Streaming replication

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2016-10-29PostgreSQL streaming replication sobre VPN

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RDBMS =

Relational

Data

Base

Management

SystemManejador de bases de datos

relacionales

ACID =

Atomicity

Consistency

Isolation

Durability

http://en.wikipedia.org/wiki/ACID



WAL =Write

Ahead

Log

https://www.postgresql.org/docs/9.6/static/wal-intro.html



#------------------------------------------------------------------------------# RESOURCE USAGE (except WAL)#------------------------------------------------------------------------------

# - Memory -

shared_buffers = 512MB! ! ! # min 128kB! ! ! ! ! # (change requires restart)temp_buffers = 32MB! ! ! # min 800kB#max_prepared_transactions = 0! ! # zero disables the feature! ! ! ! ! # (change requires restart)

postgresql.conf



Shared Buffers

SELECT * FROM dbmail_users;



Shared Buffers

SELECT * FROM dbmail_users ORDER BY user_idnr DESC LIMIT 5;



Shared Buffers

INSERT INTO dbmail_users (user_idnr, userid) VALUES (31337, ‘sandino’);



Shared Buffers

COMMIT;



Shared Buffers

INSERT INTO dbmail_users (user_idnr, userid) VALUES (31338, ‘chalo’);INSERT INTO dbmail_users (user_idnr, userid) VALUES (31339, ‘roa’);



Shared Buffers

COMMIT;



Shared Buffers

UPDATE dbmail_users SET userid = ‘[email protected]’ WHERE user_idnr = 31337;





Shared Buffers

UPDATE dbmail_users SET userid = ‘[email protected]’ WHERE user_idnr = 31338;UPDATE dbmail_users SET userid = ‘[email protected]’ WHERE user_idnr = 31339;







Shared Buffers

ROLLBACK;



Shared Buffers






Shared Buffers

COMMIT;



Shared Buffers

VACUUM;



#------------------------------------------------------------------------------# WRITE AHEAD LOG#------------------------------------------------------------------------------

# - Settings -

wal_level = hot_standby # minimal, archive, or hot_standby # (change requires restart)#fsync = on # turns forced synchronization on or off

postgresql.conf



wal_buffers = 16MB # min 32kB, -1 sets based on shared_buffers # (change requires restart)#wal_writer_delay = 200ms # 1-10000 milliseconds

#commit_delay = 0 # range 0-100000, in microseconds#commit_siblings = 5 # range 1-1000

postgresql.conf



Shared Buffers + WAL

INSERT INTO dbmail_users (user_idnr, userid) VALUES (31337, ‘sandino’);

DB WAL



COMMIT;


DB WAL



INSERT INTO dbmail_users (user_idnr, userid) VALUES (31338, ‘chalo’);INSERT INTO dbmail_users (user_idnr, userid) VALUES (31339, ‘roa’);


DB WAL



COMMIT;


DB WAL





DB WAL





CHECKPOINT


DB WAL



ROLLBACK;


DB WAL





DB WAL





COMMIT;


DB WAL



... En algún punto del tiempo ....


DB WAL



Respaldo baseSELECT pg_start_backup('label');

rsync -vacHz --progress /var/lib/pgsql/data/ \ [email protected]:/var/lib/pgsql/data/

SELECT pg_stop_backup();

rsync -vacHz --progress /var/lib/pgsql/archive/ \ [email protected]:/var/lib/pgsql/archive/







recovery.conf

# Specifies a command to load archive segments from the WAL archive. If# wal_keep_segments is a high enough number to retain the WAL segments# required for the standby server, this may not be necessary. But# a large workload can cause segments to be recycled before the standby# is fully synchronized, requiring you to start again from a new base backup.restore_command = 'cp /path_to/archive/%f "%p"'



COMMIT;

Respaldo incremental

DB WAL

DB WAL

COMMIT;

