Revert "Postgres: Switch the datasource plugin from lib/pq to pgx" (#83760)

Revert "Postgres: Switch the datasource plugin from lib/pq to pgx (#81353)"

This reverts commit 8c18d06386c87f2786119ea9a6334e35e4181cbe.

pkg/tsdb/grafana-postgresql-datasource/locker_test.go

@@ -0,0 +1,63 @@
+package postgres
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIntegrationLocker(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Tests with Sleep")
+	}
+	const notUpdated = "not_updated"
+	const atThread1 = "at_thread_1"
+	const atThread2 = "at_thread_2"
+	t.Run("Should lock for same keys", func(t *testing.T) {
+		updated := notUpdated
+		locker := newLocker()
+		locker.Lock(1)
+		var wg sync.WaitGroup
+		wg.Add(1)
+		defer func() {
+			locker.Unlock(1)
+			wg.Wait()
+		}()
+
+		go func() {
+			locker.RLock(1)
+			defer func() {
+				locker.RUnlock(1)
+				wg.Done()
+			}()
+			require.Equal(t, atThread1, updated, "Value should be updated in different thread")
+			updated = atThread2
+		}()
+		time.Sleep(time.Millisecond * 10)
+		require.Equal(t, notUpdated, updated, "Value should not be updated in different thread")
+		updated = atThread1
+	})
+
+	t.Run("Should not lock for different keys", func(t *testing.T) {
+		updated := notUpdated
+		locker := newLocker()
+		locker.Lock(1)
+		defer locker.Unlock(1)
+		var wg sync.WaitGroup
+		wg.Add(1)
+		go func() {
+			locker.RLock(2)
+			defer func() {
+				locker.RUnlock(2)
+				wg.Done()
+			}()
+			require.Equal(t, notUpdated, updated, "Value should not be updated in different thread")
+			updated = atThread2
+		}()
+		wg.Wait()
+		require.Equal(t, atThread2, updated, "Value should be updated in different thread")
+		updated = atThread1
+	})
+}