GaussDB-通用文件访问函数
通用文件访问函数提供了对数据库服务器上的文件的本地访问接口。只有数据库集群目录和log_directory目录里面的文件可以访问。使用相对路径访问集群目录里面的文件，以及匹配log_directory配置而设置的路径访问日志文件。只有数据库初始化用户才能使用这些函数。
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pg_ls_dir(dirname text)
返回值类型：setof text
备注：pg_ls_dir返回指定目录里面的除了特殊项“.”和“..”之外所有名称。
示例：
| ``` gaussdb=# SELECT pg_ls_dir('./'); pg_ls_dir ---------------------- .gaussdb.conf.swp gaussdb.conf pg_tblspc PG_VERSION gs_ident.conf core server.crt pg_serial pg_twophase gaussdb.conf.lock pg_stat_tmp pg_notify pg_subtrans pg_ctl.lock pg_xlog pg_clog base pg_snapshots postmaster.opts postmaster.pid server.key.rand server.key.cipher pg_multixact pg_errorinfo server.key gs_hba.conf pg_replslot .gs_hba.conf.swp cacert.pem gs_hba.conf.lock global gaussdb.state (32 rows)
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pg_read_file(filename text, offset bigint, length bigint)
返回值类型：text
备注：pg_read_file返回一个文本文件的一部分，从offset开始，最多返回length字节（如果先达到文件结尾，则小于这个数值）。如果offset是负数，则它是相对于文件结尾回退的长度。如果省略了offset和length，则返回整个文件。
示例：
| ``` gaussdb=# SELECT pg_read_file('postmaster.pid',0,100); pg_read_file --------------------------------------- 53078 + /srv/BigData/testdir/data1/coordinator+ 1500022474 + 8000 + /var/run/FusionInsight + localhost + 2 (1 row)
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pg_read_binary_file(filename text [, offset bigint, length bigint,missing_ok boolean])
返回值类型：bytea
备注：pg_read_binary_file的功能与pg_read_file类似，除了结果的返回值为bytea类型不一致，相应地不会执行编码检查。与convert_from函数结合，这个函数可以用来读取用指定编码的一个文件。
| ``` gaussdb=# SELECT convert_from(pg_read_binary_file('filename'), 'UTF8');
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pg_stat_file(filename text)
返回值类型：record
备注：pg_stat_file返回一条记录，其中包含：文件大小、最后访问时间戳、最后更改时间戳、最后文件状态修改时间戳以及标识传入参数是否为目录的Boolean值。典型的用法：
| ``` gaussdb=# SELECT * FROM pg_stat_file('filename');
| ---------------------------------------------------------- | | ``` gaussdb=# SELECT (pg_stat_file('filename')).modification; ``` | | ------------------------------------------------------------------ | 示例： | ``` gaussdb=# SELECT convert_from(pg_read_binary_file('postmaster.pid'), 'UTF8'); convert_from -------------------------------------- 4881 + /srv/BigData/gaussdb/data1/coordinator+ 1496308688 + 25108 + /opt/huawei/Bigdata/gaussdb/gaussdb_tmp + * + 25108001 43352069 + (1 row) ``` | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ``` gaussdb=# SELECT * FROM pg_stat_file('postmaster.pid'); size | access | modification | change | creation | isdir ------+------------------------+------------------------+------------------------ +----------+------- 117 | 2017-06-05 11:06:34+08 | 2017-06-01 17:18:08+08 | 2017-06-01 17:18:08+08 | | f (1 row) ``` | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ``` gaussdb=# SELECT (pg_stat_file('postmaster.pid')).modification; modification ------------------------ 2017-06-01 17:18:08+08 (1 row) ``` | | ---------------------------------------------------------------------------------------------------------------------------------------------------------- |
更多详情请参考GaussDB 文档中心：doc.hcs.huawei.com/db/zh-cn/ga…
