plProxy, pgBouncer, pgBalancer

plProxy, pgBouncer,
pgBalancer
Asko Oja

Vertical Split
 All database access through functions requirement from the start
 Moved out functionality into separate servers and databases as load increased.
 Slony for replication, plpython for remote calls.
 As number of databases grew we ran into problems
 Slony replication became unmanageable because of listen/notify architecture
and locking.
 We started looking for alternatives that ended up creating SkyTools PgQ and
Londiste.

userdb userdb analysisdb
userdb
shopdb

shopdb shopdb servicedb

Time

Horizontal Split
 One server could not service one table anymore
 We did first split with plpython remote calls
 Replaced it with plProxy language but it had still several problems
 complex configuration database
 internal pooler and complex internal structure
 scaleability issues

userdb userdb
userdb

userdb

userdb_p0 userdb_p2
userdb_p0 userdb_p1 userdb_p2 userdb_p3
userdb_p1 userdb_p3

Time

plProxy Version 2
 plProxy second version
 just remote call language FrontEnd WebServer
 simplified internal structure
 added flexibility
 added features
 configuration and management
userdb
improved
 Connection pooling separated into
pgBouncer. pgBouncer

 Resulting architecture is
 Scaleable
 Maintainable
 Beautiful in it's simplicity :) userdb_p0 userdb_p1

Overall picture

Online databases proxydb proxydb
pgBouncer
● Proxy db's
pgBouncer pgBouncer

● pgBouncers

● OLTP db's

● read only db's userdb_p01 userdb_p01 shopdb shopdb_ro
SkyTools SkyTools SkyTools SkyTools

Support databases
● Queue db's
queuedb
SkyTools
● Datamining

● Batchjobs

● Backoffice

● Greenplum
batchdb analysisdb backofficedb

plProxy: Installation
 Download PL/Proxy from http://pgfoundry.org/projects/plproxy and extract.
 Build PL/Proxy by running make and make install inside of the plproxy directory. If
your having problems make sure that pg_config from the postgresql bin directory is
in your path.
 To install PL/Proxy in a database execute the commands in the plproxy.sql file. For
example psql -f $SHAREDIR/contrib/plproxy.sql mydatabase
 Steps 1 and 2 can be skipped if your installed pl/proxy from a packaging system
such as RPM.
 Create a test function to validate that plProxy is working as expected.

CREATE FUNCTION public.get_user_email(text) RETURNS text AS
$_$ connect 'dbname=userdb'; $_$
LANGUAGE plproxy SECURITY DEFINER;

plProxy Language
 The language is similar to plpgsql - string quoting, comments, semicolon at the
statements end.It contains only 4 statements: CONNECT, CLUSTER, RUN and
SELECT.
 Each function needs to have either CONNECT or pair of CLUSTER + RUN
statements to specify where to run the function.
 CONNECT 'libpq connstr'; -- Specifies exact location where to connect and
execute the query. If several functions have same connstr, they will use same
connection.
 CLUSTER 'cluster_name'; -- Specifies exact cluster name to be run on. The cluster
name will be passed to plproxy.get_cluster_* functions.
 CLUSTER cluster_func(..); -- Cluster name can be dynamically decided upon
proxy function arguments. cluster_func should return text value of final cluster
name.

plProxy Language RUN ON ...
 RUN ON ALL; -- Query will be run on all partitions in cluster in parallel.
 RUN ON ANY; -- Query will be run on random partition.
 RUN ON <NR>; -- Run on partition number <NR>.
 RUN ON partition_func(..); -- Run partition_func() which should return one or more
hash values. (int4) Query will be run on tagged partitions. If more than one partition
was tagged, query will be sent in parallel to them.

