Now i'm find and config mariadb galera cluster? But i don't know why mariadb galera cluster only support InnoDB.
Pls advice to fix it.
Thanks alots
There is essentially no reason to support any engine other than InnoDB. You can have MyISAM or MEMORY tables, but not get the synchronized replication to the other nodes.
Only with InnoDB, can the synchronous replication be achieved. I feel certain that MyISAM and MEMORY will never be fully supported. However, other transaction-safe engines (Tokudb?) might some day.
Why do you want some other engine? Perhaps we can help you achieve the real goal by some other means.
Addenda...
Synchronous replication, the way Galera implemented, requires being able to ROLLBACK even at COMMIT. Otherwise, duplicate keys would be an unsolvable problem when allowing writes to all nodes.
An aside... NDB takes a radically different approach -- "eventual consistency", wherein duplicate keys can get into the system, but the user has to provide an algorithm for fixing the mess.
InnoDB on a single machine checks as the statements within the transaction are being performed. Galera does not. It is "optimistic" -- transactions are performed without checking the other nodes until the COMMIT. This provided performance because of only a single roundtrip to each other node. (Hence, "medium sized" transactions are optimal.)
MyISAM has no way to do ROLLBACK; it depends on locking table up front. Locking tables on another node would be very clumsy and inefficient.
Galera can work efficiently even in a WAN -- again because of the single action at COMMIT.
Related
The situation is simple: I have a Galera Cluster with two nodes.
I create a new database from a .SQL archive (obtained via mysqldump) in one node. The database is quite big: more or less 500 GB. The other node begins the synchronization but it always stops when the database has reached the same size (4 GB aprox.).
Is there any parameter that limits the process? What can be the problem?
Just if it helps anyone: The problem is related to the database engine. In this case, it was MyIsam and Galera Cluster only works with Innodb.
I'm searching for a high-available SQL solution! One of the articles that I read was about "virtually synchronized" in Galera Cluster: https://www.percona.com/blog/2012/11/20/understanding-multi-node-writing-conflict-metrics-in-percona-xtradb-cluster-and-galera/
He says
When the writeset is actually applied on a given node, any locking
conflicts it detects with open (not-yet-committed) transactions on
that node cause that open transaction to get rolled back.
and
Writesets being applied by replication threads always win
What will happen if the WriteSet conflicts with a committed transaction?
He also says:
Writesets are then “certified” on every node (in order).
How does Galera Cluster make WriteSets ordered over a cluster? Is there any hidden master node who make WriteSets ordered; something like Zookeeper? or what?
This is for the second question (about how Galera orders the writesets).
Galera implements Extended Virtual Synchrony (EVS) based on the Totem protocol. The Totem protocol implements a form of token passing, where only the node with the token is allowed to send out new requests (as I understand it). So the writes are ordered since only one node at a time has the token.
For the academic background, you can look at these:
The Totem Single-Ring Ordering and Membership Protocol
The database state machine and group communication issues
(This Answer does not directly tackle your Question, but it may give you confidence that Galera is 'good'.)
In Galera (PXC, etc), there are two general times when a transaction can fail.
On the node where the transaction is being run, the actions are compared to what is currently running on the same node. If there is a conflict, either one of the transactions is stalled (think innodb_lock_wait_timeout) or is deadlocked (and rolled back).
At COMMIT time, info is sent to all the other nodes; they check your transaction against anything on the node or pending (in gcache). If there is a conflict, a message is sent back saying that there would be trouble. So, the originating node has the COMMIT fail. For this reason, you must check for errors even on the COMMIT statement.
As with single-node systems, a deadlock is usually resolved by replaying the entire transaction.
In the case of autocommit, there is a small, configurable, number of retries, after which the statement will fail. So, again, check for errors. However, since a retry has already been tried, you may want to abort the program.
