PLPython Fenced Mode

PL/Python is added to the fenced mode, which is insecure. During database compilation, to integrate Python into the database, you can add the –with-python option to configure, or specify the Python path for installing PL/Python and add the –with-includes='/python-dir=path' option.

Before starting the database, set the GUC parameter unix_socket_directory to specify the file address for communication between unix_socket processes. You need to create a folder in user-set-dir-path in advance and grant read, write, and execute permissions on the folder.

unix_socket_directory = '/user-set-dir-path'

After the configuration is complete, start the database.

After PL/Python is added to the database compilation and the GUC parameter unix_socket_directory is set, the fenced-Master process is automatically created during database startup. If Python compilation is not performed for the database, you need to manually start the master process in fenced mode. After the GUC parameter is set, run the command to create the master process.

Run the following command to start the fenced-Master process:

mogdb --fenced -k /user-set-dir-path -D /user-set-dir-path &

After the fenced mode is configured, the UDF calculation is performed in the fenced-worker process for the PL/Python-fenced UDF database.

Usage Guide

Create an extension.
- When the compiled PL/Python is Python 2:
```
MogDB=# create extension plpythonu;
CREATE EXTENSION
```
- When the compiled PL/Python is Python 3:
```
MogDB=# create extension plpython3u;
CREATE EXTENSION
```
The following uses Python 2 as an example.

Create a PL/Python-fenced UDF database.

MogDB=# create or replace function pymax(a int, b int)
MogDB-# returns INT
MogDB-# language plpythonu fenced
MogDB-# as $$
MogDB$# import numpy
MogDB$# if a > b:
MogDB$#     return a;
MogDB$# else:
MogDB$#     return b;
MogDB$# $$;
CREATE FUNCTION

View UDF information.

MogDB=# select * from pg_proc where proname='pymax';
-[ RECORD 1 ]----+--------------
proname          | pymax
pronamespace     | 2200
proowner         | 10
prolang          | 16388
procost          | 100
prorows          | 0
provariadic      | 0
protransform     | -
proisagg         | f
proiswindow      | f
prosecdef        | f
proleakproof     | f
proisstrict      | f
proretset        | f
provolatile      | v
pronargs         | 2
pronargdefaults  | 0
prorettype       | 23
proargtypes      | 23 23
proallargtypes   |
proargmodes      |
proargnames      | {a,b}
proargdefaults   |
prosrc           |
                 | import numpy
                 | if a > b:
                 |     return a;
                 | else:
                 |     return b;
                 |
probin           |
proconfig        |
proacl           |
prodefaultargpos |
fencedmode       | t
proshippable     | f
propackage       | f
prokind          | f
proargsrc        |

Run the UDF.

Create a data table.

MogDB=# create table temp (a int ,b int) ;
CREATE TABLE
MogDB=# insert into temp values (1,2),(2,3),(3,4),(4,5),(5,6);
INSERT 0 5

Run the UDF.

MogDB=# select pymax(a,b) from temp;
 pymax
-------
     2
     3
     4
     5
     6
(5 rows)

Issue