Postgresql Federation

Who Am I?
●

Jim Mlodgenski
–
–

●

jimm@openscg.com
@jim_mlodgenski

Co-organizer of
–
–

●

NYC PUG (www.nycpug.org)
Philly PUG (www.phlpug.org)

CTO, OpenSCG
–

www.openscg.com

http://nyc.pgconf.us

What is a federated database?
“A federated database system is a type of meta-database
management system (DBMS), which transparently maps
multiple autonomous database systems into a single federated
database. The constituent databases are interconnected via a
computer network and may be geographically decentralized. ...
There is no actual data integration in the constituent disparate
databases as a result of data federation.”
-Wikipedia

How does PostgreSQL do it?
●

Uses Foreign Table Wrappers (FDW)

●

Used with SQL/MED
–
–

Management of External Data

–
●

New ANIS SQL 2003 Extension
Standard way of handling remote objects in SQL databases

Wrappers used by SQL/MED to access remotes data
sources

Types of Foreign Data Wrappers
●

SQL

●

NoSQL

●

File

●

Miscellaneous

●

PostgreSQL

SQL Wrappers
●

Oracle

●

SQLite

●

MySQL

●

JDBC

●

Informix

●

ODBC

●

Firebird

SQL Wrappers
CREATE SERVER oracle_server FOREIGN DATA WRAPPER
oracle_fdw OPTIONS (dbserver 'ORACLE_DBNAME');
CREATE USER MAPPING FOR CURRENT_USER
SERVER oracle_server
OPTIONS (user 'scott', password 'tiger');
CREATE FOREIGN TABLE fdw_test (
userid

numeric,

username

text,

email

text

)
SERVER oracle_server
OPTIONS ( schema 'scott', table 'fdw_test');
postgres=# select * from fdw_test;
userid | username |

email

--------+----------+------------------1 | scott
(1 row)

| scott@oracle.com

NoSQL Wrappers
●

MongoDB

●

Redis

●

CouchDB

●

Neo4j

●

MonetDB

●

Tycoon

NoSQL Wrappers
CREATE SERVER mongo_server FOREIGN DATA WRAPPER
mongo_fdw OPTIONS (address '192.168.122.47', port '27017');
CREATE FOREIGN TABLE databases (
_id NAME,
name TEXT
)
SERVER mongo_server
OPTIONS (database 'mydb', collection 'pgData');
test=# select * from databases ;
_id

|

name

--------------------------+-----------52fd49bfba3ae4ea54afc459 | mongo
52fd49bfba3ae4ea54afc45a | postgresql
52fd49bfba3ae4ea54afc45b | oracle
52fd49bfba3ae4ea54afc45c | mysql
52fd49bfba3ae4ea54afc45d | redis
52fd49bfba3ae4ea54afc45e | db2
(6 rows)

File Wrappers
●

Delimited files

●

Fixed length files

●

JSON files

File Wrappers
CREATE SERVER pg_load FOREIGN DATA WRAPPER file_fdw;
CREATE FOREIGN TABLE leads (
first_name text, last_name text,
company_name text, address text,
city text, county text,
state text, zip text,
phone1 text, phone2 text,
email text, web text
) SERVER pg_load
OPTIONS ( filename '/tmp/us-500.csv', format 'csv', header 'TRUE' );
test=# select first_name || ' ' || last_name as full_name, email from leads limit 3;
full_name

|

email

-------------------+------------------------------James Butt

| jbutt@gmail.com

Josephine Darakjy | josephine_darakjy@darakjy.org
Art Venere
(3 rows)

| art@venere.org

Miscellaneous Wrappers
●

Hadoop

●

LDAP

●

S3

●

WWW

●

PG-Strom

Hadoop Wrapper
CREATE SERVER hive_server FOREIGN DATA WRAPPER
hive_fdw OPTIONS (address '127.0.0.1', port '10000');
CREATE USER MAPPING

FOR PUBLIC SERVER hive_server;

CREATE FOREIGN TABLE order_line (
ol_w_id

integer,

ol_d_id

integer,

ol_o_id

integer,

ol_number

integer,

ol_i_id

integer,

ol_delivery_d

timestamp,

ol_amount

decimal(6,2),

ol_supply_w_id

integer,

ol_quantity

decimal(2,0),

ol_dist_info

varchar(24)

