You should now see information about the NDB cluster engine, beginning with connection parameters:. This redundancy allows your MySQL cluster to continue operating even if one of the data nodes fails.
It also means that your SQL queries will be load balanced across the two data nodes. You can try shutting down one of the data nodes to test cluster stability. The simplest test would be to restart the data node Droplet in order to fully test the recovery process.
This is the first test that indicates that the MySQL cluster, server, and client are working. The above shows that there are two data nodes connected with node-id s 2 and 3. There is also one management node with node-id 1 and one MySQL server with node-id 4. The management console is very powerful and gives you many other options for administering the cluster and its data, including creating an online backup.
For more information consult the official MySQL documentation. The concluding step of this guide shows you how to create and insert test data into this MySQL Cluster. Note that in order to use cluster functionality, the engine must be specified explicitly as NDB. If you use InnoDB default or any other engine, you will not make use of the cluster. We have explicitly specified the engine ndbcluster in order to make use of the cluster.
When you insert data into and select data from an ndbcluster table, the cluster load balances queries between all the available data nodes. This improves the stability and performance of your MySQL database installation.
You can also set the default storage engine to ndbcluster in the my. Where would you like to share this to? Learn more. Ask Question. Asked 9 years, 2 months ago. Active 4 years, 10 months ago.
Viewed 6k times. What's the minimum amount of hosts to achieve full HA in case of one node failure? Failed server can be any of MySQL Cluster components management, sql or data I don't need extreme performance, just fully automated server failure handling on small number of servers From the MySQL Cluster documentation I know that I need at least two full copies of data replicas.
Improve this question. Matthias Matthias 1 1 silver badge 2 2 bronze badges. It all depends on what type s of failure modes you're trying to protect against. Also think about maintenance, if you have to take one node down for updates etc. I would put at least 3 nodes in the cluster. I just want to get 'can-sleep-at-night' or 'can-go-for-holidays' level of HA.
Probability of multiple server failure at the same time in such small setup is low and I accept it. It's also acceptable to have temporary SPoF during scheduled downtime of one host — Matthias.
Add a comment. Active Oldest Votes. Improve this answer. I'm aware of HA issues with all other elements of my infrastructure but the database is hardest one. Matthias There is no relevant difference. The minimum value of N for any required component in a system is always 1. Therefore 2 is always the minimum number of servers required for redundancy.
This means that queries against nonindexed columns can run faster than previously by a factor of as much as 5 to 10 times, times the number of data nodes , because multiple CPUs can work on the query in parallel.
This is because the primary key is not stored in the index memory anymore. New optimizations. One optimization that merits particular attention is that a batched read interface is now used in some queries.
For example, consider the following query:. This query will be executed 2 to 3 times more quickly than in previous MySQL Cluster versions due to the fact that all 10 key lookups are sent in a single batch rather than one at a time.
Previously, this number was Currently, there are no plans to address these in coming releases of MySQL 5. This information is intended to be complete with respect to the conditions just set forth.
You can report any discrepancies that you encounter to the MySQL bugs database using the instructions given in Section 1. If we do not plan to fix the problem in MySQL 5. Temporary tables. Temporary tables are not supported. Indexes and keys in NDB tables. Column width. Attempting to create an index on an NDB table column whose width is greater than bytes succeeds, but only the first bytes are actually used for the index.
There are no prefix indexes; only entire columns can be indexed. The size of an NDB column index is always the same as the width of the column in bytes, up to and including bytes, as described earlier in this section. Also see Section BIT columns. A BIT column cannot be a primary key, unique key, or index, nor can it be part of a composite primary key, unique key, or index.
MySQL Cluster and geometry data types. However, spatial indexes are not supported. Memory usage and recovery. Memory consumed when data is inserted into an NDB table is not automatically recovered when deleted, as it is with other storage engines. Instead, the following rules hold true:. However, this memory can be made available for general re-use by performing a rolling restart of the cluster. Limits imposed by the cluster's configuration. A number of hard limits exist which are configurable, but available main memory in the cluster sets limits.
See the complete list of configuration parameters in Section Most configuration parameters can be upgraded online. These hard limits include:. Database memory size and index memory size DataMemory and IndexMemory , respectively. DataMemory is allocated as 32KB pages. As each DataMemory page is used, it is assigned to a specific table; once allocated, this memory cannot be freed except by dropping the table. Different limits related to tables and indexes.
For example, the maximum number of ordered indexes in the cluster is determined by MaxNoOfOrderedIndexes , and the maximum number of ordered inexes per table is Memory usage. All Cluster table rows are of fixed length.
