From ad45a5b1ad463c54d5196428d55b0080a53f19bc Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Sat, 17 Oct 2015 11:31:22 -0400
Subject: Database-server reconnection for MySQL

---
 src/c/urweb.c |  5 +++--
 src/mysql.sml | 28 +++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/src/c/urweb.c b/src/c/urweb.c
index 9371147b..d656ae03 100644
--- a/src/c/urweb.c
+++ b/src/c/urweb.c
@@ -813,7 +813,7 @@ static void uw_try_reconnecting(uw_context ctx) {
 
 void uw_try_reconnecting_and_restarting(uw_context ctx) {
   uw_try_reconnecting(ctx);
-  uw_error(ctx, UNLIMITED_RETRY, "Restarting transaction after fixing database connection");
+  uw_error(ctx, BOUNDED_RETRY, "Restarting transaction after fixing database connection");
 }
 
 void uw_ensure_transaction(uw_context ctx) {
@@ -826,7 +826,8 @@ void uw_ensure_transaction(uw_context ctx) {
     }
 
     ctx->transaction_started = 1;
-  }
+  } else if (ctx->at_most_one_query && !ctx->db)
+    uw_try_reconnecting(ctx);
 }
 
 uw_Basis_client uw_Basis_self(uw_context ctx) {
diff --git a/src/mysql.sml b/src/mysql.sml
index 057d73ff..692be0a2 100644
--- a/src/mysql.sml
+++ b/src/mysql.sml
@@ -861,11 +861,17 @@ fun queryCommon {loc, query, cols, doCols} =
                                           end) cols,
          newline,
 
-         string "if (mysql_stmt_reset(stmt)) uw_error(ctx, FATAL, \"",
-         string (ErrorMsg.spanToString loc),
-         string ": Error reseting statement: %s\\n%s\", ",
-         query,
-         string ", mysql_error(conn->conn));",
+         string "if (mysql_stmt_reset(stmt)) {",
+         box [newline,
+              string "if (mysql_errno(conn->conn) == 2006) uw_try_reconnecting_and_restarting(ctx);",
+              newline,
+              string "uw_error(ctx, FATAL, \"",
+              string (ErrorMsg.spanToString loc),
+              string ": Error reseting statement: %s\\n%s\", ",
+              query,
+              string ", mysql_error(conn->conn));",
+              newline],
+         string "}",
          newline,
          newline,
 
@@ -1233,7 +1239,9 @@ fun queryPrepared {loc, id, query, inputs, cols, doCols, nested} =
 
 fun dmlCommon {loc, dml, mode} =
     box [string "if (mysql_stmt_execute(stmt)) {",
-         box [string "if (mysql_errno(conn->conn) == 1213)",
+         box [string "if (mysql_errno(conn->conn) == 2006) uw_try_reconnecting_and_restarting(ctx);",
+              newline,
+              string "if (mysql_errno(conn->conn) == 1213)",
               newline,
               box [string "uw_error(ctx, UNLIMITED_RETRY, \"Deadlock detected\");",
                    newline],
@@ -1540,7 +1548,13 @@ fun nextval {loc, seqE, seqName} =
          newline,
          newline,
 
-         string "if (mysql_query(conn->conn, insert)) uw_error(ctx, FATAL, \"'nextval' INSERT failed\");",
+         string "if (mysql_query(conn->conn, insert)) {",
+         box [newline,
+              string "if (mysql_errno(conn->conn) == 2006) uw_try_reconnecting_and_restarting(ctx);",
+              newline,
+              string "uw_error(ctx, FATAL, \"'nextval' INSERT failed\");",
+              newline],
+         string "}",
          newline,
          string "n = mysql_insert_id(conn->conn);",
          newline,
-- 
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