What is the difference between MySQL Replication and MySQL Cluster?
Group Replication is know as an up to date HA(High Availablity) solution which is supported in official version of MySQL 5.7 since Dec. 2016.It's similar with the other two tools —— MHA(By Yoshinorim) & PXC(By Percona),but not as same as them. Group Replication(I'll call it MGR later) provides features below:
Changes in MySQL 5.7.17 (2016-12-12, General Availability)
MySQL Enterprise Notes
Test Suite Notes
Functionality Added or Changed
- For GCC versions higher than 4.4,
-fno-expensive-optimizationswas replaced with
-ffp-contract=off, which has the effect of enabling more optimizations. Thanks to Alexey Kopytov for the patch. (Bug #24571672, Bug #82760)
MySQL Enterprise Notes
- Enterprise Encryption for MySQL Enterprise Edition now enables server administrators to impose limits on maximum key length by setting environment variables. These can be used to prevent clients from using excessive CPU resources by passing very long key lengths to key-generation operations. For more information, see Enterprise Encryption Usage and Examples. (Bug #19687742)
- RPM packages now are built
-DWITH_NUMA=ONfor platforms with NUMA support: OEL higher than EL5, Fedora, SLES, Docker. (Bug #24689078)
Incompatible Change: These changes were made to mysqld_safe:
Unsafe use of rm and chown澳门新浦京娱乐场网站共同复制，7组复制技能。 in mysqld_safe could result in privilege escalation. chown now can be used only when the target directory is
/var/log. An incompatible change is that if the directory for the Unix socket file is missing, it is no longer created; instead, an error occurs. Due to these changes, /bin/bash is required to runmysqld_safe on Solaris. /bin/sh is still used on other Unix/Linux platforms.
--lediroption now is accepted only on the command line, not in option files.
mysqld_safe ignores the current working directory.
Other related changes:
Initialization scripts that invoke mysqld_safe pass
Initialization scripts create the error log file only if the base directory is
Unused systemd files for SLES were removed.
(Bug #24483092, Bug #25088048)
References: See also: Bug #24464380, Bug #24388753.
MySQL Server now includes a plugin library that enables administrators to introduce an increasing delay in server response to clients after a certain number of consecutive failed connection attempts. This capability provides a deterrent that slows down brute force attacks that attempt to access MySQL user accounts. For more information, see The Connection-Control Plugin.
OpenSSL is ending support for version 1.0.1 in December 2016; see . Consequently, MySQL Commercial Server builds now use version 1.0.2 rather than version 1.0.1, and the linked OpenSSL library for the MySQL Commercial Server has been updated from version 1.0.1 to version 1.0.2j. For a description of issues fixed in this version, see .
This change does not affect the Oracle-produced MySQL Community build of MySQL Server, which uses the yaSSL library instead.
Test Suite Notes
- mysql-test-run.pl could not be run with
--valgrind-option=--tool=custom_tool, for values
custom_toolsuch as massif or helgrind, because it added the options for memcheck that might not be understood by other tools. Also, the mysql-test-run.pl
--callgrindoption did not work because it supplied an invalid
--baseoption tocallgrind. Thanks to Daniel Black for the patch on which the fixes were based. (Bug #23713613, Bug #82039)
Functionality Added or Changed
Incompatible Change; Partitioning: The generic partitioning handler in the MySQL server is deprecated, and will be removed in MySQL 8.0. As part of this change, the mysqld
--skip-partitionoptions as well as the
-DWITH_PARTITION_STORAGE_ENGINEbuild option are also deprecated, and will later be removed; partitioning will no longer be shown in the
INFORMATION_SCHEMA.PLUGINStable or in the output of
Following the removal of the generic partitioning handler, the storage engine used for a given table will be expected to provide its own (“native”) partitioning handler as the
NDBstorage engines currently do. Currently, no other MySQL storage engines provide native partitioning support, nor is any planned for any other storage engines in current or development versions of MySQL.
