v3.6

SequoiaDB 简介
快速入门
- 快速部署
- 容器模式部署
安装部署
数据库实例
分布式引擎
SAC 管控中心
SequoiaPerf 性能分析工具
参考手册
- SequoiaDB Shell方法
  - Global
    - help()
    - print()
    - sleep()
    - forceGC()
    - showClass()
    - getErr()
    - getLastErrMsg()
    - getLastErrObj()
    - getLastError()
    - setLastErrMsg()
    - setLastErrObj()
    - setLastError()
    - getExePath()
    - getRootPath()
    - getSelfPath()
    - import()
    - importOnce()
    - jsonFormat()
    - traceFmt()
  - Sdb
    - Sdb()
    - analyze()
    - backup()
    - cancelTask()
    - close()
    - createCataRG()
    - createCoordRG()
    - createCS()
    - createDataSource()
    - createDomain()
    - createProcedure()
    - createRG()
    - createSequence()
    - createSpareRG()
    - createUsr()
    - dropCS()
    - dropDataSource()
    - dropDomain()
    - dropSequence()
    - dropUsr()
    - eval()
    - exec()
    - execUpdate()
    - flushConfigure()
    - forceSession()
    - forceStepUp()
    - getCataRG()
    - getCoordRG()
    - getCS()
    - getDataSource()
    - getDomain()
    - getRecycleBin()
    - getRG()
    - getSequence()
    - getSessionAttr()
    - getSpareRG()
    - getTask()
    - invalidateCache()
    - list()
    - listBackup()
    - listCollections()
    - listCollectionSpaces()
    - listDataSources()
    - listDomains()
    - listProcedures()
    - listReplicaGroups()
    - listSequences()
    - listTasks()
    - removeBackup()
    - removeCataRG()
    - removeCoordRG()
    - removeSpareRG()
    - removeProcedure()
    - removeRG()
    - renameCS()
    - renameSequence()
    - resetSnapshot()
    - reloadConf()
    - deleteConf()
    - setSessionAttr()
    - snapshot()
    - startRG()
    - stopRG()
    - sync()
    - setPDLevel()
    - traceOff()
    - traceOn()
    - traceResume()
    - traceStatus()
    - transBegin()
    - transCommit()
    - transRollback()
    - updateConf()
    - waitTasks()
  - SecureSdb
  - SdbCS
    - alter()
    - createCL()
    - dropCL()
    - getCL()
    - getDomainName()
    - listCollections()
    - removeDomain()
    - renameCL()
    - setAttributes()
    - setDomain()
  - SdbCollection
    - aggregate()
    - alter()
    - attachCL()
    - copyIndex()
    - copyIndexAsync()
    - count()
    - createAutoIncrement()
    - createIdIndex()
    - createIndex()
    - createIndexAsync()
    - createLobID()
    - deleteLob()
    - detachCL()
    - disableCompression()
    - disableSharding()
    - dropAutoIncrement()
    - dropIdIndex()
    - dropIndex()
    - dropIndexAsync()
    - enableCompression()
    - enableSharding()
    - find()
    - findOne()
    - getDetail()
    - getIndex()
    - getIndexStat()
    - getLob()
    - getLobDetail()
    - insert()
    - listIndexes()
    - listLobs()
    - putLob()
    - remove()
    - setAttributes()
    - snapshotIndexes()
    - split()
    - splitAsync()
    - truncate()
    - truncateLob()
    - update()
    - upsert()
  - SdbCursor
    - close()
    - current()
    - next()
    - arrayAccess()
  - SdbQuery
    - arrayAccess()
    - close()
    - count()
    - current()
    - explain()
    - flags()
    - getQueryMeta()
    - hint()
    - limit()
    - next()
    - query()
    - remove()
    - size()
    - skip()
    - sort()
    - toArray()
    - update()
  - SdbReplicaGroup
    - attachNode()
    - createNode()
    - detachNode()
    - getDetailObj()
    - getMaster()
    - getNode()
    - getSlave()
    - reelect()
    - removeNode()
    - start()
    - stop()
  - SdbNode
    - connect()
    - getHostName()
    - getDetailObj()
    - getServiceName()
    - start()
    - stop()
  - SdbDomain
    - addGroups()
    - alter()
    - listCollections()
    - listCollectionSpaces()
    - removeGroups()
    - setAttributes()
    - setGroups()
    - listGroups()
  - SdbDataSource
    - alter()
  - SdbRecycleBin
    - alter()
    - count()
    - disable()
    - dropAll()
    - dropItem()
    - enable()
    - getDetail()
    - list()
    - returnItem()
    - returnItemToName()
    - setAttributes()
    - snapshot()
  - SdbSequence
    - fetch()
    - getCurrentValue()
    - getNextValue()
    - restart()
    - setAttributes()
    - setCurrentValue()
  - Oma
    - Oma()
    - addAOmaSvcName()
    - delAOmaSvcName()
    - close()
    - createCoord()
    - createData()
    - createOM()
    - getAOmaSvcName()
    - getIniConfigs()
    - getNodeConfigs()
    - getOmaConfigFile()
    - getOmaConfigs()
    - getOmaInstallFile()
