SERVER-65024 Fix the uniqueness constraint handling for foreground index builds

(cherry picked from commit 5985d757ddc2645fb1b5df88f78abf6b9a833452)

3 files changed, 9 insertions, 9 deletions

diff --git a/src/mongo/db/catalog/index_catalog.h b/src/mongo/db/catalog/index_catalog.h
index 2f922b0bcc3..93480e3a0b6 100644
--- a/src/mongo/db/catalog/index_catalog.h
+++ b/src/mongo/db/catalog/index_catalog.h
@@ -76,7 +76,7 @@ enum class IndexBuildMethod {
      */
     kHybrid,
     /**
-     * Perform a collection scan to dump all keys into the exteral sorter, then into the index.
+     * Perform a collection scan to dump all keys into the external sorter, then into the index.
      * During this process, callers guarantee that no writes will be accepted on this collection.
      */
     kForeground,
diff --git a/src/mongo/db/catalog/multi_index_block.cpp b/src/mongo/db/catalog/multi_index_block.cpp
index 1ad98278b22..47fe26aa513 100644
--- a/src/mongo/db/catalog/multi_index_block.cpp
+++ b/src/mongo/db/catalog/multi_index_block.cpp
@@ -324,10 +324,13 @@ StatusWith<std::vector<BSONObj>> MultiIndexBlock::init(
             collection->getIndexCatalog()->prepareInsertDeleteOptions(
                 opCtx, collection->ns(), descriptor, &index.options);
 
-            // Index builds always relax constraints and check for violations at commit-time.
+            // Foreground index builds have to check for duplicates. Other index builds can relax
+            // constraints and check for violations at commit-time.
             index.options.getKeysMode =
                 InsertDeleteOptions::ConstraintEnforcementMode::kRelaxConstraints;
-            index.options.dupsAllowed = true;
+            index.options.dupsAllowed = _method == IndexBuildMethod::kForeground
+                ? !descriptor->unique() || _ignoreUnique
+                : true;
             index.options.fromIndexBuilder = true;
 
             LOGV2(20384,
diff --git a/src/mongo/db/catalog/multi_index_block.h b/src/mongo/db/catalog/multi_index_block.h
index fa747afd8a3..840770595cf 100644
--- a/src/mongo/db/catalog/multi_index_block.h
+++ b/src/mongo/db/catalog/multi_index_block.h
@@ -82,12 +82,9 @@ public:
     ~MultiIndexBlock();
 
     /**
-     * By default we enforce the 'unique' flag in specs when building an index by failing.
-     * If this is called before init(), we will ignore unique violations. This has no effect if
-     * no specs are unique.
-     *
-     * If this is called, any 'dupRecords' set passed to dumpInsertsFromBulk() will never be
-     * filled.
+     * When this is called:
+     * For hybrid index builds, the index interceptor will not track duplicates.
+     * For foreground index builds, the uniqueness constraint will be relaxed.
      */
     void ignoreUniqueConstraint();