MB-33768: Add stat for num of items expelled from checkpoints

Adds the stat ep_items_expelled_from_checkpoints, which records the
total number of items (including meta items) that have been expelled
from checkpoints.

It copies a similar format to the ep_items_rm_from_checkpoints, which
tracks to the total number of items removed from checkpoints.

Change-Id: I673d4ef35c3c33b8013342886d8807c91a7f3cff
Reviewed-on: http://review.couchbase.org/107713
Reviewed-by: Jim Walker <[email protected]>
Tested-by: Build Bot <[email protected]>

Author: owend74

engines/ep/docs/stats.org

@@ -160,6 +160,11 @@ For introductory information on stats within Couchbase, start with the
 | ep_expiry_pager_task_time             | Time of the next expiry pager task      |
 |                                       | (GMT), NOT_SCHEDULED if expiry pager    |
 |                                       | has been disabled                       |
+| ep_items_expelled_from_checkpoints    | Number of items expelled from           |
+|                                       | checkpoints. Expelled refers to items   |
+|                                       | that have been ejected from memory      |
+|                                       | but are still considered to be part of  |
+|                                       | the checkpoint.                         |
 | ep_items_rm_from_checkpoints          | Number of items removed from closed     |
 |                                       | unreferenced checkpoints                |
 | ep_num_value_ejects                   | Number of times item values got         |
@@ -1250,6 +1255,7 @@ Reset Stats:
 | ep_io_num_write                                |
 | ep_io_bg_fetch_doc_bytes                       |
 | ep_io_write_bytes                              |
+| ep_items_expelled_from_checkpoints             |
 | ep_items_rm_from_checkpoints                   |
 | ep_num_eject_failures                          |
 | ep_num_pager_runs                              |

engines/ep/src/checkpoint_manager.cc

@@ -565,6 +565,8 @@ size_t CheckpointManager::expelUnreferencedCheckpointItems() {
         expelledItems = currentCheckpoint->expelItems(expelUpToAndIncluding);
     }
 
+    stats.itemsExpelledFromCheckpoints.fetch_add(expelledItems.size());
+
     /*
      * We are now outside of the queueLock when the method exits,
      * expelledItems will go out of scope and so the reference count

engines/ep/src/ep_engine.cc

@@ -2702,6 +2702,9 @@ ENGINE_ERROR_CODE EventuallyPersistentEngine::doEngineStats(
                     epstats.freqDecayerRuns,
                     add_stat,
                     cookie);
+    add_casted_stat("ep_items_expelled_from_checkpoints",
+                    epstats.itemsExpelledFromCheckpoints,
+                    add_stat, cookie);
     add_casted_stat("ep_items_rm_from_checkpoints",
                     epstats.itemsRemovedFromCheckpoints,
                     add_stat, cookie);

engines/ep/src/stats.cc

@@ -66,6 +66,7 @@ EPStats::EPStats()
       pagerRuns(0),
       expiryPagerRuns(0),
       freqDecayerRuns(0),
+      itemsExpelledFromCheckpoints(0),
       itemsRemovedFromCheckpoints(0),
       numValueEjects(0),
       numFailedEjects(0),

engines/ep/src/stats.h

@@ -230,6 +230,8 @@ class EPStats {
     Counter expiryPagerRuns;
     //! Number of times the item frequency decayer runs
     Counter freqDecayerRuns;
+    //! The number items expelled from checkpoints
+    Counter itemsExpelledFromCheckpoints;
     //! Number of items removed from closed unreferenced checkpoints.
     Counter itemsRemovedFromCheckpoints;
     //! Number of times a value is ejected
@@ -505,6 +507,7 @@ class EPStats {
         pagerRuns.store(0);
         expiryPagerRuns.store(0);
         freqDecayerRuns.store(0);
+        itemsExpelledFromCheckpoints.store(0);
         itemsRemovedFromCheckpoints.store(0);
         numValueEjects.store(0);
         numFailedEjects.store(0);

engines/ep/tests/ep_testsuite.cc

@@ -6959,6 +6959,7 @@ static enum test_result test_mb19687_fixed(EngineIface* h) {
               "ep_item_freq_decayer_percent",
               "ep_item_num",
               "ep_item_num_based_new_chk",
+              "ep_items_expelled_from_checkpoints",
               "ep_items_rm_from_checkpoints",
               "ep_keep_closed_chks",
               "ep_kv_size",

engines/ep/tests/module_tests/checkpoint_test.cc

@@ -1699,6 +1699,7 @@ TYPED_TEST(CheckpointTest, expelCheckpointItemsTest) {
      */
 
     EXPECT_EQ(itemCount + 1, this->manager->expelUnreferencedCheckpointItems());
+    EXPECT_EQ(itemCount + 1, this->global_stats.itemsExpelledFromCheckpoints);
 
     /*
      * After expelling checkpoint now looks as follows:
@@ -1760,6 +1761,7 @@ TYPED_TEST(CheckpointTest, expelCheckpointItemsWithDuplicateTest) {
     }
 
     ASSERT_EQ(itemCount + 1, this->manager->expelUnreferencedCheckpointItems());
+    EXPECT_EQ(itemCount + 1, this->global_stats.itemsExpelledFromCheckpoints);
 
     /*
      * After expelling checkpoint now looks as follows:
@@ -1812,6 +1814,7 @@ TYPED_TEST(CheckpointTest, expelCursorPointingToLastItem) {
      */
 
     EXPECT_EQ(itemCount + 1 , this->manager->expelUnreferencedCheckpointItems());
+    EXPECT_EQ(itemCount + 1, this->global_stats.itemsExpelledFromCheckpoints);
 
     /*
      * After expelling checkpoint now looks as follows:
@@ -1841,6 +1844,7 @@ TYPED_TEST(CheckpointTest, expelCursorPointingToChkptStart) {
      */
 
     EXPECT_EQ(0 , this->manager->expelUnreferencedCheckpointItems());
+    EXPECT_EQ(0, this->global_stats.itemsExpelledFromCheckpoints);
 }
 
 // Test that if we want to evict items from seqno X, but have a meta-data item
@@ -1889,4 +1893,5 @@ TYPED_TEST(CheckpointTest, dontExpelIfCursorAtMetadataItemWithSameSeqno) {
 
     // We should not expel any items due to dcpCursor1
     EXPECT_EQ(0, this->manager->expelUnreferencedCheckpointItems());
+    EXPECT_EQ(0, this->global_stats.itemsExpelledFromCheckpoints);
 }