    - getOmaInstallInfo()
    - listNodes()
    - reloadConfigs()
    - removeCoord()
    - removeData()
    - removeOM()
    - setIniConfigs()
    - setNodeConfigs()
    - setOmaConfigs()
    - start()
    - startAllNodes()
    - stopAllNodes()
    - startNode()
    - stopNode()
    - startNodes()
    - stopNodes()
    - updateNodeConfigs()
  - File
    - File()
    - chgrp()
    - chmod()
    - chown()
    - close()
    - copy()
    - exist()
    - find()
    - getSize()
    - getUmask()
    - isDir()
    - isEmptyDir()
    - isFile()
    - list()
    - md5()
    - mkdir()
    - move()
    - read()
    - readContent()
    - readLine()
    - remove()
    - scp()
    - seek()
    - setUmask()
    - stat()
    - write()
    - writeContent()
    - truncate()
  - FileContent
    - clear()
    - getLength()
    - toBase64Code()
  - Cmd
    - Cmd()
    - getCommand()
    - getInfo()
    - getLastOut()
    - getLastRet()
    - run()
    - runJS()
    - start()
  - Remote
    - close()
    - getCmd()
    - getFile()
    - getIniFile()
    - getInfo()
    - getSystem()
    - Remote()
  - Hash
    - fileMD5()
    - md5()
  - IniFile
    - IniFile()
    - addComment()
    - addSectionComment()
    - addLastComment()
    - setComment()
    - setSectionComment()
    - setLastComment()
    - delComment()
    - delSectionComment()
    - delLastComment()
    - enableItem()
    - disableItem()
    - disableAllItem()
    - getComment()
    - getSectionComment()
    - getLastComment()
    - getValue()
    - setValue()
    - toObj()
    - toString()
    - save()
  - Sdbtool
    - listNodes()
  - Ssh
    - Ssh()
    - close()
    - exec()
    - getLastOut()
    - getLastRet()
    - getLocalIP()
    - getPeerIP()
    - pull()
    - push()
  - System
    - addAHostMap
    - addGroup
    - addUser
    - delAHostMap
    - delGroup
    - delUser
    - getAHostMap
    - getCpuInfo
    - getCurrentUser
    - getDiskInfo
    - getEWD
    - getHostName
    - getHostsMap
    - getIpTablesInfo
    - getMemInfo
    - getNetcardInfo
    - getPID
    - getProcUlimitConfigs
    - getReleaseInfo
    - getSystemConfigs
    - getTID
    - getUserEnv
    - isGroupExist
    - isProcExist
    - isUserExist
    - killProcess
    - listAllUsers
    - listGroups
    - listLoginUsers
    - listProcess
    - ping
    - runService
    - setProcUlimitConfigs
    - setUserConfigs
    - snapshotCpuInfo
    - snapshotDiskInfo
    - snapshotMemInfo
    - snapshotNetcardInfo
    - sniffPort
    - type
  - 辅助类型对象
    - SdbSnapshotOption
    - SdbQueryOption
    - SdbTraceOption
    - CLCount
    - User
    - CipherUser
  - 特殊类型对象
    - BinData
    - BSONArray
    - BSONObj
    - MaxKey
    - MinKey
    - NumberDecimal
    - NumberLong
    - OID
    - Regex
    - SdbDate
    - Timestamp
  - 命令位置参数
- 错误码
- 连接器
  - Hadoop
    - 部署
    - 集成
  - Hive
- 操作符
  - 匹配符
    - $gt
    - $gte
    - $lt
    - $lte
    - $ne
    - $et
    - $mod
    - $in
    - $isnull
    - $nin
    - $all
    - $and
    - $not
    - $or
    - $exists
    - $elemMatch
    - $+标识符
    - $regex
    - $expand
    - $returnMatch
  - 选择符
  - 函数操作
    - $abs
    - $ceiling
    - $floor
    - $mod
    - $add
    - $subtract
    - $multiply
    - $divide
    - $substr
    - $strlen
    - $strlenBytes
    - $strlenCP
    - $lower
    - $upper
    - $ltrim
    - $rtrim
    - $trim
    - $cast
    - $size
    - $type
    - $slice
  - 更新符
    - $inc
    - $set
    - $unset
    - $bit
    - $rename
    - $addtoset
    - $pop
    - $pull
    - $pull_all
    - $pull_by
    - $pull_all_by
    - $push
    - $push_all
    - $replace
  - 聚集符
    - $project
    - $match
    - $limit
    - $sort
    - $skip
    - $group
    - SQL to Aggregate 映射表
  - 字段操作符
    - $field
- SQL to SequoiaDB 映射表
- SQL语法
- 编目表
- 数据库快照
- 数据库列表
- 访问计划的评估过程
- Web服务
  - WebSphere
    - 部署
    - 连接
    - web应用
  - Tomcat
    - 部署
    - 连接
    - web应用
  - JBoss
    - 部署
    - 连接
    - web应用
- 限制
常见问题及解答（FAQ）
- SequoiaDB FAQ
- SQL FAQ
版本信息

clear()

名称

clear - 清除缓冲区内容

语法

content.clear()

类别

FileContent

描述

清除缓冲区内容

参数

无

返回值

无

错误

如果出错则抛异常，并输出错误信息，可以通过getLastErrMsg()获取错误信息或通过getLastError()获取错误码。关于错误处理可以参考常见错误处理指南。

常见错误可参考错误码。

版本

v3.2 及以上版本

示例

打开一个二进制文件，获取文件描述符

> var file = new File( "/opt/sequoiadb/file.dump" )

读取文件内容到 fileContent 对象中（详细可参考命令File::readContent）
```
> var content = file.readContent( 10000 )
```
清除缓冲区内容
```
> content.clear()
```

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