) SERVER hive_server OPTIONS (table 'order_line');
INSERT INTO item_sale_month
SELECT ol_i_id as i_id,
EXTRACT(YEAR FROM ol_delivery_d) as year,
EXTRACT(MONTH FROM ol_delivery_d) as month,
sum(ol_amount) as amount
FROM order_line
GROUP BY 1, 2, 3;

Hadoop Wrapper
●

Hadoop foreign tables can also be writable
CREATE FORIEGN TABLE audit (
audit_id

bigint,

event_d

timestamp,

table

varchar,

action

varchar,

user

varchar,

) SERVER hive_server
OPTIONS (table 'audit',
flume_port '44444');
INSERT INTO audit
VALUES (nextval('audit_id_seq'), now(), 'users', 'SELECT', 'scott');

Hadoop Wrapper
●

It also works with HBase tables
CREATE FOREIGN TABLE hive_hbase_table (
key

varchar,

value varchar
) SERVER localhive
OPTIONS (table 'hbase_table', hbase_address 'localhost',
hbase_port '9090', hbase_mapping ':key,cf:val');
INSERT INTO hive_hbase_table VALUES ('key1', 'value1');
INSERT INTO hive_hbase_table VALUES ('key2', 'value2');
UPDATE hive_hbase_table SET value = 'update' WHERE key = 'key2';
DELETE FROM hive_hbase_table WHERE key='key1';
SELECT * from hive_hbase_table;

WWW Wrapper
CREATE SERVER www_fdw_server_google_search FOREIGN DATA WRAPPER www_fdw
OPTIONS (uri 'https://ajax.googleapis.com/ajax/services/search/web?v=1.0');
CREATE USER MAPPING FOR current_user SERVER www_fdw_server_google_search;
CREATE FOREIGN TABLE www_fdw_google_search (
q text, GsearchResultClass text, unescapedUrl text, url text,
visibleUrl text, cacheUrl text, title text, titleNoFormatting text, content text
) SERVER www_fdw_server_google_search;
select url,substring(title,1,25)||'...',substring(content,1,25)||'...'
from www_fdw_google_search where q='postgresql fdw';
url

|

?column?

|

?column?

-------------------------------------------------------------+------------------------------+-----------------------------http://wiki.postgresql.org/wiki/Foreign_data_wrappers

| Foreign data wrappers - <... | Jan 24, 2014 ... 1...

http://www.postgresql.org/docs/9.3/static/postgres-fdw.html | PostgreSQL: Docume... | F.31.1. FDW Option...
http://www.postgresql.org/docs/9.3/static/fdwhandler.html

| PostgreSQL: Docume... | Foreign Data Wrapper Call...

http://www.craigkerstiens.com/2013/08/05/a-look-at-FDWs/

| A look at Foreign Data Wr... | Aug 5, 2013 ... An...

(4 rows)

PostgreSQL Wrapper
●

The most functional FDW by far

●

Replaces much of the functionality of dblink

●

Shipped as a contrib module

PostgreSQL Wrapper
CREATE SERVER postgres_server FOREIGN DATA WRAPPER postgres_fdw
OPTIONS (host 'localhost', port '5432', dbname 'test2');
CREATE USER MAPPING FOR PUBLIC SERVER postgres_server;
CREATE FOREIGN TABLE bird_strikes (
aircraft_type varchar, airport varchar, altitude varchar, aircraft_model varchar,
num_wildlife_struck varchar, impact_to_flight varchar, effect varchar,
location varchar, flight_num varchar, flight_date timestamp,
record_id int, indicated_damage varchar, freeform_en_route varchar, num_engines varchar,
airline varchar, origin_state varchar, phase_of_flight varchar, precipitation varchar,
wildlife_collected boolean, wildlife_sent_to_smithsonian boolean, remarks varchar,
reported_date timestamp, wildlife_size varchar, sky_conditions varchar, wildlife_species varchar,
when_time_hhmm varchar, time_of_day varchar, pilot_warned varchar,
cost_out_of_service varchar, cost_other varchar, cost_repair varchar, cost_total varchar,
miles_from_airport varchar, feet_above_ground varchar, num_human_fatalities integer,
num_injured integer, speed_knots varchar
) SERVER postgres_server OPTIONS (table_name 'bird_strikes');

