Universal File Access Functions

Universal file access functions provide local access interfaces for files on a database server. Only files in the MogDB directory and the log_directory directory can be accessed. Use a relative path for files in the MogDB directory, and a path matching the log_directory configuration setting for log files. Only database initialization users can use these functions.

• pg_ls_dir(dirname text)

  Description: Lists files in a directory.

  Return type: setof text

  Note:pg_ls_dir returns all the names in the specified directory, except the special entries "." and "..".

  For example:

  mogdb=# SELECT pg_ls_dir('./');
        pg_ls_dir
  ----------------------
   .postgresql.conf.swp
   postgresql.conf
   pg_tblspc
   PG_VERSION
   pg_ident.conf
   core
   server.crt
   pg_serial
   pg_twophase
   postgresql.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
   pg_hba.conf
   pg_replslot
   .pg_hba.conf.swp
   cacert.pem
   pg_hba.conf.lock
   global
   mogdb.state
  (32 rows)

• pg_read_file(filename text, offset bigint, length bigint)

  Description: Returns the content of a text file.

  Return type: text

  Note:pg_read_file returns part of a text file. It can return a maximum of length bytes from offset. The actual size of fetched data is less than length if the end of the file is reached first. If offset is negative, it is the length rolled back from the file end. If offset and length are omitted, the entire file is returned.

  For example:

  mogdb=# SELECT pg_read_file('postmaster.pid',0,100);
               pg_read_file
  ---------------------------------------
   53078                                +
   /srv/BigData/hadoop/data1/dbnode+
   1500022474                           +
   8000                                +
   /var/run/FusionInsight               +
   localhost                            +
    2
  (1 row)

• pg_read_binary_file(filename text [, offset bigint, length bigint,missing_ok boolean])

  Description: Returns the content of a binary file.

  Return type: bytea

  Note:pg_read_binary_file is similar to pg_read_file, except that the result is a bytea value; accordingly, no encoding checks are performed. In combination with the convert_from function, this function can be used to read a file in a specified encoding:

  mogdb=# SELECT convert_from(pg_read_binary_file('filename'), 'UTF8');

• pg_stat_file(filename text)

  Description: Returns status information about a file.

  Return type: record

  Note:pg_stat_file returns a record containing the file size, last access timestamp, last modification timestamp, last file status change timestamp, and a Boolean value indicating if it is a directory. Typical use cases are as follows:

  mogdb=# SELECT * FROM pg_stat_file('filename');

  mogdb=# SELECT (pg_stat_file('filename')).modification;

  For example:

  mogdb=# SELECT convert_from(pg_read_binary_file('postmaster.pid'), 'UTF8');
               convert_from
  --------------------------------------
   4881                                +
   /srv/BigData/mogdb/data1/dbnode+
   1496308688                          +
   25108                               +
   /opt/user/Bigdata/mogdb/mogdb_tmp +
   *                                   +
    25108001  43352069                 +
  
  (1 row)

  mogdb=# 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)

  mogdb=# SELECT (pg_stat_file('postmaster.pid')).modification;
        modification
  ------------------------
   2017-06-01 17:18:08+08
  (1 row)