Step 6 - Checking the cluster v5

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Checking the cluster

With the cluster up and running, it is worthwhile running some basic checks on how effectively it is replicating.

In the following example, we show one quick way to do this but you should ensure that any testing you perform is appropriate for your use case.

  • Preparation
    • Ensure the cluster is ready
      • Log into the database on host-one/node-one
      • Run select bdr.wait_slot_confirm_lsn(NULL, NULL);
      • When the query returns the cluster is ready
  • Create data The simplest way to test the cluster is replicating is to log into one node, create a table and populate it.
    • On node-one create a table
      CREATE TABLE quicktest ( id SERIAL PRIMARY KEY, value INT );
    • On node-one populate the table
      INSERT INTO quicktest (value) SELECT random()*10000 FROM generate_series(1,10000);
    • On node-one monitor performance
      select * from bdr.node_replication_rates;
    • On node-one get a sum of the value column (for checking)
      select COUNT(*),SUM(value) from quicktest;
  • Check data
    • Log into node-two
      Log into the database on host-two/node-two
    • On node-two get a sum of the value column (for checking)
      select COUNT(*),SUM(value) from quicktest;
    • Compare with the result from node-one
    • Log into node-three Log into the database on host-three/node-three
    • On node-three get a sum of the value column (for checking)
      select COUNT(*),SUM(value) from quicktest;
    • Compare with the result from node-one and node-two

Worked example

Preparation

Log into host-one's Postgres server.

ssh admin@host-one
sudo -iu enterprisedb psql bdrdb

This is your connection to PGD's node-one.

Ensure the cluster is ready

To ensure that the cluster is ready to go, run: 

select bdr.wait_slot_confirm_lsn(NULL, NULL)

This query will block while the cluster is busy initializing and return when the cluster is ready.

In another window, log into host-two's Postgres server

ssh admin@host-two
sudo -iu enterprisedb psql bdrdb

Create data

On node-one create a table

Run

CREATE TABLE quicktest ( id SERIAL PRIMARY KEY, value INT );

On node-one populate the table

INSERT INTO quicktest (value) SELECT random()*10000 FROM generate_series(1,10000);

This will generate a table of 10000 rows of random values.

On node-one monitor performance

As soon as possible, run:

select * from bdr.node_replication_rates;

And you should see statistics on how quickly that data has been replicated to the other two nodes.

bdrdb=# select * from bdr.node_replication_rates;
 peer_node_id | target_name | sent_lsn  | replay_lsn | replay_lag | replay_lag_bytes | replay_lag_size | apply_rate | catchup_interv
al
--------------+-------------+-----------+------------+------------+------------------+-----------------+------------+---------------
---
   1954860017 | node-three  | 0/DDAA908 | 0/DDAA908  | 00:00:00   |                0 | 0 bytes         |      13682 | 00:00:00
   2299992455 | node-two    | 0/DDAA908 | 0/DDAA908  | 00:00:00   |                0 | 0 bytes         |      13763 | 00:00:00
(2 rows)

And it's already replicated.

On node-one get a checksum

Run:

select COUNT(*),SUM(value) from quicktest;

to get some values from the generated data:

bdrdb=# select COUNT(*),SUM(value) from quicktest;
Output
 count  |    sum
--------+-----------
 100000 | 498884606
(1 row)

Check data

Log into host-two's Postgres server.

ssh admin@host-two
sudo -iu enterprisedb psql bdrdb

This is your connection to PGD's node-two.

On node-two get a checksum

Run:

select COUNT(*),SUM(value) from quicktest;

to get node-two's values for the generated data:

bdrdb=# select COUNT(*),SUM(value) from quicktest;
Output
 count  |    sum
--------+-----------
 100000 | 498884606
(1 row)

Compare with the result from node-one

And the values will be identical.

You can repeat the process with node-three, or generate new data on any node and see it replicate to the other nodes.

Log into host-threes's Postgres server.

ssh admin@host-two
sudo -iu enterprisedb psql bdrdb

This is your connection to PGD's node-three.

On node-three get a checksum

Run:

select COUNT(*),SUM(value) from quicktest;

to get node-three's values for the generated data:

bdrdb=# select COUNT(*),SUM(value) from quicktest;
Output
 count  |    sum
--------+-----------
 100000 | 498884606
(1 row)

Compare with the result from node-one and node-two

And the values will be identical.

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