SERVER-16469 findAndModify runImpl(): set limit of -1 on query

This allows findAndModify operations that include a sort to take
advantage of the top-K sort logic in the query engine.  This reduces
the memory footprint of the operation from O(N) to O(1), where N is
the number of documents matching the query predicate.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/mongo/db/commands/find_and_modify.cpp b/src/mongo/db/commands/find_and_modify.cpp
index 56410a59916..5467b7f705c 100644
--- a/src/mongo/db/commands/find_and_modify.cpp
+++ b/src/mongo/db/commands/find_and_modify.cpp
@@ -223,10 +223,15 @@ namespace mongo {
             bool found = false;
             {
                 CanonicalQuery* cq;
+                const BSONObj projection;
+                const long long skip = 0;
+                const long long limit = -1; // 1 document requested; negative indicates hard limit.
                 uassertStatusOK(CanonicalQuery::canonicalize(ns,
                                                              query,
                                                              sort,
-                                                             BSONObj(),  // projection
+                                                             projection,
+                                                             skip,
+                                                             limit,
                                                              &cq,
                                                              whereCallback));