SERVER-61185 Use WT prefix_key search for unique index lookups

2 files changed, 11 insertions, 7 deletions

diff --git a/jstests/noPassthrough/profile_operation_metrics.js b/jstests/noPassthrough/profile_operation_metrics.js
index c8ba22c52cb..a41f36227c0 100644
--- a/jstests/noPassthrough/profile_operation_metrics.js
+++ b/jstests/noPassthrough/profile_operation_metrics.js
@@ -683,10 +683,9 @@ const operations = [
         },
         profileFilter: {op: 'insert', 'command.insert': collName},
         profileAssert: (db, profileDoc) => {
-            // Insert should not perform any reads.
             assert.eq(profileDoc.docBytesRead, 0);
             assert.eq(profileDoc.docUnitsRead, 0);
-            // Reads the index entry for 'a' to determine uniqueness.
+            // The insert will perform a read to ensure uniqueness of 'a'.
             assert.eq(profileDoc.idxEntryBytesRead, 6);
             assert.eq(profileDoc.idxEntryUnitsRead, 1);
             assert.eq(profileDoc.cursorSeeks, 1);
@@ -794,7 +793,7 @@ const operations = [
                 assert.gte(profileDoc.docUnitsRead, 9);
                 assert.gte(profileDoc.cursorSeeks, 4);
             }
-            // Reads index entries on '_id' for the lookup and 'a' to ensure uniqueness.
+            // Reads index entries on '_id' and 'a' to ensure uniqueness.
             assert.eq(profileDoc.idxEntryBytesRead, 10);
             assert.eq(profileDoc.idxEntryUnitsRead, 2);
             if (FixtureHelpers.isReplSet(db)) {
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
index d3da10b5d3c..78ef755ffb7 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_index.cpp
@@ -1407,13 +1407,13 @@ bool WiredTigerIndexUnique::_keyExists(OperationContext* opCtx,
     int cmp;
     int ret = wiredTigerPrepareConflictRetry(opCtx, [&] { return c->search_near(c, &cmp); });
 
+    auto& metricsCollector = ResourceConsumption::MetricsCollector::get(opCtx);
+    metricsCollector.incrementOneCursorSeek();
+
     if (ret == WT_NOTFOUND)
         return false;
     invariantWTOK(ret);
 
-    auto& metricsCollector = ResourceConsumption::MetricsCollector::get(opCtx);
-    metricsCollector.incrementOneCursorSeek();
-
     if (cmp == 0)
         return true;
 
@@ -1574,7 +1574,12 @@ StatusWith<bool> WiredTigerIndexUnique::_insert(OperationContext* opCtx,
             fmt::format("WiredTigerIndexUnique::_insert: remove: {}; uri: {}", _indexName, _uri));
 
         // Second phase looks up for existence of key to avoid insertion of duplicate key
-        if (_keyExists(opCtx, c, keyString.getBuffer(), sizeWithoutRecordId)) {
+        // The usage of 'prefix_key=true' enables an optimization that allows this search to return
+        // more quickly. See SERVER-56509.
+        c->reconfigure(c, "prefix_key=true");
+        ON_BLOCK_EXIT([c] { c->reconfigure(c, "prefix_key=false"); });
+        auto keyExists = _keyExists(opCtx, c, keyString.getBuffer(), sizeWithoutRecordId);
+        if (keyExists) {
             auto key = KeyString::toBson(
                 keyString.getBuffer(), sizeWithoutRecordId, _ordering, keyString.getTypeBits());
             auto entry = _desc->getEntry();