I have a galera cluster of three nodes, If I shut down the the three virtual machines and started them all at once, systemd will automatically start mariadb on each of the virtual machines.
Some times it happens that all of the mariadb instances start at once, and this result of a broken cluster.
Which I have to reinitiate using galera_new_cluster
The question is, why does starting all the mariadb instances at once break the cluster ?
Thank you
Whenever you start a node, it either starts as the first node in the cluster (initiates a new cluster), or it attempts to connect to an existing nodes using wsrep_cluster_address. The behavior depends on the node options.
So, every time when you shut down or lose all nodes and start them again, there is nothing to connect to, and you need to start a new cluster. galera_new_cluster does that by starting a node with --wsrep-new-cluster option which overrides the current value of wsrep_cluster_address.
If sometimes it works for you automatically, it most likely means that one of your nodes is permanently configured as the "first node", either via wsrep_cluster_address=gcomm://, or via wsrep-new-cluster. It is a wrong setup in itself. If you lose or shut down only this node and have to restart it, it won't join the remaining nodes in the cluster, it will create a new one.
When you start all nodes at once, you create a race condition. If your "first node" comes up first and initializes quickly enough, it will create a new cluster, and other nodes will join it. If another node comes up first, it won't be able to join anything, thus you get a "broken cluster".
You can find more information on restarting the whole cluster here:
http://galeracluster.com/documentation-webpages/restartingcluster.html
Recommendate way of bootstrapping cluster is to start a advanced node first then second and third so for you need to check lsn no of all nodes or check grastate.date file where you can check all nodes value .
so follow these steps your cluster node will not be crash
Related
I am having problems trying to build a database solution for the experiment to ensure HA and performance(sharding).
Now, I have a spider node and two galera clusters (3 nodes in each cluster), as shown in the figure below, and this configuration works well in general cases.:
However, as far as I know, when the spider engine performs sharding, it must assign primary IP to distribute SQL statements to two nodes in different Galera clusters.
So my first question here is:
Q1): When the machine .12 shuts down due to destruction, how can I make .13 or .14(one of them) automatically replace .12?
The servers that spider engine know
Q2): Are there any open source tools (or technologies) that can help me deal with this situation? If so, please explain how it works. (Maybe MaxScale? But I never knew what it is and what it can do.)
Q3): The motivation for this experiment is as follows. An automated factory has many machines, and each machine generates some data that must be recorded during the production process (maybe hundreds or thousands of data per second) to observe the operation of the machine and make the quality of each batch of products the best.
So my question is: how about this architecture (Figure 1)? or please provides your suggestions.
You could use MaxScale in front of the Galera cluster to make the individual nodes appear like a combined cluster. This way Spider will be able to seamlessly access the shard even if one of the nodes fails. You can take a look at the MaxScale tutorial for instructions on how to configure it for a Galera cluster.
Something like this should work:
This of course has the same limitation that a single database node has: if the MaxScale server goes down, you'll have to switch to a different MaxScale for that cluster. The benefit of using MaxScale is that it is in some sense stateless which means it can be started and stopped almost instantly. A network load balancer (e.g. ELB) can already provide some form of protection from this problem.
I have a Mariadb Galera cluster with 2 nodes and it is up and running.
Before moving to production, I want to make sure that if a node crashes abruptly, It should come up on its own.
I tried using systemd "restart", but after killing the mysql process the mariadb service does not come up, so, is there any tool or method, that I can use to automate bringing up the nodes after crashes?
Galera clusters needs to have quorum (3 nodes).
In order to avoid a split-brain condition, the minimum recommended number of nodes in a cluster is 3. Blocking state transfer is yet another reason to require a minimum of 3 nodes in order to enjoy service availability in case one of the members fails and needs to be restarted. While two of the members will be engaged in state transfer, the remaining member(s) will be able to keep on serving client requests.
You can read more here.
I'm running into an issue with the way Galera cluster is set up to work with MariaDB.
Each node in the cluster has to have a configuration that houses the IP addresses of every other node (inclusive) in the cluster. If I ever want to add a node to the cluster, I have to manually add that node's IP address to the configurations on every other node.
This makes spinning up and down servers dynamically for the cluster difficult.
Are there any work arounds for this? Possibly a way to notify every node of a new node being added to the cluster remotely?
Galera clusters only need one server working as a master node. You can use any or all of the servers in the cluster as the cluster address for the new node and the new node will automatically connect to the rest of the nodes.
