database/sql: reduce lock contention in Stmt.connStmt
Previouslly, Stmt.connStmt calls DB.connIfFree on each Stmt.css.
Since Stmt.connStmt locks Stmt.mu, a concurrent use of Stmt causes lock
contention on Stmt.mu.
Additionally, DB.connIfFree locks DB.mu which is shared by DB.addDep and
DB.removeDep.
This change removes DB.connIfFree and makes use of a first unused
connection in idle connection pool to reduce lock contention
without making it complicated.
Fixes #9484
On EC2 c3.8xlarge (E5-2680 v2 @ 2.80GHz * 32 vCPU):
benchmark old ns/op new ns/op delta
BenchmarkManyConcurrentQuery-8 40249 34721 -13.73%
BenchmarkManyConcurrentQuery-16 45610 40176 -11.91%
BenchmarkManyConcurrentQuery-32 109831 43179 -60.69%
benchmark old allocs new allocs delta
BenchmarkManyConcurrentQuery-8 25 25 +0.00%
BenchmarkManyConcurrentQuery-16 25 25 +0.00%
BenchmarkManyConcurrentQuery-32 25 25 +0.00%
benchmark old bytes new bytes delta
BenchmarkManyConcurrentQuery-8 3980 3969 -0.28%
BenchmarkManyConcurrentQuery-16 3980 3982 +0.05%
BenchmarkManyConcurrentQuery-32 3993 3990 -0.08%
Change-Id: Ic96296922c465bac38a260018c58324dae1531d9
Reviewed-on: https://go-review.googlesource.com/2207
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 34efdf2..60bdefa 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -1764,56 +1764,6 @@
wg.Wait()
}
-func manyConcurrentQueries(t testing.TB) {
- maxProcs, numReqs := 16, 500
- if testing.Short() {
- maxProcs, numReqs = 4, 50
- }
- defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(maxProcs))
-
- db := newTestDB(t, "people")
- defer closeDB(t, db)
-
- stmt, err := db.Prepare("SELECT|people|name|")
- if err != nil {
- t.Fatal(err)
- }
- defer stmt.Close()
-
- var wg sync.WaitGroup
- wg.Add(numReqs)
-
- reqs := make(chan bool)
- defer close(reqs)
-
- for i := 0; i < maxProcs*2; i++ {
- go func() {
- for range reqs {
- rows, err := stmt.Query()
- if err != nil {
- t.Errorf("error on query: %v", err)
- wg.Done()
- continue
- }
-
- var name string
- for rows.Next() {
- rows.Scan(&name)
- }
- rows.Close()
-
- wg.Done()
- }
- }()
- }
-
- for i := 0; i < numReqs; i++ {
- reqs <- true
- }
-
- wg.Wait()
-}
-
func TestIssue6081(t *testing.T) {
db := newTestDB(t, "people")
defer closeDB(t, db)
@@ -1985,3 +1935,31 @@
doConcurrentTest(b, ct)
}
}
+
+func BenchmarkManyConcurrentQueries(b *testing.B) {
+ b.ReportAllocs()
+ // To see lock contention in Go 1.4, 16~ cores and 128~ goroutines are required.
+ const parallelism = 16
+
+ db := newTestDB(b, "magicquery")
+ defer closeDB(b, db)
+ db.SetMaxIdleConns(runtime.GOMAXPROCS(0) * parallelism)
+
+ stmt, err := db.Prepare("SELECT|magicquery|op|op=?,millis=?")
+ if err != nil {
+ b.Fatal(err)
+ }
+ defer stmt.Close()
+
+ b.SetParallelism(parallelism)
+ b.RunParallel(func(pb *testing.PB) {
+ for pb.Next() {
+ rows, err := stmt.Query("sleep", 1)
+ if err != nil {
+ b.Error(err)
+ return
+ }
+ rows.Close()
+ }
+ })
+}
