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Glossary

LSN
Each InnoDB page (usually 16kb in size) contains a log sequence number, or LSN. The LSN is the system version number for the entire database. Each page’s LSN shows how recently it was changed.
InnoDB
Storage engine which provides ACID-compliant transactions and foreign key support, among others improvements over MyISAM. It is the default engine for MySQL as of the 5.5 series.
MyISAM
Previous default storage engine for MySQL for versions prior to 5.5. It doesn’t fully support transactions but in some scenarios may be faster than InnoDB. Each table is stored on disk in 3 files: .frm, .MYD, .MYI.
GTID
Global Transaction ID, in Percona XtraDB Cluster it consists of UUID and an ordinal sequence number which denotes the position of the change in the sequence.
HAProxy
HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. It is particularly suited for web sites crawling under very high loads while needing persistence or Layer7 processing. Supporting tens of thousands of connections is clearly realistic with todays hardware. Its mode of operation makes its integration into existing architectures very easy and riskless, while still offering the possibility not to expose fragile web servers to the net.
IST
Incremental State Transfer. Functionality which instead of whole state snapshot can catch up with te group by receiving the missing writesets, but only if the writeset is still in the donor’s writeset cache.
SST
State Snapshot Transfer is the full copy of data from one node to another. It’s used when a new node joins the cluster, it has to transfer data from existing node. There are three methods of SST available in Percona XtraDB Cluster: mysqldump, rsync and xtrabackup. The downside of mysqldump and rsync is that the node becomes READ-ONLY while data is being copied from one node to another (SST applies FLUSH TABLES WITH READ LOCK command). Xtrabackup SST does not require READ LOCK for the entire syncing process, only for syncing the MySQL system tables and writing the information about the binlog, galera and slave information (same as the regular XtraBackup backup). State snapshot transfer method can be configured with the wsrep_sst_method variable.
UUID

Universally Unique IDentifier which uniquely identifies the state and the sequence of changes node undergoes. 128-bit UUID is a classic DCE UUID Version 1 (based on current time and MAC address). Although in theory this UUID could be generated based on the real MAC-address, in the Galera it is always (without exception) based on the generated pseudo-random addresses (“locally administered” bit in the node address (in the UUID structure) is always equal to unity).

Complete structure of the 128-bit UUID field and explanation for its generation are as follows:

From To Length Content
0 31 32 Bits 0-31 of Coordinated Universal Time (UTC) as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582, encoded as big-endian 32-bit number.
32 47 16 Bits 32-47 of UTC as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582, encoded as big-endian 16-bit number.
48 59 12 Bits 48-59 of UTC as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582, encoded as big-endian 16-bit number.
60 63 4 UUID version number: always equal to 1 (DCE UUID).
64 69 6 most-significants bits of random number, which generated from the server process PID and Coordinated Universal Time (UTC) as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582.
70 71 2 UID variant: always equal to binary 10 (DCE variant).
72 79 8 8 least-significant bits of random number, which generated from the server process PID and Coordinated Universal Time (UTC) as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582.
80 80 1 Random bit (“unique node identifier”).
81 81 1 Always equal to the one (“locally administered MAC address”).
82 127 46 Random bits (“unique node identifier”): readed from the /dev/urandom or (if /dev/urandom is unavailable) generated based on the server process PID, current time and bits of the default “zero node identifier” (entropy data).
XtraBackup
Percona XtraBackup is an open-source hot backup utility for MySQL - based servers that doesn’t lock your database during the backup.
XtraDB
Percona XtraDB is an enhanced version of the InnoDB storage engine, designed to better scale on modern hardware, and including a variety of other features useful in high performance environments. It is fully backwards compatible, and so can be used as a drop-in replacement for standard InnoDB. More information here.
XtraDB Cluster
Percona XtraDB Cluster is a high availability solution for MySQL.
Percona XtraDB Cluster
Percona XtraDB Cluster (PXC) is a high availability solution for MySQL.
my.cnf
This file refers to the database server’s main configuration file. Most Linux distributions place it as /etc/mysql/my.cnf or /etc/my.cnf, but the location and name depends on the particular installation. Note that this is not the only way of configuring the server, some systems does not have one even and rely on the command options to start the server and its defaults values.
cluster replication
Normal replication path for cluster members. Can be encrypted (not by default) and unicast or multicast (unicast by default). Runs on tcp port 4567 by default.
datadir
The directory in which the database server stores its databases. Most Linux distribution use /var/lib/mysql by default.
donor node
The node elected to provide a state transfer (SST or IST).
ibdata
Default prefix for tablespace files, e.g. ibdata1 is a 10MB autoextendable file that MySQL creates for the shared tablespace by default.
joiner node
The node joining the cluster, usually a state transfer target.
node
A cluster node – a single mysql instance that is in the cluster.
primary cluster
A cluster with quorum. A non-primary cluster will not allow any operations and will give Unknown command errors on any clients attempting to read or write from the database.
quorum
A majority (> 50%) of nodes. In the event of a network partition, only the cluster partition that retains a quorum (if any) will remain Primary by default.
split brain
Split brain occurs when two parts of a computer cluster are disconnected, each part believing that the other is no longer running. This problem can lead to data inconsistency.
.frm
For each table, the server will create a file with the :file`.frm` extension containing the table definition (for all storage engines).
This documentation is developed in Launchpad as part of the Percona XtraDB Cluster 5.6.
If you spotted inaccuracies, errors, don't understood it or you think something is missing or should be improved, please file a bug.


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