Recuperación

DB WAL

COMMIT;

log shipping

DB WAL

DB WAL

recovery.conf para streaming replication

# Specifies whether to start the server as a standby. In streaming replication,# this parameter must to be set to on.standby_mode = 'on'# Specifies a connection string which is used for the standby server to connect# with the primary.primary_conninfo = 'host=192.168.0.10 port=5432 user=replicator'# Specifies a trigger file whose presence should cause streaming replication to# end (i.e., failover).trigger_file = '/var/lib/pgsql/trigger'

restore_command = 'cp /var/lib/pgsql/archive/%f "%p"'



COMMIT;

Streaming replication

DB WAL

DB WAL

Configuración origen

$ vi postgresql.conf

listen_addresses = '192.168.0.10'

$ vi pg_hba.conf

# The standby server must connect with a user that has replication privileges.host replication replication 192.168.0.20/22 trust

http://wiki.postgresql.org/wiki/Streaming_Replication


wal_level = hot_standby

max_wal_senders = 5

wal_keep_segments = 32

archive_mode = onarchive_command = 'cp %p /path_to/archive/%f'



$ psql -c "SELECT pg_start_backup('label', true)"$ rsync -ac ${PGDATA}/ standby:/srv/pgsql/standby/ --exclude postmaster.pid$ psql -c "SELECT pg_stop_backup()"




hot_standby = on


Configuración destino

$ vi recovery.conf

standby_mode = 'on'

primary_conninfo = 'host=192.168.0.10 port=5432 user=postgres'

trigger_file = '/path_to/trigger'

restore_command = 'cp /path_to/archive/%f "%p"'



$ psql -c "SELECT pg_current_xlog_location()" -h192.168.0.10 (primary host) pg_current_xlog_location -------------------------- 0/2000000(1 row)

$ psql -c "select pg_last_xlog_receive_location()" -h192.168.0.20 (standby host) pg_last_xlog_receive_location ------------------------------- 0/2000000(1 row)

$ psql -c "select pg_last_xlog_replay_location()" -h192.168.0.20 (standby host) pg_last_xlog_replay_location ------------------------------ 0/2000000(1 row)


Verificación

# The displayed LSNs indicate the byte position that the standby server has# written up to in the xlogs.[primary] $ ps -ef | grep senderpostgres 6879 6831 0 10:31 ? 00:00:00 postgres: wal sender process postgres 127.0.0.1(44663) streaming 0/2000000

[standby] $ ps -ef | grep receiverpostgres 6878 6872 1 10:31 ? 00:00:01 postgres: wal receiver process streaming 0/2000000


Verificación

Problemática

Estrecho de banda (100 Mbps)

Latencia (200 ms)

Rotación de WAL segments

Downtime (48+ horas)

COMMIT;

Log archiving + streaming replication

DB WAL

DB

WAL

Archive

# - Archiving -

archive_mode = on # enables archiving; off, on, or always # (change requires restart)archive_command = 'scp "%p" archive.example.com:/archive/"%f"'



standby_mode = 'on'

primary_conninfo = 'host=192.168.0.10 port=5432 user=postgres'

trigger_file = '/data/pgsql/trigger'

restore_command = 'scp archive.example.com:/archive/"%f" "%p"'



Referencias


https://www.postgresql.org/docs/9.6/static/wal-intro.htmlhttps://www.postgresql.org/docs/9.6/static/warm-standby.html

https://www.postgresql.org/docs/9.6/static/continuous-archiving.htmlhttp://en.wikipedia.org/wiki/Relational_database_management_system


Sandino Araico Sánchez <[email protected]>@KBrown

#mendozaaaa



https://www.postgresql.org/docs/9.6/static/continuous-archiving.html

https://www.postgresql.org/docs/9.6/static/continuous-archiving.html

http://en.wikipedia.org/wiki/Relational_database_management_system

http://en.wikipedia.org/wiki/Relational_database_management_system



Streaming replication

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