Node and data object maximums. The following limits apply to numbers of cluster nodes and metadata objects:. The maximum number of metadata objects in MySQL 5. This limit is hard-coded. These include the following:. Transaction isolation level. This gives rise to two related issues of which you should be aware whenever executing SELECT statements on tables that contain columns of these types:. This is done to guarantee consistency.
For any SELECT which uses a primary key lookup or unique key lookup to retrieve any columns that use any of the BLOB or TEXT data types and that is executed within a transaction, a shared read lock is held on the table for the duration of the transaction—that is, until the transaction is either committed or aborted.
This does not occur for queries that use index or table scans. Either of the following queries on t causes a shared read lock, because the first query uses a primary key lookup and the second uses a unique key lookup:.
However, none of the four queries shown here causes a shared read lock:. This is because, of these four queries, the first uses an index scan, the second and third use table scans, and the fourth, while using a primary key lookup, does not retrieve the value of any BLOB or TEXT columns.
You can help minimize issues with shared read locks by avoiding queries that use primary key lookups or unique key lookups to retrieve BLOB or TEXT columns, or, in cases where such queries are not avoidable, by committing transactions as soon as possible afterward. There are no partial transactions, and no partial rollbacks of transactions. This behavior differs from that of other transactional storage engines such as InnoDB that may roll back individual statements. Transactions and memory usage.
As noted elsewhere in this chapter, MySQL Cluster does not handle large transactions well; it is better to perform a number of small transactions with a few operations each than to attempt a single large transaction containing a great many operations. Among other considerations, large transactions require very large amounts of memory.
Because of this, the transactional behavior of a number of MySQL statements is effected as described in the following list:. It is not possible to know ahead of time when such commits take place.
In any case, this operation is rolled back when the copy is deleted. Starting, stopping, or restarting a node may give rise to temporary errors causing some transactions to fail. These include the following cases:. Temporary errors. When first starting a node, it is possible that you may see Error Temporary failure, distribution changed and similar temporary errors. Errors due to node failure. The stopping or failure of any data node can result in a number of different node failure errors.
However, there should be no aborted transactions when performing a planned shutdown of the cluster. In either of these cases, any errors that are generated must be handled within the application. This should be done by retrying the transaction. See also Section Database names, table names and attribute names cannot be as long in NDB tables as when using other table handlers.
Attribute names are truncated to 31 characters, and if not unique after truncation give rise to errors. Database names and table names can total a maximum of characters. In other words, the maximum length for an NDB table name is characters, less the number of characters in the name of the database of which that table is a part.
Table names containing special characters. NDB tables whose names contain characters other than letters, numbers, dashes, and underscores and which are created on one SQL node may not be discovered correctly by other SQL nodes.
Bug Number of tables and other database objects. Attributes per table. The maximum number of attributes that is, columns and indexes per table is limited to Row size.
The maximum permitted size of any one row is bytes. A number of features supported by other storage engines are not supported for NDB tables. Trying to use any of these features in MySQL Cluster does not cause errors in or of itself; however, errors may occur in applications that expects the features to be supported or enforced:.
Foreign key constraints. Index prefixes. Savepoints and rollbacks. Durability of commits. There are no durable commits on disk. Commits are replicated, but there is no guarantee that logs are flushed to disk on commit. Range scans. Reliability of Records in range. The Records in range statistic is available but is not completely tested or officially supported. This may result in nonoptimal query plans in some cases.
Unique hash indexes. Machine architecture. The following issues relate to physical architecture of cluster hosts:. All machines used in the cluster must have the same architecture.
That is, all machines hosting nodes must be either big-endian or little-endian, and you cannot use a mixture of both. For example, you cannot have a management node running on a PowerPC which directs a data node that is running on an x86 machine. This restriction does not apply to machines simply running mysql or other clients that may be accessing the cluster's SQL nodes.
Adding and dropping of data nodes. Online adding or dropping of data nodes is not currently possible. In such cases, the entire cluster must be restarted. Backup and restore between architectures. It is also not possible to perform a Cluster backup and restore between different architectures.
For example, you cannot back up a cluster running on a big-endian platform and then restore from that backup to a cluster running on a little-endian system. Online schema changes. Binary logging. MySQL Cluster has the following limitations or restrictions with regard to binary logging:. Only the following schema operations are logged in a cluster binlog which is not on the mysqld executing the statement:.