$_$
cluster 'userdb';
run on public.get_hash($1);
$_$
LANGUAGE plproxy SECURITY DEFINER;

plProxy Configuration
 Schema plproxy and 3 functions are needed for plProxy
 plproxy.get_cluster_partitions(cluster_name text) – initializes
plProxy connect strings to remote databases
 plproxy.get_cluster_version(cluster_name text) – used by plProxy to
determine if configuration has changed and should be read again. Should be as fast
as possible because it is called for every function call that goes through plProxy.
 plproxy.get_cluster_config(in cluster_name text, out key text,
out val text) – can be used to change plProxy parameters like connection
lifetime.
CREATE FUNCTION plproxy.get_cluster_version(i_cluster text)
RETURNS integer AS $$
SELECT 1;
$$ LANGUAGE sql SECURITY DEFINER;

CREATE FUNCTION plproxy.get_cluster_config(
cluster_name text, OUT "key" text, OUT val text)
RETURNS SETOF record AS $$
SELECT 'connection_lifetime'::text as key, text( 30*60 ) as val;
$$ LANGUAGE sql;

plProxy: Get Cluster Partitions
CREATE FUNCTION plproxy.get_cluster_partitions(cluster_name text)
RETURNS SETOF text AS $$
begin
if cluster_name = 'userdb' then
return next 'port=9000 dbname=userdb_p00 user=proxy';
return next 'port=9000 dbname=userdb_p01 user=proxy';
return;
end if;
raise exception 'no such cluster: %', cluster_name;
end; $$ LANGUAGE plpgsql SECURITY DEFINER;

CREATE FUNCTION plproxy.get_cluster_partitions(i_cluster_name text)
RETURNS SETOF text AS $$
declare
r record;
begin
for r in
select connect_string
from plproxy.conf
where cluster_name = i_cluster_name
loop
return next r.connect_string;
end loop;
if not found then
raise exception 'no such cluster: %', i_cluster_name;
end if;
return;
end; $$ LANGUAGE plpgsql SECURITY DEFINER;

plProxy: Remote Calls
 We use remote calls mostly for read only queries in cases where it is not reasonable
to replicate data needed to calling database.
 For example balance data is changing very often but whenever doing decisions
based on balance we must use the latest balance so we use remote call to get user
balance.
 Another use case when occasionally archived data is needed together with online
data.

userDB
get_email

shopDB balanceDB
get_balance

archiveDB
get_old_orders

plProxy: Remote Calls (update)
 plProxy remote calls inside transactions that change data in remote database
should have special handling
 no 2 phase commit
 some mechanism should be used to handle possible problems like inserting events
into PgQ queue and let consumer validate that transaction was committed or rolled
back and act accordingly.

balanceDB
change_balance
shopDB
balance
events

balance
change
handler

plProxy: Proxy Databases
 Additional layer between application and databases.
 Keep applications database connectivity simpler giving DBA's and developer's more
flexibility for moving data and functionality around.
 Security layer. By giving access to proxy database DBA's can be sure that user has
no way of accessing tables by accident or by any other means as only functions
published in proxy database are visible to user.

BackOffice
Application

manualfixDb backofficeDb
(proxy) (proxy)

shopDb userDB internalDb

plProxy: Run On All CREATE FUNCTION stats._get_stats(
OUT stat_name text,
OUT stat_value bigint
 Run on all executes ) RETURNS SETOF record AS
query on all partitions in $_$
cluster once. Partitions cluster 'userdb';
are identified by connect run on all;
$_$
strings. LANGUAGE plproxy SECURITY DEFINER;
 Useful for gathering stats
CREATE FUNCTION stats.get_stats(
from several databases OUT stat_name text,
or database partitions. OUT stat_value bigint
) RETURNS SETOF record AS
 Also usable when exact $_$
partition where data select stat_name
resides is not known. , (sum(stat_value))::bigint
Then function may be run from stats._get_stats()
group by stat_name
on all partitions and only order by stat_name;
the one that has data $_$
does something. LANGUAGE sql SECURITY DEFINER;

plProxy: Geographical
 plProxy can be used to split database into partitions based on country code.
Example database is split into 'us' and 'row' (rest of the world)
 Each function call caused by online users has country code as one of the
parameters
 All data is replicated into internal database for use by internal applications and batch
jobs. That also reduces number of indexes needed in online databases.

