SERVER-78314 Add server parameter internalQueryDocumentSourceWriterBatchExtraReservedBytesr4.4.23-rc0r4.4.23

(cherry picked from commit 67d3e420aa2c7e693fac97318a4a3fec1c6ced80)

2 files changed, 17 insertions, 15 deletions

diff --git a/src/mongo/db/pipeline/document_source_writer.h b/src/mongo/db/pipeline/document_source_writer.h
index 10bb21ddefc..6b845745c18 100644
--- a/src/mongo/db/pipeline/document_source_writer.h
+++ b/src/mongo/db/pipeline/document_source_writer.h
@@ -237,19 +237,20 @@ DocumentSource::GetNextResult DocumentSourceWriter<B>::doGetNext() {
             _initialized = true;
         }
 
-        // While most metadata attached to a command is limited to less than a KB,
-        // Impersonation metadata may grow to an arbitrary size.
-        // Ask the active Client how much impersonation metadata we'll use for it,
-        // add in our own estimate of write header size, and assume that the rest can fit
-        // in the space reserved by BSONObjMaxUserSize's overhead plus
-        // the value from the server parameter: documentSourceWriterBatchBuffer.
+        // While most metadata attached to a command is limited to less than a KB, Impersonation
+        // metadata may grow to an arbitrary size.
+        //
+        // Ask the active Client how much impersonation metadata we'll use for it, add in our own
+        // estimate of write header size, and assume that the rest can fit in the space reserved by
+        // BSONObjMaxUserSize's overhead plus the value from the server parameter:
+        // internalQueryDocumentSourceWriterBatchExtraReservedBytes.
         const auto estimatedMetadataSizeBytes =
-            rpc::estimateImpersonatedUserMetadataSize(pExpCtx->opCtx) +
-            gDocumentSourceWriterBatchBufferBytes;
+            rpc::estimateImpersonatedUserMetadataSize(pExpCtx->opCtx);
 
         BatchedCommandRequest batchWrite = initializeBatchedWriteRequest();
         const auto writeHeaderSize = estimateWriteHeaderSize(batchWrite);
-        const auto initialRequestSize = estimatedMetadataSizeBytes + writeHeaderSize;
+        const auto initialRequestSize = estimatedMetadataSizeBytes + writeHeaderSize +
+            internalQueryDocumentSourceWriterBatchExtraReservedBytes.load();
 
         uassert(7637800,
                 "Unable to proceed with write while metadata size ({}KB) exceeds {}KB"_format(
diff --git a/src/mongo/db/query/query_knobs.idl b/src/mongo/db/query/query_knobs.idl
index 53885816fc8..7dc4684eb80 100644
--- a/src/mongo/db/query/query_knobs.idl
+++ b/src/mongo/db/query/query_knobs.idl
@@ -448,12 +448,13 @@ server_parameters:
     cpp_vartype: AtomicWord<bool>
     default: false
 
-  documentSourceWriterBatchBuffer:
-    description: 'Space to reserve in document source writer batches for miscellaneous metadata'
-    set_at: startup
-    cpp_vartype: int
-    cpp_varname: gDocumentSourceWriterBatchBufferBytes
+  internalQueryDocumentSourceWriterBatchExtraReservedBytes:
+    description: "Space to reserve in document source writer batches for miscellaneous metadata"
+    set_at: [ startup, runtime ]
+    cpp_vartype: AtomicWord<int>
+    cpp_varname: internalQueryDocumentSourceWriterBatchExtraReservedBytes
     validator:
       gte: 0
-      lte: 8388608 # 8MB
+      lte: 
+        expr: 8 * 1024 * 1024 # 8MB
     default: 0