Multiple SQL nodes. No distributed table locks. This is also true for a lock issued by any statement that locks tables as part of its operations. See next item for an example. However, if the database partitioning scheme is done at the application level and no transactions take place across these partitions, replication can be made to work. Database autodiscovery. However, autodiscovery of tables is supported in such cases. As of MySQL 5. Once this has been done for a given MySQL server, that server should be able to detect the database tables without error.
DDL operations. If a data node fails while trying to perform one of these, the data dictionary is locked and no further DDL statements can be executed without restarting the cluster. Multiple management nodes. When using multiple management servers:. You must give nodes explicit IDs in connectstrings because automatic allocation of node IDs does not work across multiple management servers.
You must take extreme care to have the same configurations for all management servers. No special checks for this are performed by the cluster. Prior to MySQL 5. See Bug and Bug for more information. Multiple data node processes. While it is possible to run multiple cluster processes concurrently on a single host, it is not always advisable to do so for reasons of performance and high availability, as well as other considerations.
In particular, in MySQL 5. We may support multiple data nodes per host in a future MySQL release, following additional testing. However, in MySQL 5. Multiple network addresses. Multiple network addresses per data node are not supported. Use of these is liable to cause problems: In the event of a data node failure, an SQL node waits for confirmation that the data node went down but never receives it because another route to that data node remains open.
This can effectively make the cluster inoperable. It is possible to use multiple network hardware interfaces such as Ethernet cards for a single data node, but these must be bound to the same address. This also means that it not possible to use more than one [tcp] section per connection in the config. Character set support. Character set directory. Beginning with MySQL 5. Previously, ndbd in MySQL 5. Metadata objects. Query cache. Unlike the case in MySQL 4. See Section 7.
It was possible to work around this issue by removing the constraint, then dropping the unique index, performing any inserts, and then adding the unique index again. See Bug Whereas the examples in Section This section covers hardware and software requirements; networking issues; installation of MySQL Cluster; configuration issues; starting, stopping, and restarting the cluster; loading of a sample database; and performing queries. Basic assumptions. This How-To makes the following assumptions:.
The cluster is to be set up with four nodes, each on a separate host, and each with a fixed network address on a typical Ethernet network as shown here:. In the interest of simplicity and reliability , this How-To uses only numeric IP addresses. However, if DNS resolution is available on your network, it is possible to use host names in lieu of IP addresses in configuring Cluster.
Consider two machines with the host names ndb1 and ndb2 , both in the cluster network domain. In both instances, ndb1 routes ndb1. The result is that each data node connects to the management server, but cannot tell when any other data nodes have connected, and so the data nodes appear to hang while starting. You should also be aware that you cannot mix localhost and other host names or IP addresses in config. For these reasons, the solution in such cases other than to use IP addresses for all config.
Each host in our scenario is an Intel-based desktop PC running a supported operating system installed to disk in a standard configuration, and running no unnecessary services. Also for the sake of simplicity, we also assume that the file systems on all hosts are set up identically. In the event that they are not, you should adapt these instructions accordingly.
Standard Mbps or 1 gigabit Ethernet cards are installed on each machine, along with the proper drivers for the cards, and that all four hosts are connected through a standard-issue Ethernet networking appliance such as a switch. All machines should use network cards with the same throughout. That is, all four machines in the cluster should have Mbps cards or all four machines should have 1 Gbps cards.
Note that MySQL Cluster is not intended for use in a network for which throughput is less than Mbps or which experiences a high degree of latency. For this reason among others , attempting to run a MySQL Cluster over a wide area network such as the Internet is not likely to be successful, and is not supported in production. We assume that each machine has sufficient memory for running the operating system, host NDB process, and on the data nodes storing the database.
Although we refer to a Linux operating system in this How-To, the instructions and procedures that we provide here should be easily adaptable to other supported operating systems. We also assume that you already know how to perform a minimal installation and configuration of the operating system with networking capability, or that you are able to obtain assistance in this elsewhere if needed.
This section covers the steps necessary to install the correct binaries for each type of Cluster node. Oracle provides precompiled binaries that support MySQL Cluster, and there is generally no need to compile these yourself. For setting up a cluster using MySQL's binaries, the first step in the installation process for each cluster host is to download the file mysql If you do require a custom binary, see Section 2. RPMs are also available for both bit and bit Linux platforms.
For more information about these additional programs, see Section The glibc version number if present—shown here as glibc23 , and architecture designation shown here as i should be appropriate to the machine on which the RPM is to be installed.