CREATE FUNCTION public.get_cluster(
i_key_cc text
onlinedb
) RETURNS text AS (proxy)
$_$
BEGIN
IF i_key_cc = 'us' THEN
RETURN 'oltp_us';
ELSE onlinedb_US onlinedb_ROW backenddb
RETURN 'oltp_row';
END IF;
END;
$_$ LANGUAGE plpgsql;

plProxy: Partitioning Proxy Functions
 We have partitioned most of our database by username using PostgreSQL hashtext
function to get equal distribution between partitions.
 When splitting databases we usually prepare new partitions in other servers and
then switch all traffic at once to keep our life pleasant.
 Multiple exact copies of proxy database are in use for scaleability and availability
considerations.
$_$
cluster 'userdb';
run on public.get_hash($1);
$_$ LANGUAGE plproxy SECURITY DEFINER;

CREATE FUNCTION public.get_hash(i_user text) RETURNS integer AS
$_$
BEGIN
return hashtext(lower(i_user));
END;
$_$ LANGUAGE plpgsql SECURITY DEFINER;

plProxy: Partitioning Partition Functions
 Couple of functions in partconf schema added to each partition:
 partconf.global_id() - gives globally unique keys
 partconf.check_hash() - checks that function call is in right partition
 partconf.valid_hash() - used as trigger function
CREATE FUNCTION public.get_user_email(i_username text) RETURNS text AS
$_$
DECLARE
retval text;
BEGIN
PERFORM partconf.check_hash(lower(i_username));

SELECT email
FROM users
WHERE username = lower(i_username)
INTO retval;

RETURN retval;
END;
$_$ LANGUAGE plpgsql SECURITY DEFINER;

plProxy: Summary
 plProxy adds 1-10ms overhead when used together with pgBouncer.
 Quote from Gavin M. Roy's blog “After closely watching machine stats for the first 30
minutes of production, it appears that plProxy has very little if any impact on
machine resources in our infrastructure.”
 On the other hand plProxy adds complexity to development and maintenance so it
must be used with care but that is true for most everything.
 Our largest cluster is currently running in 16 partitions on 16 servers.

pgBouncer
 pgBouncer is lightweight and robust connection pooler
for Postgres.
Applications
 Low memory requirements (2k per connection by
default). This is due to the fact that PgBouncer does not
need to see full packet at once. thousands of
 It is not tied to one backend server, the destination connections
databases can reside on different hosts.
 Supports pausing activity on all or only selected pgBouncer
databases.
 Supports online reconfiguration for most of the settings.
tens of
 Supports online restart/upgrade without dropping client connections
connections.
 Supports protocol V3 only, so backend version must be
>= 7.4. Database

 Does not parse SQL so is very fast and uses little CPU
time.

pgBouncer Pooling Modes
 Session pooling - Most polite method. When client connects, a server connection
will be assigned to it for the whole duration it stays connected. When client
disconnects, the server connection will be put back into pool. Should be used with
legacy applications that won't work with more efficient pooling modes.
 Transaction pooling - Server connection is assigned to client only during a
transaction. When PgBouncer notices that transaction is over, the server will be put
back into pool. This is a hack as it breaks application expectations of backend
connection. You can use it only when application cooperates with such usage by not
using features that can break.
 Statement pooling - Most aggressive method. This is transaction pooling with a
twist - multi-statement transactions are disallowed. This is meant to enforce
"autocommit" mode on client, mostly targeted for PL/Proxy.

pgBouncer Pictures
 http://www.last.fm/user/Russ/journal/2008/02/21/654597/
 Nice blog about pgBouncer

pgBalancer
 Keep pgBouncer small stable and
client1
focused
clientN
 pgBalancer is experiment with
existing software to implement
statement level load balancing.
 So we created sample configuration
using existing software that shows lvs keepalived lvs
how load could be divided on several (master) daemon (slave)
read only databases.
 LVS – Linux Virtual Server is used (
http://www.linuxvirtualserver.org/)
 Different load balancing
algorithms
 Weights on resources.
pgBouncer pgBouncer
shopdb_ro1 shopdb_ro2

