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>Appendix F. Additional Supplied Modules</TD
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CLASS="SECT1"
><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.
Access to such data files is currently read-only.
</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
> Note that while <TT
CLASS="COMMAND"
>COPY</TT
> allows options such as OIDS and HEADER
to be specified without a corresponding value, the foreign data wrapper
syntax requires a value to be present in all cases. To activate
<TT
CLASS="COMMAND"
>COPY</TT
> options normally supplied without a value, you can
instead pass the value TRUE.
</P
><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="AEN152053"
></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 — now you can query your log directly. In production, of
course, you would need to define some way to deal with log rotation.
</P
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