Universal File Access Functions¶
Universal file access functions provide local access interfaces for files on a database server. Only files in the database cluster directory and the log_directory directory can be accessed. Use a relative path for files in the cluster directory, and a path matching the log_directory configuration setting for log files. Only database system administrators 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 "..".
Examples:
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
gaussdb.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.
Examples:
SELECT pg_read_file('postmaster.pid',0,100);
pg_read_file
---------------------------------------
53078 +
/srv/BigData/hadoop/data1/coordinator+
1500022474 +
8000 +
/var/run/dws +
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:
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:
SELECT * FROM pg_stat_file('filename');
SELECT (pg_stat_file('filename')).modification;
Examples:
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)
SELECT (pg_stat_file('postmaster.pid')).modification;
modification
------------------------
2017-06-01 17:18:08+08
(1 row)