SODI Framework Application layer
- java / php ...
 Rapid application development - UI logic
. mostly generated
 Cheap changes - sodi framework
 Most of the design is in metadata.
 Application design stays in sync with
application over time. AppServer layer:
 Minimizes number of database - java / php( ...
roundtrips. - user authentication
- roles rights
 Can send multiple recordsets to one - no business logic
function call.
 Can receive several recordsets from
function call. Database layer
- business logic
- plPython
- PostgreSQL
- SkyTools

President
 President configuration management
application
President President  Java Client allows updates Web
Java RW Web RO
client view only access. All outside
access to system over HTTPS and
personal certificates can be
generated if needed.
Host  Kuberner polls confdb periodically for
Apache
- Harvester commands and executes received
PHP
- Discovery commands.
 Harvester runs inside each host and
writes machine hardware information
into file for Kuberner to read
 Discovery plugin collects specific
ConfDB
configuration files and stores them
Kuberner into ConfDB
 Kuberner: File upload plugin uploads
new configuration files into hosts.

SkyTools
 SkyTools - Python scripting framework and collection of useful database scripts.
Most of our internal tools are based on this framework.
 (centralized) logging and exception handling
 database connection handling
 configuration management
 starting and stopping scripts
 Some of scripts provided by SkyTools
 londiste – nice and simple replication tool
 walmgr - wal standby management script
 serial consumer – Script for executing functions based on data in queue
 queue mover – Move events from one queue into another
 queue splitter – Move events from one queue into several queues
 table dispatcher – writes data from queue into partitioned table
 cube dispatcher - writes data from queue into daily tables

SkyTools: Queue Mover
 Moves data from source queue in one database to another queue in other database.
 Used to move events from online databases to queue databases.
 We don't need to keep events in online database in case some consumer fails to
process them.
 Consolidates events if there are several producers as in case of partitioned
databases.

Batch
OLTP queue job
mover
Batch
db
queue
OLTP mover Batch
job

SkyTools: Queue Splitter
 Moves data from source queue in one database to one or more queue's in target
database based on producer. That is another version of queue_mover but it has it's
own benefits.
 Used to move events from online databases to queue databases.
promotional
 Reduces number of dependencies of online databases.
mailer

Producer
welcome_email
Queue:
Producer welcome_email
password_email
Queue:
Queue: password_email
user_events

queue
splitter transactional
mailer

SkyTools: Table Dispatcher
 Has url encoded events as data source and writes them into table on target
database.
 Used to partiton data. For example change log's that need to kept online only shortly
can be written to daily tables and then dropped as they become irrelevant.
 Also allows to select which columns have to be written into target database
 Creates target tables according to configuration file as needed

table Table: history
dispatcher history_2007_01
history_2007_02
Queue: ...
call_records
table
dispatcher Tabel: cr
cr_2007_01_01
cr_2007_01_02
...

SkyTools: Cube Dispatcher
 Has url encoded events as data source and writes them into partitoned tables in
target database. Logutriga is used to create events.
 Used to provide batches of data for business intelligence and data cubes.
 Only one instance of each record is stored. For example if record is created and
then updated twice only latest version of record stays in that days table.
 Does not support deletes.

Producer Tabel: invoices Tabel: payments
send_welcome_email
invoices
invoices_2007_01_01 payments_2007_01_01
invoices_2007_01_02 payments_2007_01_02
Producer
payments ... ...

Queue:
cube_events cube
dispatcher

Questions, Problems?
 Use SkyTools, plProxy and pgBouncer mailing list at PgFoundry
 skype me: askoja

plProxy, pgBouncer, pgBalancer

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