tidb utils 源码
tidb utils 代码
文件路径：/executor/utils.go
// Copyright 2021 PingCAP, Inc.
//
// Licensed 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 executor
import (
"strings"
)
// SetFromString constructs a slice of strings from a comma separated string.
// It is assumed that there is no duplicated entry. You could use addToSet to maintain this property.
// It is exported for tests. I HOPE YOU KNOW WHAT YOU ARE DOING.
func SetFromString(value string) []string {
if len(value) == 0 {
return nil
}
return strings.Split(value, ",")
}
func setToString(set []string) string {
return strings.Join(set, ",")
}
// addToSet add a value to the set, e.g:
// addToSet("Select,Insert,Update", "Update") returns "Select,Insert,Update".
func addToSet(set []string, value string) []string {
for _, v := range set {
if v == value {
return set
}
}
return append(set, value)
}
// deleteFromSet delete the value from the set, e.g:
// deleteFromSet("Select,Insert,Update", "Update") returns "Select,Insert".
func deleteFromSet(set []string, value string) []string {
for i, v := range set {
if v == value {
copy(set[i:], set[i+1:])
return set[:len(set)-1]
}
}
return set
}
// batchRetrieverHelper is a helper for batch returning data with known total rows. This helps implementing memtable
// retrievers of some information_schema tables. Initialize `batchSize` and `totalRows` fields to use it.
type batchRetrieverHelper struct {
// When retrieved is true, it means retrieving is finished.
retrieved bool
// The index that the retrieving process has been done up to (exclusive).
retrievedIdx int
batchSize int
totalRows int
}
// nextBatch calculates the index range of the next batch. If there is such a non-empty range, the `retrieveRange` func
// will be invoked and the range [start, end) is passed to it. Returns error if `retrieveRange` returns error.
func (b *batchRetrieverHelper) nextBatch(retrieveRange func(start, end int) error) error {
if b.retrievedIdx >= b.totalRows {
b.retrieved = true
}
if b.retrieved {
return nil
}
start := b.retrievedIdx
end := b.retrievedIdx + b.batchSize
if end > b.totalRows {
end = b.totalRows
}
err := retrieveRange(start, end)
if err != nil {
b.retrieved = true
return err
}
b.retrievedIdx = end
if b.retrievedIdx == b.totalRows {
b.retrieved = true
}
return nil
}
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