/ep/src/item_pager.cc

@@ -48,20 +48,18 @@ ItemPager::ItemPager(EventuallyPersistentEngine& e, EPStats& st)
       engine(e),
       stats(st),
       available(new std::atomic<bool>(true)),
-      phase(PAGING_UNREFERENCED),
+      phase(REPLICA_ONLY),
       doEvict(false),
       sleepTime(std::chrono::milliseconds(
               e.getConfiguration().getPagerSleepTimeMs())),
       notified(false) {
-    if (engine.getConfiguration().getHtEvictionPolicy() == "hifi_mfu") {
-        // For the hifi_mfu algorithm if a couchbase/persistent bucket we
-        // want to start visiting the replica vbucket first.  However for
-        // ephemeral we do not evict from replica vbuckets and therefore
-        // we start with active and pending vbuckets.
-        phase = (engine.getConfiguration().getBucketType() == "persistent")
-                        ? REPLICA_ONLY
-                        : ACTIVE_AND_PENDING_ONLY;
-    }
+    // For the hifi_mfu algorithm if a couchbase/persistent bucket we
+    // want to start visiting the replica vbucket first.  However for
+    // ephemeral we do not evict from replica vbuckets and therefore
+    // we start with active and pending vbuckets.
+    phase = (engine.getConfiguration().getBucketType() == "persistent")
+                    ? REPLICA_ONLY
+                    : ACTIVE_AND_PENDING_ONLY;
 }
 
 bool ItemPager::run(void) {
@@ -84,21 +82,6 @@ bool ItemPager::run(void) {
     double upper = static_cast<double>(stats.mem_high_wat);
     double lower = static_cast<double>(stats.mem_low_wat);
 
-    // If we dynamically switch from the hifi_mfu policy to the 2-bit_lru
-    // policy or vice-versa, we will not be in a valid phase.  Therefore
-    // reinitialise to the correct phase for the eviction policy.
-    if (engine.getConfiguration().getHtEvictionPolicy() == "hifi_mfu") {
-        if (phase != REPLICA_ONLY && phase != ACTIVE_AND_PENDING_ONLY) {
-            // Not a valid phase for the hifi_mfu policy, so reinitialise.
-            phase = (engine.getConfiguration().getBucketType() == "persistent")
-                            ? REPLICA_ONLY
-                            : ACTIVE_AND_PENDING_ONLY;
-        }
-    } else if (phase != PAGING_UNREFERENCED && phase != PAGING_RANDOM) {
-        // Not a valid phase for the 2-bit_lru policy, so reinitialise.
-        phase = PAGING_UNREFERENCED;
-    }
-
     if (current <= lower) {
         doEvict = false;
     }
@@ -126,33 +109,27 @@ bool ItemPager::run(void) {
         VBucketFilter filter;
         // For the hifi_mfu algorithm use the phase to filter which vbuckets
         // we want to visit (either replica or active/pending vbuckets).
-        if (cfg.getHtEvictionPolicy() == "hifi_mfu") {
-            vbucket_state_t state;
-            if (phase == REPLICA_ONLY) {
-                state = vbucket_state_replica;
-            } else if (phase == ACTIVE_AND_PENDING_ONLY) {
-                state = vbucket_state_active;
-                auto acceptableVBs = kvBucket->getVBucketsInState(state);
-                for (auto vb : acceptableVBs) {
-                    filter.addVBucket(vb);
-                }
-                state = vbucket_state_pending;
-            } else {
-                throw std::invalid_argument(
-                        "ItemPager::run - "
-                        "phase is invalid for hifi_mfu eviction algorithm");
-            }
+        vbucket_state_t state;
+        if (phase == REPLICA_ONLY) {
+            state = vbucket_state_replica;
+        } else if (phase == ACTIVE_AND_PENDING_ONLY) {
+            state = vbucket_state_active;
             auto acceptableVBs = kvBucket->getVBucketsInState(state);
             for (auto vb : acceptableVBs) {
                 filter.addVBucket(vb);
             }
+            state = vbucket_state_pending;
+        } else {
+            throw std::invalid_argument(
+                    "ItemPager::run - "
+                    "phase is invalid for hifi_mfu eviction algorithm");
+        }
+        auto acceptableVBs = kvBucket->getVBucketsInState(state);
+        for (auto vb : acceptableVBs) {
+            filter.addVBucket(vb);
         }
 
         bool isEphemeral = (cfg.getBucketType() == "ephemeral");
-        PagingVisitor::EvictionPolicy evictionPolicy =
-                (cfg.getHtEvictionPolicy() == "2-bit_lru")
-                        ? PagingVisitor::EvictionPolicy::lru2Bit
-                        : PagingVisitor::EvictionPolicy::hifi_mfu;
 
         auto pv = std::make_unique<PagingVisitor>(
                 *kvBucket,
@@ -166,8 +143,7 @@ bool ItemPager::run(void) {
                 &phase,
                 isEphemeral,
                 cfg.getItemEvictionAgePercentage(),
-                cfg.getItemEvictionFreqCounterAgeThreshold(),
-                evictionPolicy);
+                cfg.getItemEvictionFreqCounterAgeThreshold());
 
         // p99.99 is ~200ms
         const auto maxExpectedDurationForVisitorTask =
@@ -244,10 +220,6 @@ bool ExpiredItemPager::run(void) {
         Configuration& cfg = engine->getConfiguration();
         bool isEphemeral =
                 (engine->getConfiguration().getBucketType() == "ephemeral");
-        PagingVisitor::EvictionPolicy evictionPolicy =
-                (cfg.getHtEvictionPolicy() == "2-bit_lru")
-                        ? PagingVisitor::EvictionPolicy::lru2Bit
-                        : PagingVisitor::EvictionPolicy::hifi_mfu;
         auto pv = std::make_unique<PagingVisitor>(
                 *kvBucket,
                 stats,
@@ -260,8 +232,7 @@ bool ExpiredItemPager::run(void) {
                 /* pager_phase */ nullptr,
                 isEphemeral,
                 cfg.getItemEvictionAgePercentage(),
-                cfg.getItemEvictionFreqCounterAgeThreshold(),
-                evictionPolicy);
+                cfg.getItemEvictionFreqCounterAgeThreshold());
 
         // p99.99 is ~50ms (same as ItemPager).
         const auto maxExpectedDurationForVisitorTask =

engines/ep/src/item_pager.h

@@ -30,8 +30,6 @@ class EventuallyPersistentEngine;
  * The item pager phase
  */
 enum item_pager_phase {
-    PAGING_UNREFERENCED,
-    PAGING_RANDOM,
     REPLICA_ONLY, // Visit only replica vbuckets
     ACTIVE_AND_PENDING_ONLY // Visit only active and pending vbuckets
 };