SERVER-64659 add external sorter file handle metrics to indexBulkBuilder server status section

(cherry picked from commit bfc606f1cc5ad931f054b5c152993a57d30eef64)

2 files changed, 14 insertions, 2 deletions

diff --git a/jstests/noPassthrough/serverstatus_indexbulkbuilder.js b/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
index 780033e4e62..a7b6bdbec3f 100644
--- a/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
+++ b/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
@@ -12,6 +12,7 @@
 
 const replSet = new ReplSetTest({
     nodes: 1,
+    nodeOptions: {setParameter: {maxIndexBuildMemoryUsageMegabytes: 50}},
 });
 replSet.startSet();
 replSet.initiate();
@@ -23,7 +24,7 @@ let coll = testDB.getCollection('t');
 for (let i = 0; i < 10; i++) {
     assert.commandWorked(coll.insert({
         _id: i,
-        a: i,
+        a: 'a'.repeat(10 * 1024 * 1024),
     }));
 }
 
@@ -35,6 +36,8 @@ assert(serverStatus.hasOwnProperty('indexBulkBuilder'),
 
 let indexBulkBuilderSection = serverStatus.indexBulkBuilder;
 assert.eq(indexBulkBuilderSection.count, 1, tojson(indexBulkBuilderSection));
+assert.eq(indexBulkBuilderSection.filesOpenedForExternalSort, 1, tojson(indexBulkBuilderSection));
+assert.eq(indexBulkBuilderSection.filesClosedForExternalSort, 1, tojson(indexBulkBuilderSection));
 
 replSet.stopSet();
 })();
diff --git a/src/mongo/db/index/index_access_method.cpp b/src/mongo/db/index/index_access_method.cpp
index 67b09f80563..cd098ab11d5 100644
--- a/src/mongo/db/index/index_access_method.cpp
+++ b/src/mongo/db/index/index_access_method.cpp
@@ -99,11 +99,19 @@ public:
     BSONObj generateSection(OperationContext* opCtx, const BSONElement& configElement) const final {
         BSONObjBuilder builder;
         builder.append("count", count.loadRelaxed());
+        builder.append("filesOpenedForExternalSort", sorterFileStats.opened.loadRelaxed());
+        builder.append("filesClosedForExternalSort", sorterFileStats.closed.loadRelaxed());
         return builder.obj();
     }
 
     // Number of instances of the bulk builder created.
     AtomicWord<long long> count;
+
+    // Number of times the external sorter opened/closed a file handle to spill data to disk.
+    // This pair of counters in aggregate indicate the number of open file handles used by
+    // the external sorter and may be useful in diagnosing situations where the process is
+    // close to exhausting this finite resource.
+    SorterFileStats sorterFileStats;
 } indexBulkBuilderSSS;
 
 /**
@@ -562,7 +570,8 @@ AbstractIndexAccessMethod::BulkBuilderImpl::BulkBuilderImpl(IndexCatalogEntry* i
           SortOptions()
               .TempDir(storageGlobalParams.dbpath + "/_tmp")
               .ExtSortAllowed()
-              .MaxMemoryUsageBytes(maxMemoryUsageBytes),
+              .MaxMemoryUsageBytes(maxMemoryUsageBytes)
+              .FileStats(&indexBulkBuilderSSS.sorterFileStats),
           BtreeExternalSortComparison(),
           std::pair<KeyString::Value::SorterDeserializeSettings,
                     mongo::NullValue::SorterDeserializeSettings>(