Enforce a max connection timeout

Summary:
Enforce a maximum connection timeout without impacting pooled
operations.

This allows pooled conns to set the connect timeout and
influence how long to remain queued for available conns,
while not choking up the thread with connects that are
unlikely to succeed.

Add a GFLAG as a backdoor for those who insist on doing it
the wrong way

Reviewed By: jupyung

Differential Revision: D45589828

fbshipit-source-id: 3d4642daa530848ea8ff75d822b8b7b6251a195b

squangle/mysql_client/Operation.cpp

@@ -36,6 +36,15 @@ DEFINE_int64(
     10 * 1000 * 1000,
     "default timeout, in micros, for mysql operations");
 
+DEFINE_int64(
+    async_mysql_max_connect_timeout_micros,
+#if defined(FOLLY_SANITIZE_ADDRESS) || (FOLLY_SANITIZE_THREAD)
+    30 * 1000 * 1000,
+#else
+    3 * 1000 * 1000,
+#endif
+    "The maximum connect timeout, to protect customers from themselves");
+
 namespace facebook {
 namespace common {
 namespace mysql_client {
@@ -218,6 +227,10 @@ Operation* Operation::run() {
         state() == OperationState::Unstarted, db::OperationStateException);
     state_ = OperationState::Pending;
   }
+  if (getOperationType() == db::OperationType::Connect) {
+    timeout_ = std::min(
+        Duration(FLAGS_async_mysql_max_connect_timeout_micros), timeout_);
+  }
   return specializedRun();
 }
 

squangle/mysql_client/Operation.h

@@ -64,6 +64,7 @@
 #include "squangle/mysql_client/Query.h"
 #include "squangle/mysql_client/Row.h"
 
+DECLARE_int64(async_mysql_max_connect_timeout_micros);
 namespace facebook {
 namespace common {
 namespace mysql_client {