Use of tables with nonnative partitioning now results in an
ER_WARN_DEPRECATED_SYNTAXwarning. Also, the server performs a check at startup to identify tables that use nonnative partitioning; for any found, the server writes a message to its error log. To disable this check, use the
To prepare for migration to MySQL 8.0, any table with nonnative partitioning should be changed to use an engine that provides native partitioning, or be made nonpartitioned. For example, to change a table to
InnoDB, execute this statement:
ALTER TABLE table_name ENGINE = INNODB;
InnoDB: By default,
InnoDBreads uncommitted data when calculating statistics. In the case of an uncommitted transaction that deletes rows from a table,
InnoDBexcludes records that are delete-marked when calculating row estimates and index statistics, which can lead to non-optimal execution plans for other transactions that are operating on the table concurrently using a transaction isolation level other than
READ UNCOMMITTED. To avoid this scenario, a new configuration option,
innodb_stats_include_delete_marked, can be enabled to ensure that
InnoDBincludes delete-marked records when calculating persistent optimizer statistics. (Bug #23333990)
The systemd service file for mysqld now includes a
Documentationvalue in the
[Unit]section to provide a link to the systemd documentation in the MySQL Reference Manual. (Bug #24735762)
Unit testing now uses Google Mock 1.8. (Bug #24572381, Bug #82823)
If mysqld is invoked with
stderrare redirected to
/dev/nullif connected to a terminal type device, so that mysqld can behave as a true daemon. (Bug #21627629)
libmysqldembedded server library is deprecated and will be removed in a future version of MySQL.
MySQL Group Replication is a new MySQL plugin that enables you to create a highly available distributed MySQL service across a group of MySQL server instances, with data consistency, conflict detection and resolution, and group membership services all built-in. By using a powerful new group communication service, which provides an implementation of the popular Paxos algorithm, the group of MySQL Server instances automatically coordinates on data replication, consistency, and membership. This provides all of the built-in mechanisms necessary for making your MySQL databases highly available.
By default Group Replication operates in single-primary mode where a single server instance, called the primary, accepts write requests. The remaining server instances in the group, called secondaries, function as replicas of the primary. In the event of an unexpected failure of the primary, an automatic primary election process takes place and one of the secondaries is elected as the new primary. Group Replication also supports virtually synchronous multi-primary replication, with certain considerations and restrictions, which offers update everywhere functionality. In this mode all members are equal and you can distribute your reads and writes across all MySQL Server instances in the group.
Regardless of the operating mode, Group Replication provides a dynamic membership service that relies on distributed failure detection. Server instances can join and leave the group dynamically, and you can query the group's membership list at any point through Performance Schema tables. Server instances that join the group automatically synchronize their state with the group by doing an automatic point-in-time recovery which ensures that they reach synchrony with the group.
MySQL Group Replication's virtually synchronous replication is also a fully integrated part of MySQL, using the InnoDB storage engine, the Performance Schema tables, standard GTIDs and the well known replication infrastructure (binary and relay logs, multi-source replication, multi-threaded slave execution, etc.), which makes it a familiar and intuitive experience for existing MySQL users and makes it very easy to integrate with MySQL's standard asynchronous and semisynchronous replication, allowing you to mix and match as needed to create varied and complex replication topologies.
Incompatible Change: A change made in MySQL 5.7.8 for handling of multibyte character sets by
LOAD DATAwas reverted due to the replication incompatibility (Bug #24487120, Bug #82641)
References: See also: Bug #23080148.
NDB Cluster: MySQL Cluster encountered race conditions compiling
lex_hash.h. (Bug #24931655, Bug #83477)
NULLfor a foreign key constraint name (
UNIQUE_CONSTRAINT_NAME) after restarting the server. (Bug #25126722)
InnoDB: A prepared XA transaction was rolled back by a high priority transaction. The high priority transaction should wait if the blocking transaction is in a prepared state. (Bug #25032066)
InnoDBpassed an invalid argument to
syscall(SYS_futex). (Bug #24923840, Bug #83375)
InnoDB: On a MySQL 64-bit build on Windows, a file I/O retry result was misinterpreted due to a missing cast necessary for the correct operation of the retry path, resulting in a failing assertion and operating system error. (Bug #24711351)
InnoDB: The GCC
mach_parse_compressedfunction should load one to five bytes depending on the value of the first byte. Due to a GCC bug, GCC 5 and 6 emit code to load four bytes before the first byte value is checked (GCC Bug #77673). A workaround prevents this behavior.
