SERVER-6565 Do not use primary if secondaries are available for slaveOk

3 files changed, 13 insertions, 3 deletions

diff --git a/src/mongo/client/dbclient_rs.cpp b/src/mongo/client/dbclient_rs.cpp
index 8df431a89eb..4f3853e4161 100644
--- a/src/mongo/client/dbclient_rs.cpp
+++ b/src/mongo/client/dbclient_rs.cpp
@@ -1192,7 +1192,12 @@ namespace mongo {
             return false;
         }
 
-        if (readPreference == ReadPreference_SecondaryOnly &&
+        if ((readPreference == ReadPreference_SecondaryOnly ||
+                /* This is the original behavior for slaveOk. This can result to reading
+                 * data back in time, but the main idea here is to avoid overloading the
+                 * primary when secondary is available.
+                 */
+                readPreference == ReadPreference_SecondaryPreferred) &&
                 !okForSecondaryQueries()) {
             return false;
         }
diff --git a/src/mongo/client/dbclient_rs.h b/src/mongo/client/dbclient_rs.h
index 9cda552a1e2..98d27fc9944 100644
--- a/src/mongo/client/dbclient_rs.h
+++ b/src/mongo/client/dbclient_rs.h
@@ -99,6 +99,11 @@ namespace mongo {
             }
 
             /**
+             * Checks whether this nodes is compatible with the given readPreference and
+             * tag. Compatibility check is strict in the sense that secondary preferred
+             * is treated like secondary only and primary preferred is treated like
+             * primary only.
+             *
              * @return true if this node is compatible with the read preference and tags.
              */
             bool isCompatible(ReadPreference readPreference, const TagSet* tag) const;
diff --git a/src/mongo/dbtests/replica_set_monitor_test.cpp b/src/mongo/dbtests/replica_set_monitor_test.cpp
index 771ee60c0f7..b2a7377c068 100644
--- a/src/mongo/dbtests/replica_set_monitor_test.cpp
+++ b/src/mongo/dbtests/replica_set_monitor_test.cpp
@@ -199,7 +199,7 @@ namespace {
 
             ASSERT( node.isCompatible( ReadPreference_PrimaryOnly, &tags ));
             ASSERT( node.isCompatible( ReadPreference_PrimaryPreferred, &tags ));
-            ASSERT( node.isCompatible( ReadPreference_SecondaryPreferred, &tags ));
+            ASSERT( !node.isCompatible( ReadPreference_SecondaryPreferred, &tags ));
             ASSERT( !node.isCompatible( ReadPreference_SecondaryOnly, &tags ));
             ASSERT( node.isCompatible( ReadPreference_Nearest, &tags ));
         }
@@ -292,7 +292,7 @@ namespace {
 
             ASSERT( node.isCompatible( ReadPreference_PrimaryOnly, &tags ));
             ASSERT( node.isCompatible( ReadPreference_PrimaryPreferred, &tags ));
-            ASSERT( node.isCompatible( ReadPreference_SecondaryPreferred, &tags ));
+            ASSERT( !node.isCompatible( ReadPreference_SecondaryPreferred, &tags ));
             ASSERT( !node.isCompatible( ReadPreference_SecondaryOnly, &tags ));
             ASSERT( node.isCompatible( ReadPreference_Nearest, &tags ));
         }