Example
Active Cluster:
10.0.0.2 (the first node of the galera cluster)
10.0.0.3
10.0.0.4
If we want to add 10.0.0.5 to the cluster, we can use any of the following as a cluster address for it:
gcomm://10.0.0.2
gcomm://10.0.0.3
gcomm://10.0.0.4
gcomm://10.0.0.2,10.0.0.3
gcomm://10.0.0.2,10.0.0.4
gcomm://10.0.0.3,10.0.0.4
gcomm://10.0.0.2,10.0.0.3,10.0.0.4
The down side to this is that the new node would lose the other servers as fall back if the ones that they have configured in their cluster address are down.
So a work around for this is to have X number of static nodes that will never go down, then use all of those as the cluster addresses for any new slaves that you bring up.
Suppose that we have two application servers(app1 and app2) and also we setup multi master MariaDB clustering with two nodes(node1 and node2) without any HAProxy.Can we connect app1 to node1 and app2 to node2 and also both of app1 and app2 write to node1 and node2?
Does it cause any conflict?
Galera solves most of the problems that occur with Master-Master:
If one of Master-Master dies, now what? Galera recovers from any of its 3 nodes failing.
If you INSERT the same UNIQUE key value in more than one Master, M-M hangs; Galera complains to the last client to COMMIT.
If a node dies and recovers, the data is automatically repaired.
You can add a node without manually doing the dump, etc.
etc.
However, there are a few things that need to be done differently to when using Galera: Tips
I have two MariaDB Galera Cluster with 3 nodes.
Cluster 1 : MDB-01,MDB-02,MDB-03
Cluster 2 : MDBDR-01,MDBDR-02,MDBDR-03
These two clusters are in two different data centers which are in two geographical regions.
Cluster 1 is PRODUCTION cluster and Cluster 2 is DR cluster
Asynchronous replication using GTID has been setup between MDB-01 to MDBDR-01
as per given configuration in the link :
http://www.severalnines.com/blog/deploy-asynchronous-replication-slave-mariadb-galera-cluster-gtid-clustercontrol
(Link is asynchronous replication between MariaDB Galera Cluster to Stand alone MariaDB instance.
However I have setup same configuration for asynchronous replication between MariaDB Galera Cluster to MariaDB Galera Cluster)
I am able to switch from current slave MDBDR-01 => MDB-01 to MDBDR-01 => MDB-02 with below command :
CHANGE MASTER TO master_host='MDB-02'
However I am getting challenge how to point MDBDR-02 => MDB-01 in case of MDBDR-01 is down.
Could you please provide inputs to achieve pointing MDBDR-02 => MDB-01 or MDBDR-03 => MDB-01.
One thing you need to understand, that article briefly mentions, is that each MariaDB's GTID implementation can cause problems in this situation. Since each node maintains its own list of GTIDs and galera transactions do not have their own id, it is possible that the same GTID does not point to the same place on each server (see this article).
Due to that problem, I wouldn't attempt what you're doing without MariaDB 10.1. MariaDB 10.1.8 was just released and is the first GA release of the 10.1 line. 10.1 changes the GTID implementation so galera transactions use their own server_id (set via a config variable). You can then filter replication on the slaves to only replicate the galera id.
To switch to a different slave server, you will need to get that last GTID executed on the old slave. The gtid_slave_pos is stored in mysql.gtid_slave_pos, but mysql.* tables are not replicated. I'm not completely sure and I don't have a way of testing if the original GTID of a transaction is passed to the other slave galera nodes (i.e. if the master cluster's galera server_id is 1 and the slave cluster's galera server_id is 2 and MDBDR-01 gets a slave event with GTID 1-1-123, will MDBDR-02 log it as 1-1-123 or 1-2-456). I'm guessing that it doesn't since the new GTID implementation should change the server_id, but you may be able to verify this. Since you probably can't get the last executed master GTID from a different slave galera node, you will probably need to get the GTID from the old slave which may not be possible unless you gracefully shut down the old slave. You may need to find the GTID from the last executed transaction in the binlog on the new slave and try to match that to a transaction in the master's binlog. Also, if you're not using sync_binlog = 1, the binlog is not reliable and might be a bit behind.
Since each galera slave node probably doesn't know about the executed GTIDs and can't skip previous GTID events, you may also have to play with SQL_SLAVE_SKIP_COUNTER to get to the correct position if the GTID you found is behind.
When you get the GTID (or a guess of it) you will then set up replication on the new slave the same way you set it up on the original slave. The following commands should do it:
SET GLOBAL gtid_slave_pos = "{Last Executed GTID}";
CHANGE MASTER TO master_host="{Master Address}", master_port={Master Port}, master_user="{Replication User}", master_password={Replication Password}, master_use_gtid=slave_pos;
START SLAVE;
You should also disable replication on the old slave before restarting it so the missed events don't get replicated twice.
Until the executed slave GTID is replicated through galera, which might never happen, failover like this will be a messy process.