config: add validation for capacity of prepare plan cache (pingcap#14232)

Author: eurekaka

config/config.go

@@ -751,6 +751,9 @@ func (c *Config) Valid() error {
 	if c.AlterPrimaryKey && c.Experimental.AllowAutoRandom {
 		return fmt.Errorf("allow-auto-random is unavailable when alter-primary-key is enabled")
 	}
+	if c.PreparedPlanCache.Capacity < 1 {
+		return fmt.Errorf("capacity in [prepared-plan-cache] should be at least 1")
+	}
 	return nil
 }
 

util/kvcache/simple_lru.go

@@ -48,8 +48,8 @@ type SimpleLRUCache struct {
 // NewSimpleLRUCache creates a SimpleLRUCache object, whose capacity is "capacity".
 // NOTE: "capacity" should be a positive value.
 func NewSimpleLRUCache(capacity uint, guard float64, quota uint64) *SimpleLRUCache {
-	if capacity == 0 {
-		panic("capacity of LRU Cache should be positive.")
+	if capacity < 1 {
+		panic("capacity of LRU Cache should be at least 1.")
 	}
 	return &SimpleLRUCache{
 		capacity: capacity,