Thanks to Laurynas Biveinis for the patch. (Bug #24707869, Bug #83073)
InnoDB: Due to a
glibcbug, short-lived detached threads could exit before the caller had returned from
pthread_create(), causing a server exit.
Thanks to Laurynas Biveinis for the patch. (Bug #24605956, Bug #82886)
InnoDB: After increasing the value of
innodb_undo_logsand restarting the server, the number of active undo tablespaces was not increased when assigning undo tablespaces to newly allocated rollback segments. (Bug #24488141)
InnoDBincorrectly reported an error about missing encryption when restoring pages from the doublewrite buffer during recovery. (Bug #24471076)
InnoDB: A cached undo segment was not removed from the rollback segment history during a slow shutdown. (Bug #24450908)
InnoDB: An error during a table-rebuilding operation on a table with only a generated clustered index (
GEN_CLUST_INDEX) raised and assertion due to an error called with an invalid key name. (Bug #24444831)
InnoDB: Rotating the tablespace encryption master key while the server is in read-only mode raised an assertion instead of displaying an error message. (Bug #24404091)
InnoDB: On a table without an explicitly defined primary key,
InnoDBdid not replace the implicit clustered index (
GEN_CLUST_INDEX) when a unique key was defined on a
NOT NULLcolumn. (Bug #24397406)
InnoDB: A high priority transaction involving a foreign key constraint check was not able to kill a lower priority blocking transaction. (Bug #24347476)
InnoDB: Page cleaner threads asserted due to a regression related to the adaptive hash index feature. (Bug #24346574)
References: This issue is a regression of: Bug #21407023.
InnoDBfailed to free memory used by the full-text optimizer thread. (Bug #24331265)
InnoDB: When adding a new index, the server dropped an internally defined foreign key index and attempted to use a secondary index defined on a generated virtual column as the foreign key index, causing a server exit.
InnoDBnow permits a foreign key constraint to reference a secondary index defined on a generated virtual column. (Bug #23533396)
INFORMATION_SCHEMA.FILESquery resulted in a server exit due to a race condition with a concurrent tablespace creation operation. (Bug #23477214)
InnoDB: A table-copying online
ALTER TABLEoperation on a
ROW_FORMAT=REDUNDANTtable with indexed virtual columns raised an assertion. (Bug #22018745)
SHOW ENGINE INNODB STATUSoutput showed a “cleaning up” state for an idle thread. Thread state information was not reset after statement execution. (Bug #21974225, Bug #78777)
InnoDB: After a server restart, concurrent
INSERToperations a table with an auto-increment primary key resulted in a duplicate entry error. The current auto-increment value was not changed after
auto_increment_offsetsettings were modified. (Bug #20989615, Bug #76872)
Replication: When using XA transactions, if a lock wait timeout or deadlock occurred for the applier (SQL) thread on a replication slave, the automatic retry did not work. The cause was that while the SQL thread would do a rollback, it would not roll the XA transaction back. This meant that when the transaction was retried, the first event was
XA STARTwhich was invalid as the XA transaction was already in progress, leading to an
XAER_RMFAILerror. (Bug #24764800)
References: See also: Bug #24923091, Bug #24966941.