PostgreSQL Wrapper
●

Only requests columns that are needed
test=# explain verbose select airport, flight_date from bird_strikes;
QUERY PLAN
------------------------------------------------------------------------------Foreign Scan on public.bird_strikes

(cost=100.00..148.40 rows=1280 width=40)

Output: airport, flight_date
Remote SQL: SELECT airport, flight_date FROM public.bird_strikes
(3 rows)

PostgreSQL Wrapper
●

Sends a WHERE clause
test=# explain verbose select airport, flight_date from
bird_strikes where flight_date > '2011-01-01';
QUERY PLAN
-----------------------------------------------------------------Foreign Scan on public.bird_strikes
rows=427 width=40)

(cost=100.00..134.54

Remote SQL: SELECT airport, flight_date FROM
public.bird_strikes WHERE ((flight_date > '2011-01-01
00:00:00'::timestamp without time zone))
(3 rows)

PostgreSQL Wrapper
●

Sends built-in immutable functions
test=# explain verbose select airport, flight_date from bird_strikes where flight_date
> '2011-01-01' and length(airport) < 10;
QUERY PLAN
------------------------------------------------------------------------------Foreign Scan on public.bird_strikes

(cost=100.00..135.24 rows=142 width=40)

Remote SQL: SELECT airport, flight_date FROM public.bird_strikes WHERE ((flight_date
> '2011-01-01 00:00:00'::timestamp without time zone)) AND ((length(airport) < 10))
(3 rows)

PostgreSQL Wrapper
●

Writable (INSERT, UPDATE, DELETE)
test=# explain verbose update bird_strikes set airport = 'Unknown' where record_id = 313339;
QUERY PLAN
------------------------------------------------------------------------------Update on public.bird_strikes

(cost=100.00..111.05 rows=1 width=964)

Remote SQL: UPDATE public.bird_strikes SET airport = $2 WHERE ctid = $1
->

Foreign Scan on public.bird_strikes

(cost=100.00..111.05 rows=1 width=964)

Output: aircraft_type, 'Unknown'::character varying, altitude, aircraft_model, num_wildlife_struck,
impact_to_flight, effect, location, flight_num, flight_date, record_id, indicated_damage, freefo
rm_en_route, num_engines, airline, origin_state, phase_of_flight, precipitation, wildlife_collected,
wildlife_sent_to_smithsonian, remarks, reported_date, wildlife_size, sky_conditions, wildlife_species, w
hen_time_hhmm, time_of_day, pilot_warned, cost_out_of_service, cost_other, cost_repair, cost_total, miles_from_airport,
feet_above_ground, num_human_fatalities, num_injured, speed_knots, ctid
Remote SQL: SELECT aircraft_type, altitude, aircraft_model, num_wildlife_struck, impact_to_flight, effect,
location, flight_num, flight_date, record_id, indicated_damage, freeform_en_route, num_en
gines, airline, origin_state, phase_of_flight, precipitation, wildlife_collected, wildlife_sent_to_smithsonian, remarks,
reported_date, wildlife_size, sky_conditions, wildlife_species, when_time_hhmm, time
_of_day, pilot_warned, cost_out_of_service, cost_other, cost_repair, cost_total, miles_from_airport, feet_above_ground,
num_human_fatalities, num_injured, speed_knots, ctid FROM public.bird_strikes WHERE (
(record_id = 313339)) FOR UPDATE
(5 rows)

PostgreSQL Wrapper
●

Writes are transactional
test=# select airport from bird_strikes where record_id = 313339;
airport
--------Unknown
(1 row)
test=# BEGIN;
BEGIN
test=# update bird_strikes set airport = 'UNKNOWN' where record_id = 313339;
UPDATE 1
test=# ROLLBACK;
ROLLBACK
test=# select airport from bird_strikes where record_id = 313339;
airport
--------Unknown
(1 row)

