205 lines
6.7 KiB
Go
205 lines
6.7 KiB
Go
// Copyright 2021 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package domain
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import (
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"context"
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"fmt"
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"strconv"
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"sync"
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"github.com/pingcap/tidb/sessionctx"
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"github.com/pingcap/tidb/sessionctx/variable"
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"github.com/pingcap/tidb/util/logutil"
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"github.com/pingcap/tidb/util/sqlexec"
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"github.com/pingcap/tidb/util/stmtsummary"
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"go.uber.org/zap"
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)
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// The sysvar cache replaces the GlobalVariableCache.
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// It is an improvement because it operates similar to privilege cache,
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// where it caches for 5 minutes instead of 2 seconds, plus it listens on etcd
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// for updates from other servers.
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// SysVarCache represents the cache of system variables broken up into session and global scope.
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type SysVarCache struct {
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sync.RWMutex
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global map[string]string
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session map[string]string
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}
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// GetSysVarCache gets the global variable cache.
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func (do *Domain) GetSysVarCache() *SysVarCache {
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return &do.sysVarCache
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}
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func (svc *SysVarCache) rebuildCacheIfNeeded(ctx sessionctx.Context) (err error) {
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svc.RLock()
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cacheNeedsRebuild := len(svc.session) == 0 || len(svc.global) == 0
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svc.RUnlock()
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if cacheNeedsRebuild {
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logutil.BgLogger().Warn("sysvar cache is empty, triggering rebuild")
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if err = svc.RebuildSysVarCache(ctx); err != nil {
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logutil.BgLogger().Error("rebuilding sysvar cache failed", zap.Error(err))
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}
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}
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return err
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}
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// GetSessionCache gets a copy of the session sysvar cache.
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// The intention is to copy it directly to the systems[] map
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// on creating a new session.
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func (svc *SysVarCache) GetSessionCache(ctx sessionctx.Context) (map[string]string, error) {
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if err := svc.rebuildCacheIfNeeded(ctx); err != nil {
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return nil, err
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}
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svc.RLock()
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defer svc.RUnlock()
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// Perform a deep copy since this will be assigned directly to the session
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newMap := make(map[string]string, len(svc.session))
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for k, v := range svc.session {
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newMap[k] = v
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}
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return newMap, nil
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}
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// GetGlobalVar gets an individual global var from the sysvar cache.
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func (svc *SysVarCache) GetGlobalVar(ctx sessionctx.Context, name string) (string, error) {
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if err := svc.rebuildCacheIfNeeded(ctx); err != nil {
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return "", err
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}
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svc.RLock()
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defer svc.RUnlock()
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if val, ok := svc.global[name]; ok {
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return val, nil
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}
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logutil.BgLogger().Warn("could not find key in global cache", zap.String("name", name))
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return "", variable.ErrUnknownSystemVar.GenWithStackByArgs(name)
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}
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func (svc *SysVarCache) fetchTableValues(ctx sessionctx.Context) (map[string]string, error) {
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tableContents := make(map[string]string)
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// Copy all variables from the table to tableContents
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exec := ctx.(sqlexec.RestrictedSQLExecutor)
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stmt, err := exec.ParseWithParams(context.Background(), `SELECT variable_name, variable_value FROM mysql.global_variables`)
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if err != nil {
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return tableContents, err
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}
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rows, _, err := exec.ExecRestrictedStmt(context.TODO(), stmt)
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if err != nil {
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return nil, err
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}
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for _, row := range rows {
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name := row.GetString(0)
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val := row.GetString(1)
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tableContents[name] = val
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}
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return tableContents, nil
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}
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// RebuildSysVarCache rebuilds the sysvar cache both globally and for session vars.
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// It needs to be called when sysvars are added or removed.
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func (svc *SysVarCache) RebuildSysVarCache(ctx sessionctx.Context) error {
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newSessionCache := make(map[string]string)
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newGlobalCache := make(map[string]string)
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tableContents, err := svc.fetchTableValues(ctx)
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if err != nil {
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return err
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}
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for _, sv := range variable.GetSysVars() {
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sVal := sv.Value
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if _, ok := tableContents[sv.Name]; ok {
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sVal = tableContents[sv.Name]
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}
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// session cache stores non-skippable variables, which essentially means session scope.
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// for historical purposes there are some globals, but these should eventually be removed.
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if !sv.SkipInit() {
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newSessionCache[sv.Name] = sVal
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}
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if sv.HasGlobalScope() {
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newGlobalCache[sv.Name] = sVal
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}
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// Propagate any changes to the server scoped variables
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checkEnableServerGlobalVar(sv.Name, sVal)
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}
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logutil.BgLogger().Debug("rebuilding sysvar cache")
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svc.Lock()
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defer svc.Unlock()
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svc.session = newSessionCache
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svc.global = newGlobalCache
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return nil
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}
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// checkEnableServerGlobalVar processes variables that acts in server and global level.
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// This is required because the SetGlobal function on the sysvar struct only executes on
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// the initiating tidb-server. There is no current method to say "run this function on all
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// tidb servers when the value of this variable changes". If you do not require changes to
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// be applied on all servers, use a getter/setter instead! You don't need to add to this list.
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func checkEnableServerGlobalVar(name, sVal string) {
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var err error
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switch name {
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case variable.TiDBEnableStmtSummary:
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err = stmtsummary.StmtSummaryByDigestMap.SetEnabled(sVal, false)
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case variable.TiDBStmtSummaryInternalQuery:
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err = stmtsummary.StmtSummaryByDigestMap.SetEnabledInternalQuery(sVal, false)
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case variable.TiDBStmtSummaryRefreshInterval:
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err = stmtsummary.StmtSummaryByDigestMap.SetRefreshInterval(sVal, false)
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case variable.TiDBStmtSummaryHistorySize:
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err = stmtsummary.StmtSummaryByDigestMap.SetHistorySize(sVal, false)
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case variable.TiDBStmtSummaryMaxStmtCount:
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err = stmtsummary.StmtSummaryByDigestMap.SetMaxStmtCount(sVal, false)
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case variable.TiDBStmtSummaryMaxSQLLength:
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err = stmtsummary.StmtSummaryByDigestMap.SetMaxSQLLength(sVal, false)
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case variable.TiDBCapturePlanBaseline:
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variable.CapturePlanBaseline.Set(sVal, false)
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case variable.TiDBEnableTopSQL:
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variable.TopSQLVariable.Enable.Store(variable.TiDBOptOn(sVal))
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case variable.TiDBTopSQLPrecisionSeconds:
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var val int64
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val, err = strconv.ParseInt(sVal, 10, 64)
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if err != nil {
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break
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}
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variable.TopSQLVariable.PrecisionSeconds.Store(val)
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case variable.TiDBTopSQLMaxStatementCount:
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var val int64
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val, err = strconv.ParseInt(sVal, 10, 64)
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if err != nil {
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break
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}
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variable.TopSQLVariable.MaxStatementCount.Store(val)
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case variable.TiDBTopSQLMaxCollect:
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var val int64
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val, err = strconv.ParseInt(sVal, 10, 64)
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if err != nil {
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break
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}
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variable.TopSQLVariable.MaxCollect.Store(val)
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case variable.TiDBTopSQLReportIntervalSeconds:
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var val int64
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val, err = strconv.ParseInt(sVal, 10, 64)
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if err != nil {
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break
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}
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variable.TopSQLVariable.ReportIntervalSeconds.Store(val)
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}
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if err != nil {
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logutil.BgLogger().Error(fmt.Sprintf("load global variable %s error", name), zap.Error(err))
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}
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}
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