Replication: The group commit update of GTIDs has been refactored to improve performance on workloads with many small transactions. (Bug #24398760)
Replication: If the
relay_logoption was not specified in a configuration file, the
relay_log_basenamevariable was being internally constructed on the fly using
relay_log_basenamevariable was not set. When a slave tried to access this uninitialized variable it resulted in an unexpected halt of the server. (Bug #24352667)
Replication: For servers built with yaSSL, using group replication with secure connections could result in timeout failures waiting for view delivery. (Bug #23592214)
Replication: Tables with special
DEFAULTcolumns, such as
DEFAULT CURRENT_TIMESTAMP, that existed only on a slave were not being updated when using row-based replication (
binlog_format=ROW). (Bug #22916743)
XA PREPAREstatement that failed during the intermediate steps could lead to an inconsistent
XAtransaction state, where
ID= -1 but the
binloggedflag was set to
true. This caused asserts while executing
XA ROLLBACKqueries. (Bug #22915670)
Replication: Enabling semisynchronous replication when a server was during the commit stage could cause the master to stop unexpectedly. This was related to the patch for Bug# 75570. (Bug #22202516)
Replication: The number of generated unwanted fseeks into the binary log file being replicated to a slave has been reduced. (Bug #83226, Bug #24763579)
rpl.rpl_binlog_errorstest was failing sporadically on Windows. (Bug #82302, Bug #24330138)
binlog_group_commit_sync_delaywas set to a value between 1 and 9, if
binlog_group_commit_sync_no_delay_countwas set to a value greater than 1, and the number of transaction commits was less than
binlog_group_commit_sync_no_delay_count, these commits hung forever if no more commits were received; and if
binlog_group_commit_sync_no_delay_countwas set to 0, all transaction commits hung forever. (Bug #80652, Bug #22891628)
Replication: Using semisynchronous replication was not possible with more than 1024 simultaneous connections. (Bug #79865, Bug #23581389)
Some Linux startup scripts did not process the
datadirsetting correctly. (Bug #25159791)
CREATE TABLEwith a
DATA DIRECTORYclause could be used to gain extra privileges. (Bug #25092566)
CMakenow avoids configuring the
-fexpensive-optimizationsoption for GCC versions for which the option triggers faulty shift-or optimizations. (Bug #24947597, Bug #83517)
OEL RPM packages now better detect which platforms have multilib support (for which 32-bit and 64-bit libraries can be installed). Thanks to Alexey Kopytov for the patch. (Bug #24925181, Bug #83457)
OEL RPM packages now better detect which platforms do not have multilib support (for which 32-bit and 64-bit libraries can be installed). Thanks to Alexey Kopytov for the patch. (Bug #24916428, Bug #83428)
Information about building MySQL 5.6 compatibility libraries in the MySQL 5.7 and higher
.specfile is needed only for building
libmysqld. Information about building the
InnoDBmemcached plugin was removed. (Bug #24908345, Bug #83409)
Compiling MySQL using Microsoft Visual Studio 2015 Version 14.0.25420.1 in
relwithdebinfomode failed with linking errors. (Bug #24748505)
To better provide atomic file creation, Debian packaging scripts now use the coreutils install command rather than touch, chmod, and chown. (Bug #24688682)
For SLES packages, a typo in the installation script postamble prevented some cleanup from occurring. (Bug #24605300, Bug #82389)
Warnings occurring during
CREATE TABLE ... SELECTcould cause a server exit. (Bug #24595992)
LOAD DATAstatements, input data with too many column values produced only a warning, rather than an error as in MySQL 5.6. An error now occurs. (Bug #24577194, Bug #82830)
For segmentation faults on FreeBSD, the server did not generate a stack trace. (Bug #24566529, Bug #23575445, Bug #81827)
.mylogin.cnfoption file is intended for use by client programs, but the server was reading it as well. The server no longer reads it. (Bug #24557925)
The X Plugin was built with compilation options different from other plugins. (Bug #24555770, Bug #82777)
If mysqladmin shutdown encountered an error determining the server process ID file, it displayed an error message that did not clearly indicate the error was nonfatal. It now indicates that execution continues. (Bug #24496214)
The data structure used for
ZEROFILLcolumns could experience memory corruption, leading eventually to a server exit. (Bug #24489302)
Operation of the mysql-multi.server.sh script was based on
my.cnfin the data directory. That option file is no longer used, so mysql-multi.server.sh has been removed. (Bug #24487870)
Use of very long subpartition names could result in a server exit. Now partition or subpartition names larger than 64 characters produce an
ER_TOO_LONG_IDENTerror. (Bug #24400628, Bug #82429)
Gis_wkb_vector<Gis_point>copy constructor was not explicitly instantiated, causing build problems for the Intel compiler. (Bug #24397833, Bug #82358)
Upgrading from MySQL 5.6 to 5.7.13 and then to 5.7.14 resulted in an incorrect column order in the
mysql.slave_master_infosystem table. (Bug #24384561, Bug #82384)
The AppArmor profile installed by Ubuntu packages was missing an entry permitting
libnumato read a
/syshierarchy path, resulting in server startup failure. (Bug #23854929)
INSERTstatement for which the
VALUESlist produced values for the second or later row using a subquery containing a join, the server could exit after failing to resolve the required privileges. (Bug #23762382)
Infinite recursion could occur if the
audit_logplugin signalled an error while handling an error. (Bug #23717558, Bug #82052)
MySQL now uses
readdir_r(). The latter has been deprecated since
glibc2.24 and caused debug builds of MySQL and builds using GCC 6.1 to fail.
