Configuring replication between two databases is considered to be the best strategy towards achieving high availability during disasters and provides fault tolerance against unexpected failures. PostgreSQL satisfies this requirement through streaming replication. We shall talk about another option called logical replication and logical decoding in our future blog post. Streaming replication in PostgreSQL works on log shipping.
Every transaction in postgres is written to a transaction log called WAL write-ahead log to achieve durability. A slave uses these WAL segments to continuously replicate changes from its master.
And then the streaming replication begins. Create the user in master using whichever slave should connect for streaming the WALs. The following parameters on the master are considered as mandatory when setting up streaming replication. You can get the location of postgresql. The IP address mentioned in this line must match the IP address of your slave server. Please change the IP accordingly. You can also take a tar format backup from master and copy that to the slave server.
The following step can be used to stream data directory from master to slave. This step can be performed on a slave. In the above command, you see an optional argument -R. When you pass -R, it automatically creates a recovery. It is mandatory to create the recovery.
If you are not using the backup type mentioned above, and choose to take a tar format backup on master that can be copied to slave, you must create this recovery. Here are the contents of the recovery. This recovery. If you have configured a backup remotely using the streaming method mentioned in Step 4 , it just copies all the files and directories to the data directory of the slave.
Which means it is both a back up of the master data directory and also provides for restore in a single step. Once done, you may proceed to start your PostgreSQL instance on the slave using the following command. This parameter takes a shell command or a script that can be used to fetch the WAL needed by a slave if the WAL is not available on the master.
To achieve that, you have to add a line similar to the next example to your recovery.
Check for these processes on both master and slave using the following commands. You must see those all three processes running on master and slave as you see in the following example log.
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Avinash Vallarapu. Avinash Vallarapu joined Percona in the month of May He has given several talks and trainings on PostgreSQL. WAL shipping is not strictly needed for streaming replication.
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In this step, we will configure the 'master server' with IP address ' In the archive section line and , turn on the archiving option and add the archiving command. In the replication section line and , change the value to the max number of WAL sender process. Now create a new directory inside of the 'main' directory for the archive configuration - run the command below as postgres user:.
Configure the slave server like the master server. Use su to become the postgres user and go to the PostgreSQL configuration directory.
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Go to the master server and log into the postgres user, then run the command below to see the replication info. Next, test to create a new database from the master server and then check that the database exist on the slave server. Now login to the slave server and check that the 'howtoforge' database has been mirrored to the slave server automatically. I have installed postgresql with active-passive with above steps in redhat 7. Please help me in installing it either both master-slave as write access or share the steps to install postgresql in multi master mode which will be helpful.
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Am I right??? The IP here is master server IP. And I mv.. This feature is only available to subscribers. Get your subscription here. Log in or Sign up.
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