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

(cherry picked from commit bfc606f1cc5ad931f054b5c152993a57d30eef64)

2 files changed, 18 insertions, 1 deletions

diff --git a/jstests/noPassthrough/serverstatus_indexbulkbuilder.js b/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
index 044558a5b27..5c7859149b0 100644
--- a/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
+++ b/jstests/noPassthrough/serverstatus_indexbulkbuilder.js
@@ -14,6 +14,7 @@ load('jstests/noPassthrough/libs/index_build.js');
 
 const replSet = new ReplSetTest({
     nodes: 1,
+    nodeOptions: {setParameter: {maxIndexBuildMemoryUsageMegabytes: 50}},
 });
 replSet.startSet();
 replSet.initiate();
@@ -25,7 +26,7 @@ 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),
     }));
 }
 
@@ -38,6 +39,8 @@ assert(serverStatus.hasOwnProperty('indexBulkBuilder'),
 let indexBulkBuilderSection = serverStatus.indexBulkBuilder;
 assert.eq(indexBulkBuilderSection.count, 1, tojson(indexBulkBuilderSection));
 assert.eq(indexBulkBuilderSection.resumed, 0, tojson(indexBulkBuilderSection));
+assert.eq(indexBulkBuilderSection.filesOpenedForExternalSort, 1, tojson(indexBulkBuilderSection));
+assert.eq(indexBulkBuilderSection.filesClosedForExternalSort, 1, tojson(indexBulkBuilderSection));
 
 // Shut down server during an index to verify 'resumable' value on restart.
 IndexBuildTest.pauseIndexBuilds(primary);
@@ -60,6 +63,11 @@ ResumableIndexBuildTest.assertCompleted(primary, coll, [buildUUID], ['a_1', 'b_1
 indexBulkBuilderSection = testDB.serverStatus().indexBulkBuilder;
 assert.eq(indexBulkBuilderSection.count, 1, tojson(indexBulkBuilderSection));
 assert.eq(indexBulkBuilderSection.resumed, 1, tojson(indexBulkBuilderSection));
+// Even though the amount of index data for b_1 is well under the configured memory usage limit,
+// the resumable index build logic dictates that we spill the sorter data to disk on shutdown
+// and read it back on startup.
+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 563c799251d..63148efb8cf 100644
--- a/src/mongo/db/index/index_access_method.cpp
+++ b/src/mongo/db/index/index_access_method.cpp
@@ -97,6 +97,8 @@ public:
         BSONObjBuilder builder;
         builder.append("count", count.loadRelaxed());
         builder.append("resumed", resumed.loadRelaxed());
+        builder.append("filesOpenedForExternalSort", sorterFileStats.opened.loadRelaxed());
+        builder.append("filesClosedForExternalSort", sorterFileStats.closed.loadRelaxed());
         return builder.obj();
     }
 
@@ -106,6 +108,12 @@ public:
     // Number of times the bulk builder was created for a resumable index build.
     // This value should not exceed 'count'.
     AtomicWord<long long> resumed;
+
+    // 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;
 
 /**
@@ -124,6 +132,7 @@ SortOptions makeSortOptions(size_t maxMemoryUsageBytes, StringData dbName) {
         .TempDir(storageGlobalParams.dbpath + "/_tmp")
         .ExtSortAllowed()
         .MaxMemoryUsageBytes(maxMemoryUsageBytes)
+        .FileStats(&indexBulkBuilderSSS.sorterFileStats)
         .DBName(dbName.toString());
 }