See Section 2. After installing from RPM, you still need to configure the cluster as discussed in Section After completing the installation, do not yet start any of the binaries. We show you how to do so following the configuration of all nodes. On each of the machines designated to host data or SQL nodes, perform the following steps as the system root user:.
Some OS distributions create these as part of the operating system installation process. If they are not already present, create a new mysql user group, and then add a mysql user to this group:.
The syntax for useradd and groupadd may differ slightly on different versions of Unix, or they may have different names such as adduser and addgroup. Change location to the directory containing the downloaded file, unpack the archive, and create a symlink to the mysql directory named mysql.
Change location to the mysql directory and run the supplied script for creating the system databases:. Set the necessary permissions for the MySQL server and data directories:. This piece of information is essential when configuring the management node.
Copy the MySQL startup script to the appropriate directory, make it executable, and set it to start when the operating system is booted up:. Here we use Red Hat's chkconfig for creating links to the startup scripts; use whatever means is appropriate for this purpose on your operating system and distribution, such as update-rc. Remember that the preceding steps must be performed separately on each machine where an SQL node is to reside. It also installs the mysql.
The RPM installer should take care of general configuration issues such as creating the mysql user and group, if needed automatically. SQL node installation: building from source.
Follow the steps given in Section 2. If you want to run multiple SQL nodes, you can use a copy of the same mysqld executable and its associated support files on several machines. If you configure the build with a nondefault --prefix , you need to adjust the directory accordingly. Data node installation: RPM Files. Data node installation: building from source. The only executable required on a data node host is ndbd mysqld , for example, does not have to be present on the host machine.
For installing on multiple data node hosts, only ndbd need be copied to the other host machine or machines. This assumes that all data node hosts use the same architecture and operating system; otherwise you may need to compile separately for each different platform.
Management node installation:. Installation of the management node does not require the mysqld binary. Both of these binaries also be found in the. Change location to the directory into which you copied the files, and then make both of them executable:. Management node installation: RPM file. Copy this RPM to the computer intended to host the management node, and then install it by running the following command as the system root user replace the name shown for the RPM as necessary to match that of the Storage engine management RPM downloaded from the MySQL web site :.
Copy this RPM to the same computer as the management node, and then install it by running the following command as the system root user again, replace the name shown for the RPM as necessary to match that of the Storage engine basic tools RPM downloaded from the MySQL web site :.
Management node installation: building from source. Neither of these executables requires a specific location on the host machine's file system. In Section For our four-node, four-host MySQL Cluster, it is necessary to write four configuration files, one per node host.
Each data node or SQL node requires a my. For more information on connectstrings, see Section The management node needs a config. The my. Create the file if it does not exist. For example:. We show vi being used here to create the file, but any text editor should work just as well.
For each data node and SQL node in our example setup, my. After entering the preceding information, save this file and exit the text editor. Otherwise, these statements will fail with an error. This is by design. Configuring the management node. The first step in configuring the management node is to create the directory in which the configuration file can be found and then to create the file itself. For example running as root :.
For our representative setup, the config. After all the configuration files have been created and these minimal options have been specified, you are ready to proceed with starting the cluster and verifying that all processes are running. We discuss how this is done in Section For more detailed information about the available MySQL Cluster configuration parameters and their uses, see Section The default port for Cluster management nodes is ; the default port for data nodes is Starting the cluster is not very difficult after it has been configured.
Each cluster node process must be started separately, and on the host where it resides. The management node should be started first, followed by the data nodes, and then finally by any SQL nodes:. On the management host, issue the following command from the system shell to start the management node process:. On each of the data node hosts, run this command to start the ndbd process:.
If all has gone well, and the cluster has been set up correctly, the cluster should now be operational. The output should look like that shown here, although you might see some slight differences in the output depending upon the exact version of MySQL that you are using:.
There are two points to keep in mind:. This hidden key takes up space just as does any other table index. It is not uncommon to encounter problems due to insufficient memory for accommodating these automatically created indexes. There are two ways that this can be accomplished. One of these is to modify the table definition before importing it into the Cluster database. This must be done for the definition of each table that is to be part of the clustered database. MySQL Cluster's unique parallel query engine and distributed cross partition queries give an always consistent access to the entire distributed and partitioned dataset making scalable applications programing straightforward and simple.
Cluster has data locality awareness build into its APIs. No name or data management nodes are needed. Point selects go to the correct node, and the closest copy of the dataset. Update-anywhere geographic replication enables multiple clusters to be distributed geographically for disaster recovery and the scalability of global web services.
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