SERVER-4786 Allow specifying sample rate of slow queries

Adds a sampleRate parameter to the profile command, a value
on the interval [0, 1] which indicates which fraction of
operations should be randomly sampled for profiling and
logging. This allows users to reduce their slowms threshold
or increase their profiling level with less performance
impact on the system.

Closes #1099

Signed-off-by: David Storch <david.storch@10gen.com>

2 files changed, 27 insertions, 0 deletions

diff --git a/src/mongo/bson/util/bson_extract.cpp b/src/mongo/bson/util/bson_extract.cpp
index 84c9cc92de6..8a453c02472 100644
--- a/src/mongo/bson/util/bson_extract.cpp
+++ b/src/mongo/bson/util/bson_extract.cpp
@@ -185,6 +185,18 @@ Status bsonExtractDoubleField(const BSONObj& object, StringData fieldName, doubl
     return Status::OK();
 }
 
+Status bsonExtractDoubleFieldWithDefault(const BSONObj& object,
+                                         StringData fieldName,
+                                         double defaultValue,
+                                         double* out) {
+    Status status = bsonExtractDoubleField(object, fieldName, out);
+    if (status == ErrorCodes::NoSuchKey) {
+        *out = defaultValue;
+        status = Status::OK();
+    }
+    return status;
+}
+
 Status bsonExtractIntegerFieldWithDefault(const BSONObj& object,
                                           StringData fieldName,
                                           long long defaultValue,
diff --git a/src/mongo/bson/util/bson_extract.h b/src/mongo/bson/util/bson_extract.h
index cedc84cd01f..a4e2b90d82d 100644
--- a/src/mongo/bson/util/bson_extract.h
+++ b/src/mongo/bson/util/bson_extract.h
@@ -158,6 +158,21 @@ Status bsonExtractIntegerFieldWithDefault(const BSONObj& object,
                                           long long* out);
 
 /**
+ * Finds a double-precision floating point element named "fieldName" in "object".
+ *
+ * If a field named "fieldName" is present, and is a double, stores the value of the field into
+ * "*out". If no field named fieldName is present, sets "*out" to "defaultValue". In these cases,
+ * returns Status::OK().
+ *
+ * If "fieldName" is present more than once, behavior is undefined. If the found field is not a
+ * double, returns ErrorCodes::TypeMismatch.
+ */
+Status bsonExtractDoubleFieldWithDefault(const BSONObj& object,
+                                         StringData fieldName,
+                                         double defaultValue,
+                                         double* out);
+
+/**
  * Finds a std::string element named "fieldName" in "object".
  *
  * If a field named "fieldName" is present, and is a string, stores the value of the field into