rc9000 / postgres-ha-sandbox

Postgres 10 HA Sandbox

Intro

• This repository provides a vagrant-based pre-made postgresql 10 streaming replication, hot-standby two node cluster for your own high-availability experiments
• It is based on the very well-written guide in https://blog.raveland.org/post/postgresql_sr/
• For a complete overview of postgres HA options, visit https://www.postgresql.org/docs/10/static/high-availability.html
• The Vagrantfile will launch two nodes, pglcuster01 (Master) and pgcluster02 (Slave)

Sample Database

• The cluster will be loaded with the pgfoundry dellstore2 sample database, available from http://pgfoundry.org/frs/?group_id=1000150&release_id=376
• to connect, vagrant ssh pgcluster01 then sudo -i -u postgres psql dellstore2

Verifiy

Updates to the master should show up in little time on the slave. Execute e.g.:

postgres@pgcluster01:~$ psql dellstore2 -c "update products set title = 'MY_NEW_TITLE' where prod_id = 1"
UPDATE 1

And verify shortly after with:

postgres@pgcluster02:~$  psql dellstore2 -c 'select * from products where prod_id = 1'
 prod_id | category |    title     |      actor       | price | special | common_prod_id 
---------+----------+--------------+------------------+-------+---------+----------------
       1 |       14 | MY_NEW_TITLE | PENELOPE GUINESS | 25.99 |       0 |           1976

Troubleshooting

Identifier Mismatch

The master and slave need to match up, ie. slave needs to originate from pg_basebackup. If it isn't the system identifiers don't match up and the slave refuses to start:

2018-06-09 21:17:55.172 UTC [2104] FATAL:  database system identifier differs between the primary and standby
2018-06-09 21:17:55.172 UTC [2104] DETAIL:  The primary's identifier is 6565195479380034189, the standby's identifier is 6564997952538579566.

These identifiers are randomly chosen at DB creation time

basebackup notes

The -D option designates the local directory, the whole remote cluster will be restored to this location.

Verification

postgres@pgcluster01:~$ psql dellstore2 -c "update products set title = 'XXXX' where prod_id = 1"

postgres@pgcluster02:~$ psql dellstore2 -c 'select * from products where prod_id = 1'
 prod_id | category | title |      actor       | price | special | common_prod_id 
---------+----------+-------+------------------+-------+---------+----------------
       1 |       14 | XXXX  | PENELOPE GUINESS | 25.99 |       0 |           1976
(1 row)

Todo

• document failover
• document failback