Limitations
●

Aggregates are not pushed down
test=# explain verbose select count(*) from bird_strikes;
QUERY PLAN
--------------------------------------------------------------------------------------------------------Aggregate

(cost=220.92..220.93 rows=1 width=0)

Output: count(*)
->


(cost=100.00..212.39 rows=3413 width=0)

Output: aircraft_type, airport, altitude, aircraft_model, num_wildlife_struck, impact_to_flight, effect,
location, flight_num, flight_date, record_id, indicated_damage, freeform_en_route, num_engi
nes, airline, origin_state, phase_of_flight, precipitation, wildlife_collected, wildlife_sent_to_smithsonian,
remarks, reported_date, wildlife_size, sky_conditions, wildlife_species, when_time_hhmm, time_o
f_day, pilot_warned, cost_out_of_service, cost_other, cost_repair, cost_total, miles_from_airport,
feet_above_ground, num_human_fatalities, num_injured, speed_knots
Remote SQL: SELECT NULL FROM public.bird_strikes
(5 rows)

Limitations
●

ORDER BY, GROUP BY, LIMIT not pushed down
test=# explain verbose select flight_num from bird_strikes order by flight_date limit 5;
QUERY PLAN
------------------------------------------------------------------------------------------Limit

(cost=169.66..169.67 rows=5 width=40)

Output: flight_num, flight_date
->

Sort

(cost=169.66..172.86 rows=1280 width=40)

Sort Key: bird_strikes.flight_date
->


(cost=100.00..148.40 rows=1280 width=40)

Remote SQL: SELECT flight_num, flight_date FROM public.bird_strikes
(8 rows)

Limitations
●

Joins not pushed down
test=# explain verbose select s.name, b.flight_date
test-# from bird_strikes b, state_code s
test-# where b.location = s.abbreviation and flight_date > '2011-01-01';
QUERY PLAN
------------------------------------------------------------------------------Hash Join

(cost=239.88..349.95 rows=1986 width=40)

Output: s.name, b.flight_date
Hash Cond: ((s.abbreviation)::text = (b.location)::text)
->

Foreign Scan on public.state_code s

(cost=100.00..137.90 rows=930 width=64)

Output: s.id, s.name, s.abbreviation, s.country, s.type, s.sort, s.status, s.occupied, s.notes, s.fips_state, s.assoc_press,
s.standard_federal_region, s.census_region, s.census_region_name, s.cen
sus_division, s.census_devision_name, s.circuit_court
Remote SQL: SELECT name, abbreviation FROM public.state_code
->

Hash

(cost=134.54..134.54 rows=427 width=40)

Output: b.flight_date, b.location
->

Foreign Scan on public.bird_strikes b

(cost=100.00..134.54 rows=427 width=40)

Output: b.flight_date, b.location
Remote SQL: SELECT location, flight_date FROM public.bird_strikes WHERE ((flight_date > '2011-01-01 00:00:00'::timestamp
without time zone))
(11 rows)

Limitations (Gotcha)
●

Sometimes the foreign tables don't act like tables
test=# SELECT l.*, w.lat, w.lng
FROM leads l, www_fdw_geocoder_google w
WHERE w.address = l.address || ',' || l.city || ',' || l.state;
first_name | last_name | company_name | address | city | county |
state | zip | phone1 | phone2 | email | web | lat | lng
------------+-----------+--------------+---------+------+-------+-------+-----+--------+--------+-------+-----+-----+----(0 rows)

QUERY PLAN
------------------------------------------------------------------------------------------Merge Join

(cost=187.47..215.47 rows=1000 width=448)

Output: l.first_name, l.last_name, l.company_name, l.address, l.city, l.county, l.state, l.zip, l.phone1, l.phone2, l.email, l.web, w.lat,
w.lng
Merge Cond: ((((((l.address || ','::text) || l.city) || ','::text) || l.state)) = w.address)
->

Sort

(cost=37.64..38.14 rows=200 width=384)

Output: l.first_name, l.last_name, l.company_name, l.address, l.city, l.county, l.state, l.zip, l.phone1, l.phone2, l.email, l.web,
(((((l.address || ','::text) || l.city) || ','::text) || l.state
))
Sort Key: (((((l.address || ','::text) || l.city) || ','::text) || l.state))
->

