SERVER-92904 Consider PBRT size when creating cursor response batch (…

…#29288) GitOrigin-RevId: 48d06e256241f5b4c1475b7c9b78be0ff9247523
mongodb · Nov 26, 2024 · dc1671f · dc1671f
1 parent fbbe8ea
commit dc1671f
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Showing 3 changed files with 23 additions and 3 deletions.
diff --git a/etc/backports_required_for_multiversion_tests.yml b/etc/backports_required_for_multiversion_tests.yml
@@ -557,6 +557,8 @@ last-continuous:
     ticket: SERVER-94635
   - test_file: jstests/core/query/project/projection_with_hashed_index.js
     ticket: SERVER-91757
+  - test_file: jstests/change_streams/report_post_batch_resume_token.js
+    ticket: SERVER-92904
   - test_file: jstests/core/ddl/create_indexes.js
     ticket: SERVER-90952
   - test_file: jstests/core/timeseries/timeseries_filter_extended_range.js
@@ -1170,6 +1172,8 @@ last-lts:
     ticket: SERVER-94635
   - test_file: jstests/core/query/project/projection_with_hashed_index.js
     ticket: SERVER-91757
+  - test_file: jstests/change_streams/report_post_batch_resume_token.js
+    ticket: SERVER-92904
   - test_file: jstests/core/ddl/create_indexes.js
     ticket: SERVER-90952
   - test_file: jstests/core/timeseries/timeseries_filter_extended_range.js

diff --git a/jstests/change_streams/report_post_batch_resume_token.js b/jstests/change_streams/report_post_batch_resume_token.js
@@ -224,4 +224,15 @@ assert.gt(bsonWoCompare(txnEvent3._id, previousGetMorePBRT), 0);
 // appear in the batch. Confirm that the postBatchResumeToken has been set correctly.
 getMorePBRT = csCursor.getResumeToken();
 assert.gte(bsonWoCompare(getMorePBRT, txnEvent3._id), 0);
+
+// Test that a batch does not exceed the limit (and throw BSONObjectTooLarge) with a large
+// post-batch resume token.
+csCursor = testCollection.watch();
+const kSecondDocSize = 80 * 1024;
+// Here, 4.5 is some "unlucky" (non-unique) weight to provoke an error.
+const kFirstDocSize = (16 * 1024 * 1024) - (4.5 * kSecondDocSize);
+testCollection.insertMany([{a: "x".repeat(kFirstDocSize)}, {_id: "x".repeat(kSecondDocSize)}]);
+assert.doesNotThrow(() => {
+    csCursor.hasNext();
+}, [], "Unexpected exception on 'csCursor.hasNext()'.");
 })();
diff --git a/src/mongo/db/commands/getmore_cmd.cpp b/src/mongo/db/commands/getmore_cmd.cpp
@@ -364,7 +364,7 @@ class GetMoreCmd final : public Command {
          * be returned by this getMore.
          *
          * Returns true if the cursor should be saved for subsequent getMores, and false otherwise.
-         * Fills out *numResults with the number of documents in the batch, which must be
+         * Fills out 'numResults' with the number of documents in the batch, which must be
          * initialized to zero by the caller.
          *
          * Throws an exception on failure.
@@ -387,9 +387,14 @@ class GetMoreCmd final : public Command {
             try {
                 while (!FindCommon::enoughForGetMore(batchSize, *numResults) &&
                        PlanExecutor::ADVANCED == (state = exec->getNext(&obj, nullptr))) {
+                    auto nextPostBatchResumeToken = exec->getPostBatchResumeToken();
+
                     // If adding this object will cause us to exceed the message size limit, then we
                     // stash it for later.
-                    if (!FindCommon::haveSpaceForNext(obj, *numResults, nextBatch->bytesUsed())) {
+                    if (!FindCommon::haveSpaceForNext(obj,
+                                                      *numResults,
+                                                      nextBatch->bytesUsed() +
+                                                          nextPostBatchResumeToken.objsize())) {
                         exec->stashResult(obj);
                         break;
                     }
@@ -398,7 +403,7 @@ class GetMoreCmd final : public Command {
                     awaitDataState(opCtx).shouldWaitForInserts = false;
 
                     // If this executor produces a postBatchResumeToken, add it to the response.
-                    nextBatch->setPostBatchResumeToken(exec->getPostBatchResumeToken());
+                    nextBatch->setPostBatchResumeToken(nextPostBatchResumeToken);
 
                     // At this point, we know that there will be at least one document in this
                     // batch. Reserve an initial estimated number of bytes for the response.