Currently (in my opinion) Galera, with at least 3 nodes in at least 3 different physical locations, is the best available HA solution for MySQL. It can effectively survive any single-point-of-failure. (Group Replication / InnoDB Cluster, from Oracle, is coming soon, and is very promising.)
One thing to note is that the "critical read" problem has a solution in Galera, but you have to take action. See wsrep_sync_wait. (As of this writing, InnoDB Cluster has no solution.)
See http://mysql.rjweb.org/doc.php/galera for tips (some of which are included above) on coding differences when moving to PXC/Galera.
Currently,I am having mariadb galera cluster operating on two instances of maria db and each node working as Master, replicating data seamlessly. Now, on one node, I want to control one of my database, table etc to not replicate. Can we control the replication behavior to the layer of table, database etc.
By having only 2 nodes on a Galera cluster, you eliminate automatic recovery from a node fault.
By having a db that exists on only one node, you are eliminating the ability to failover by any means.
So, I ask, why use Galera at all?
Back to your question... Galera does not want you to do what you are asking. Maybe there is some letting to let you have MyISAM or MEMORY without replicating it. I don't think you can avoid replicating InnoDB tables.
Currently, i am researching about galera cluster using many of servers(linux centos). Scaling up read traffic is very effective and easy, but scaling for write seems difficult(not improved).
I have used many servers, using maxscale as router(Readconnroute) to distribute write queries in paralles to all servers. But the write speed is not improved.
One option would be to use the Spider storage engine in MariaDB. It supports sharding of tables and should improve write speeds compared to a Galera cluster. On the other hand, you will lose the high availability of the Galera cluster in favor of increased write speeds.
This slide set by Kentoku Shiba on Spider is a good overview of how Spider improves write scalability.
Galera does not improve write speed, as all servers will have to process all writes. MySQL is very poor for scaling writes. You could do it with a proxy (like you mentioned maxscale). Then you can shard your data. You have to pick a key for each table to distribute keys to multiple servers.
I would suggest to use another nosql server i.e. mongodb, which have sharding capabilities built in for write heavy use cases. Mongodb is much easier to set up and to maintain than mysql for this job.
I havea business need related to a MariaDb instance that should work in a master-slave configuration with failover.
Looking at the documentation I have seen that is possible to conigure a multi- cluster-master (galera) or a simple master slave replica.
Any suggestion to configure master-slave + failover?
Many thanks in advance
Roberto
MySQL/MariaDB master-slave replication is great for handling read-heavy workloads. It's also used as a redundancy strategy to improve database availability, and as a backup strategy (i.e. take the snapshot/backup on the slave to avoid interrupting the master). If you don't need a multi-master solution with all the headaches that brings—even with MySQL Cluster or MariaDB Galera Cluster—it's a great option.
It takes some effort to configure. There are several guides out there with conflicting information (e.g. MySQL vs. MariaDB, positional vs. GTID) and several decision points that can affect your implementation (e.g. row vs. statement binlog formats, storage engine selection), and you might have to stitch various pieces together to form your final solution. I've had good luck with MariaDB 10.1 (GTID, row binlog format) and mixed MyISAM and InnoDB storage engines. I create one slave user on the master per slave, and I don't replicate the mysql database. YMMV. This guide is a good starting place, but it doesn't really cover GTID.
Failover is a whole separate ball of wax. You will need some kind of a reverse proxy (such as MaxScale or HAproxy) or floating IP address in front of your master that can adjust to master changes. (There might be a way to do this client-side, but I wouldn't recommend it.) Something has to monitor the health of the cluster, and when it comes time to promote a slave to the new master, there is a whole sequence of steps that have to be performed. MySQL provides a utility called mysqlfailover to facilitate this process, but as far as I know, it is not compatible with MariaDB. Instead, you might take a look at replication-manager, which seems to be MariaDB's Go-based answer to mysqlfailover. It appears to be a very sophisticated tool.
Master-Slave helps with failover, but does not provide it.
MariaDB Cluster (Galera) does provide failover for most cases, assuming you have 3 nodes.