Foreign Scan on public.leads l

(cost=0.00..30.00 rows=200 width=384)

Output: l.first_name, l.last_name, l.company_name, l.address, l.city, l.county, l.state, l.zip, l.phone1, l.phone2, l.email,
l.web, ((((l.address || ','::text) || l.city) || ','::text) || l.
state)
Foreign File: /tmp/us-500.csv
Foreign File Size: 81485
->

Sort

(cost=149.83..152.33 rows=1000 width=96)

Output: w.lat, w.lng, w.address
Sort Key: w.address
->

Foreign Scan on public.www_fdw_geocoder_google w
Output: w.lat, w.lng, w.address
WWW API: Request

(16 rows)

(cost=0.00..100.00 rows=1000 width=96)

CREATE OR REPLACE FUNCTION google_geocode(
OUT first_name text, OUT last_name text, OUT company_name text, OUT address text, OUT city text, OUT county text,
OUT state text, OUT zip text, OUT phone1 text, OUT phone2 text, OUT email text, OUT web text, OUT lat text, OUT lng text)
RETURNS SETOF RECORD AS $$
DECLARE
r

record;

f_adr text;
l_lat text;
l_lng text;
BEGIN
FOR r IN SELECT * FROM leads LOOP
f_adr := r.address || ',' || r.city || ',' || r.state;
EXECUTE 'SELECT lat, lng FROM www_fdw_geocoder_google WHERE address = $1'
INTO l_lat, l_lng
USING f_adr;
SELECT

r.first_name, r.last_name, r.company_name, r.address, r.city, r.county, r.state, r.zip,
r.phone1, r.phone2, r.email, r.web, l_lat, l_lng

INTO first_name, last_name, company_name, address, city, county, state, zip,
phone1, phone2, email, web, lat, lng;
RETURN NEXT;
END LOOP;
END $$ LANGUAGE plpgsql;

Writing a new FDW
●

Might not need to write one if there is a http interface

●

Use the Blackhole as a template
–

https://bitbucket.org/adunstan/blackhole_fdw

Writing a new FDW
Datum blackhole_fdw_handler(PG_FUNCTION_ARGS){
...
/* these are required */
fdwroutine->GetForeignRelSize = blackholeGetForeignRelSize;
fdwroutine->GetForeignPaths = blackholeGetForeignPaths;
fdwroutine->GetForeignPlan = blackholeGetForeignPlan;
fdwroutine->BeginForeignScan = blackholeBeginForeignScan;
fdwroutine->IterateForeignScan = blackholeIterateForeignScan;
fdwroutine->ReScanForeignScan = blackholeReScanForeignScan;
fdwroutine->EndForeignScan = blackholeEndForeignScan;
/* remainder are optional - use NULL if not required */
/* support for insert / update / delete */
fdwroutine->AddForeignUpdateTargets = blackholeAddForeignUpdateTargets;
fdwroutine->PlanForeignModify = blackholePlanForeignModify;
fdwroutine->BeginForeignModify = blackholeBeginForeignModify;
fdwroutine->ExecForeignInsert = blackholeExecForeignInsert;
fdwroutine->ExecForeignUpdate = blackholeExecForeignUpdate;
fdwroutine->ExecForeignDelete = blackholeExecForeignDelete;
fdwroutine->EndForeignModify = blackholeEndForeignModify;
/* support for EXPLAIN */
fdwroutine->ExplainForeignScan = blackholeExplainForeignScan;
fdwroutine->ExplainForeignModify = blackholeExplainForeignModify;
/* support for ANALYSE */
fdwroutine->AnalyzeForeignTable = blackholeAnalyzeForeignTable;
PG_RETURN_POINTER(fdwroutine);
}

Future
●

Even more Wrappers

●

Check Constraints on Foreign Tables
–

●

Allows partitioning

Joins
–

Custom Scan API
●

Probably will not be the way to do this, but progress being made

Questions?
jimm@openscg.com
@jim_mlodgenski

Postgresql Federation

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