enhance: support configurable estimation on variable legnth field

Signed-off-by: xiaofanluan <[email protected]>

Author: xiaofan-luan

pkg/util/typeutil/varchar_limit.go

@@ -0,0 +1,46 @@
+// Licensed to the LF AI & Data foundation under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package typeutil
+
+import "sync/atomic"
+
+const defaultVarCharEstimateLengthLimit = 256
+
+var varCharEstimateLengthLimit atomic.Int64
+
+func init() {
+	SetVarCharEstimateLengthLimit(defaultVarCharEstimateLengthLimit)
+}
+
+// SetVarCharEstimateLengthLimit updates the global cap applied when estimating
+// record sizes for VarChar fields.
+func SetVarCharEstimateLengthLimit(limit int) {
+	if limit <= 0 {
+		limit = defaultVarCharEstimateLengthLimit
+	}
+	varCharEstimateLengthLimit.Store(int64(limit))
+}
+
+// GetVarCharEstimateLengthLimit returns the current cap used when estimating
+// VarChar field sizes.
+func GetVarCharEstimateLengthLimit() int {
+	limit := int(varCharEstimateLengthLimit.Load())
+	if limit <= 0 {
+		return defaultVarCharEstimateLengthLimit
+	}
+	return limit
+}