[VTAdmin] Insert into schema cache if exists already and not expired

examples/common/scripts/vtctld-up.sh

@@ -36,6 +36,8 @@ vtctld \
  --pprof-http \
   > $VTDATAROOT/tmp/vtctld.out 2>&1 &
 
+echo "Curling \"http://${hostname}:${vtctld_web_port}/debug/status\" to check if vtctld is up"
+
 for _ in {0..300}; do
  curl -I "http://${hostname}:${vtctld_web_port}/debug/status" &>/dev/null && break
  sleep 0.1

go/vt/vtadmin/cache/cache.go

@@ -23,7 +23,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/patrickmn/go-cache"
+	cache "github.com/patrickmn/go-cache"
 
 	"vitess.io/vitess/go/vt/log"
 )
@@ -161,8 +161,13 @@ func (c *Cache[Key, Value]) add(key string, val Value, d time.Duration) error {
 	c.lastFill[key] = time.Now().UTC()
 	c.m.Unlock()
 
-	// Then cache the actual value.
-	return c.cache.Add(key, val, d)
+	_, expr, exists := c.cache.GetWithExpiration(key)
+	if exists && (expr.IsZero() || expr.After(time.Now())) {
+		return c.cache.Replace(key, val, d)
+	} else {
+		// Then cache the actual value.
+		return c.cache.Add(key, val, d)
+	}
 }
 
 // Get returns the Value stored for the key, if present in the cache. If the key

go/vt/vtadmin/cache/cache_test.go

@@ -226,3 +226,48 @@ func TestEnqueueBackfillTimeout(t *testing.T) {
 		assert.Equal(t, q.shouldFail, !ok, "enqueue should %s wait timeout", q.msg)
 	}
 }
+
+func TestUpsertCacheKey(t *testing.T) {
+	var callcount int
+	c := cache.New(func(ctx context.Context, req intkey) (any, error) {
+		time.Sleep(time.Millisecond * 50) // make fills take time so that the second enqueue exceeds WaitTimeout
+		callcount++
+		return nil, nil
+	}, cache.Config{
+		BackfillEnqueueWaitTime: time.Millisecond * 10,
+	})
+
+	var inserts = []struct {
+		shouldFail  bool
+		msg         string
+		key         intkey
+		val         any
+		expectedVal any
+		duration    time.Duration
+	}{
+		{
+			shouldFail:  false,
+			key:         intkey(1),
+			val:         "Old Value",
+			msg:         "first add should succeed",
+			expectedVal: "Old Value",
+		},
+		{
+			shouldFail:  false,
+			key:         intkey(1),
+			val:         "New Value",
+			msg:         "second update should succeed",
+			expectedVal: "New Value",
+		},
+	}
+	for _, tt := range inserts {
+		err := c.Add(tt.key, tt.val, tt.duration)
+		if !tt.shouldFail {
+			assert.Nil(t, err)
+		}
+
+		val, exists := c.Get(tt.key)
+		assert.True(t, exists)
+		assert.Equal(t, val, tt.expectedVal)
+	}
+}