Plproxy
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PL/proxy is a PostgreSQL extension that allows writing functions to query other PostgreSQL databases, enabling cross-database queries. It can be used to implement horizontal partitioning by running functions on any, all, or an exact node. However, PL/proxy should still be considered alpha software with limited documentation and stability for some use cases.
![Pl/proxy The PostgreSQL Company Command Prompt, Inc. Joshua D. Drake [email_address]](https://image.slidesharecdn.com/plproxy-1228173200523027-9/85/Plproxy-1-320.jpg)
Plproxy
- 1. Pl/proxy The PostgreSQL Company Command Prompt, Inc. Joshua D. Drake [email_address]
- 2. Purpose Cross database queries Horizontal Partitioning Sort of... Federated databases Gotchas
- 3. Requirements PostgreSQL 8.2.5 Yes it can run on 8.2.0 but nobody runs less than stable release right? PostgreSQL 8.3 But it doesn't exist yet. pgxs apt-get install postgresql-server-dev-8.2 Pgfoundry http://pgfoundry.org/projects/plproxy
- 4. Cross Database Queries Sometimes you just have to: SELECT * FROM dblink('dbname=users_2005 host=192.168.3.254', 'SELECT userid FROM ... But wouldn't it be great if you could: SELECT userid_return('linuxpoet'); You always use functions to control your data flow right?
- 5. So what do we do? (install PL/proxy then...) Create a function on server 192.168.3.5 CREATE OR REPLACE FUNCTION userid_return(text) RETURNS integer AS $$ SELECT CASE WHEN id IS NULL THEN 0 ELSE id END FROM users WHERE username = $1; $$ LANGUAGE 'SQL'; Create a function on localhost CREATE OR REPLACE userid_return(text) RETURNS integer AS $$ CONNECT 'dbname=users_2005 host=192.168.3.254 port=6000'; $$ LANGUAGE 'plproxy';
- 6. Which does what exactly? The function userid_return(text) on the localhost is a thin wrapper to allow execution of a remote function. The two functions must be named identically. The CONNECT argument is used to determine which remote server to connect to.
- 7. If I was a Dolphin mysql> CREATE DATABASE menagerie; mysql> USE menagerie; Database changed Sorry Wrong Database
- 8. Consider remote validity CREATE TABLE sessions (id bigserial PRIMARY KEY, userid integer CHECK(is_valid_user(userid) IS TRUE), sdate timestamp DEFAULT current_timestamp); Function is_valid_user(integer): CREATE OR REPLACE FUNCTION is_valid_user(integer) RETURNS boolean AS $$ CONNECT 'dbname=users_2005 host=192.168.3.254 port=6000'; $$ LANGUAGE 'plproxy';
- 9. Wait, what just happen? Created function on 192.168.3.254 CREATE OR REPLACE FUNCTION is_valid_user(integer) RETURNS boolean AS $$ SELECT CASE WHEN id = $1 THEN TRUE ELSE FALSE END FROM users WHERE id = $1; $$ LANGUAGE 'SQL';
- 10. Then.. on the localhost CREATE OR REPLACE FUNCTION is_valid_user(integer) RETURNS boolean AS $$ CONNECT 'dbname=users_2005 host=192.168.3.254 port=6000'; $$ LANGUAGE 'plproxy'; CREATE TABLE sessions (id bigserial PRIMARY KEY, userid integer CHECK(is_valid_user(userid) IS TRUE), sdate timestamp DEFAULT current_timestamp);
- 11. Lastly to prove the perversion 192.168.3.254> select * from users; id | username | created ----+-----------+---------------------------- 1 | linuxpoet | 2005-10-19 17:44:28.819438 locahost> INSERT INTO sessions (userid,sdate) VALUES (2,current_timestamp); ERROR: new row for relation "sessions" violates check constraint "sessions_userid_check" locahost> INSERT INTO sessions (userid,sdate) VALUES (1,current_timestamp); INSERT 0 1
- 12. Wait, that means... Exactly, you can have a check constraint that checks the validity of data on a local relation against the validity of data on a remote relation.
- 13. Horizontal Partitioning PL/proxy has the ability to not only perform basic data checks on remote partitions but can also use multiple partitions in various ways to achieve greater scalability. ANY – Using the RUN ON 'ANY' method within a PL/proxy function will cause PL/proxy to choose an arbitrary partition to perform the function execution on. (Consider usernames may be on every node).
- 14. ALL or nothing ALL – Using the RUN ON 'ALL” method will cause PL/proxy, to execute the desired function on ”ALL” nodes simultaenously (in parrellel). The key is that it executes simultaneously. You are not waiting for a single partition to return data before the function can be executed on the next partition. Once all results have been returned via the nodes, PL/proxy will then perform a UNION ALL on the data and return it to the client.
- 15. EXACT The RUN ON 'EXACT' mode causes PL/proxy to run on exactly ”1” node. The node is specified within the function body.
- 16. Gotchas PL/proxy should be considered Alpha software. Although it is being used in production by some companies, it is fragile and documentation is non-existant. When used for specific purposes it is very stable. No software should be able to crash the backend.
- 17. Thanks I think the title says it all.