database/sql: Retry with a fresh connection after maxBadConnRetries

Previously if the connection pool was larger than maxBadConnRetries
and there were a lot of bad connections in the pool (for example if
the database server was restarted), a query might have failed with an
ErrBadConn unnecessarily.  Instead of trying to guess how many times
to retry, try maxBadConnRetries times and then force a fresh
connection to be used for the last attempt.  At the same time, lower
maxBadConnRetries to a smaller value now that it's not that important
to retry so many times from the free connection list.

Fixes #8834

Change-Id: I6542f151a766a658980fb396fa4880ecf5874e3d
Reviewed-on: https://go-review.googlesource.com/2034
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 14 insertions, 9 deletions

diff --git a/src/database/sql/fakedb_test.go b/src/database/sql/fakedb_test.go
index a993fd46ed..8cbbb29a7c 100644
--- a/src/database/sql/fakedb_test.go
+++ b/src/database/sql/fakedb_test.go
@@ -89,7 +89,10 @@ type fakeConn struct {
 	stmtsMade   int
 	stmtsClosed int
 	numPrepare  int
-	bad         bool
+
+	// bad connection tests; see isBad()
+	bad       bool
+	stickyBad bool
 }
 
 func (c *fakeConn) incrStat(v *int) {
@@ -243,13 +246,15 @@ func (db *fakeDB) columnType(table, column string) (typ string, ok bool) {
 }
 
 func (c *fakeConn) isBad() bool {
-	// if not simulating bad conn, do nothing
-	if !c.bad {
+	if c.stickyBad {
+		return true
+	} else if c.bad {
+		// alternate between bad conn and not bad conn
+		c.db.badConn = !c.db.badConn
+		return c.db.badConn
+	} else {
 		return false
 	}
-	// alternate between bad conn and not bad conn
-	c.db.badConn = !c.db.badConn
-	return c.db.badConn
 }
 
 func (c *fakeConn) Begin() (driver.Tx, error) {
@@ -466,7 +471,7 @@ func (c *fakeConn) Prepare(query string) (driver.Stmt, error) {
 		panic("nil c.db; conn = " + fmt.Sprintf("%#v", c))
 	}
 
-	if hookPrepareBadConn != nil && hookPrepareBadConn() {
+	if c.stickyBad || (hookPrepareBadConn != nil && hookPrepareBadConn()) {
 		return nil, driver.ErrBadConn
 	}
 
@@ -529,7 +534,7 @@ func (s *fakeStmt) Exec(args []driver.Value) (driver.Result, error) {
 		return nil, errClosed
 	}
 
-	if hookExecBadConn != nil && hookExecBadConn() {
+	if s.c.stickyBad || (hookExecBadConn != nil && hookExecBadConn()) {
 		return nil, driver.ErrBadConn
 	}
 
@@ -613,7 +618,7 @@ func (s *fakeStmt) Query(args []driver.Value) (driver.Rows, error) {
 		return nil, errClosed
 	}
 
-	if hookQueryBadConn != nil && hookQueryBadConn() {
+	if s.c.stickyBad || (hookQueryBadConn != nil && hookQueryBadConn()) {
 		return nil, driver.ErrBadConn
 	}