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>Appendix F. Additional Supplied Modules</TD
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><H1
CLASS="SECT1"
><A
NAME="FILE-FDW"
>F.14. file_fdw</A
></H1
><P
>  The <TT
CLASS="FILENAME"
>file_fdw</TT
> module provides the foreign-data wrapper
  <CODE
CLASS="FUNCTION"
>file_fdw</CODE
>, which can be used to access data
  files in the server's file system.  Data files must be in a format
  that can be read by <TT
CLASS="COMMAND"
>COPY FROM</TT
>;
  see <A
HREF="sql-copy.html"
>COPY</A
> for details.
 </P
><P
>  A foreign table created using this wrapper can have the following options:
 </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>filename</TT
></DT
><DD
><P
>     Specifies the file to be read.  Required.  Must be an absolute path name.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>format</TT
></DT
><DD
><P
>     Specifies the file's format,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>FORMAT</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>header</TT
></DT
><DD
><P
>     Specifies whether the file has a header line,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>HEADER</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>delimiter</TT
></DT
><DD
><P
>     Specifies the file's delimiter character,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>DELIMITER</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>quote</TT
></DT
><DD
><P
>     Specifies the file's quote character,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>QUOTE</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>escape</TT
></DT
><DD
><P
>     Specifies the file's escape character,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>ESCAPE</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>null</TT
></DT
><DD
><P
>     Specifies the file's null string,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>NULL</TT
> option.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
>encoding</TT
></DT
><DD
><P
>     Specifies the file's encoding,
     the same as <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>ENCODING</TT
> option.
    </P
></DD
></DL
></DIV
><P
>  A column of a foreign table created using this wrapper can have the
  following options:
 </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>force_not_null</TT
></DT
><DD
><P
>     This is a Boolean option.  If true, it specifies that values of the
     column should not be matched against the null string (that is, the
     file-level <TT
CLASS="LITERAL"
>null</TT
> option).  This has the same effect
     as listing the column in <TT
CLASS="COMMAND"
>COPY</TT
>'s
     <TT
CLASS="LITERAL"
>FORCE_NOT_NULL</TT
> option.
    </P
></DD
></DL
></DIV
><P
>  <TT
CLASS="COMMAND"
>COPY</TT
>'s <TT
CLASS="LITERAL"
>OIDS</TT
> and
  <TT
CLASS="LITERAL"
>FORCE_QUOTE</TT
> options are currently not supported by
  <TT
CLASS="LITERAL"
>file_fdw</TT
>.
 </P
><P
>  These options can only be specified for a foreign table or its columns, not
  in the options of the <TT
CLASS="LITERAL"
>file_fdw</TT
> foreign-data wrapper, nor in the
  options of a server or user mapping using the wrapper.
 </P
><P
>  Changing table-level options requires superuser privileges, for security
  reasons: only a superuser should be able to determine which file is read.
  In principle non-superusers could be allowed to change the other options,
  but that's not supported at present.
 </P
><P
>  For a foreign table using <TT
CLASS="LITERAL"
>file_fdw</TT
>, <TT
CLASS="COMMAND"
>EXPLAIN</TT
> shows
  the name of the file to be read.  Unless <TT
CLASS="LITERAL"
>COSTS OFF</TT
> is
  specified, the file size (in bytes) is shown as well.
 </P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN148264"
></A
><P
><B
>Example F-1. Create a Foreign Table for PostgreSQL CSV Logs</B
></P
><P
>   One of the obvious uses for the <TT
CLASS="LITERAL"
>file_fdw</TT
> is to make
   the PostgreSQL activity log available as a table for querying.  To
   do this, first you must be logging to a CSV file, which here we
   will call <TT
CLASS="LITERAL"
>pglog.csv</TT
>.  First, install <TT
CLASS="LITERAL"
>file_fdw</TT
>
   as an extension:
  </P
><PRE
CLASS="PROGRAMLISTING"
>CREATE EXTENSION file_fdw;</PRE
><P
>   Then create a foreign server:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE SERVER pglog FOREIGN DATA WRAPPER file_fdw;</PRE
><P>
  </P
><P
>   Now you are ready to create the foreign data table.  Using the
   <TT
CLASS="COMMAND"
>CREATE FOREIGN TABLE</TT
> command, you will need to define
   the columns for the table, the CSV file name, and its format:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN TABLE pglog (
  log_time timestamp(3) with time zone,
  user_name text,
  database_name text,
  process_id integer,
  connection_from text,
  session_id text,
  session_line_num bigint,
  command_tag text,
  session_start_time timestamp with time zone,
  virtual_transaction_id text,
  transaction_id bigint,
  error_severity text,
  sql_state_code text,
  message text,
  detail text,
  hint text,
  internal_query text,
  internal_query_pos integer,
  context text,
  query text,
  query_pos integer,
  location text,
  application_name text
) SERVER pglog
OPTIONS ( filename '/home/josh/9.1/data/pg_log/pglog.csv', format 'csv' );</PRE
><P>
  </P
><P
>   That's it &mdash; now you can query your log directly. In production, of course,
   you would need to define some way to adjust to log rotation.
  </P
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