Additionally, several problems resulting in GCC 6.1 compiler warnings were corrected. (Bug #23708395, Bug #24437737, Bug #82515, Bug #24459890, Bug #25103242)
For audit log events in the connection class, the
connection_typevalue was available only for connect events. The value is now available in connect, disconnect, and change-user events. (Bug #23541550)
gettimeofday()could return an invalid value and cause a server shutdown. (Bug #23499695)
keyring_fileplugin could attempt to write keys to its storage file when the file did not exist. To ensure that keys are flushed only when the correct storage file exists,
keyring_filenow stores a SHA-256 checksum of the keyring in the file. Before updating the file, the plugin verifies that it contains the expected checksum. (Bug #23498254)
START GROUP REPLICATIONuses stacked
Srv_sessionand did not return to the correct thread.
START GROUP REPLICATIONand
STOP GROUP REPLICATIONare now removed from the list of permitted commands. (Bug #23337984)
A union query resulting in tuples larger than
max_join_sizecould result in a server exit. (Bug #23303485)
The optimizer could choose
refaccess on a secondary index rather than
rangeaccess on the primary key, even when the cost was higher. (Bug #23259872, Bug #81341)
For a query with
LIMIT, an optimizer trace did not record the optimizer's switch to a different index. (Bug #23227428, Bug #81250)
For some deeply nested expressions, the optimizer failed to detect stack overflow, resulting in a server exit. (Bug #23135667)
ps_truncate_all_tables()function did not work with
read_onlyenabled or for users with the
super_read_onlyenabled, due to errors attempting to truncate Performance Schema tables. The server now skips the
super_read_onlycheck for Performance Schema tables, with the result that
ps_truncate_all_tables()will work under such configurations. (Bug #23103937, Bug #81009)
For sessions created through the X Plugin, incorrect thread attachment/detachment could cause a server exit. (Bug #23057045)
JSONvalue consisted of a large sub-document wrapped in many levels of JSON arrays, objects, or both, serialization of the
JSONvalue sometimes required an excessive amount time to complete. (Bug #23031146)
A binary (in-place) upgrade from MySQL 5.6 to 5.7 followed by a data export performed using mysqlpump resulted in an
Invalid default value for date_columnerror for attempts to reload the dump file. (Bug #22919028, Bug #80706)
SQL statements executed through the X Plugin were not instrumented in the Performance Schema. (Bug #22859462)
DROP INDEXoperations could fail due to inconsistent handling of index prefix lengths for
TEXT-type columns (
TINYTEXTand so forth). (Bug #22740093, Bug #80392)
innodb_numa_interleavesystem variable was erroneously available on some systems that were not NUMA-enabled. Thanks to Tomislav Plavcic for the patch.
CMake now sets the default
WITH_NUMAvalue based on whether the current platform has
NUMAsupport. For platforms without NUMA support, 澳门新浦京娱乐场网站，CMake behaves as follows:
With no NUMA option (the normal case), CMake continues normally, producing only this warning: NUMA library missing or required version not available
-DWITH_NUMA=ON, CMake aborts with this error: NUMA library missing or required version not available
(Bug #22678436, Bug #80288)
When taking the server offline, a race condition within the Performance Schema could lead to a server exit. (Bug #22551677)
On macOS, if a table with an associated trigger was renamed to a new name containing both lowercase and uppercase characters,
DROP TRIGGERfor the trigger resulted in an
ER_NO_SUCH_TABLEerror for the table. (Bug #22512899, Bug #79873)
MYSQL_FIELDC API structure, the
org_tablevalue for derived tables was
*, which could cause failure for queries that depend on this value. The
org_tablevalue for views and derived tables now is set as follows: If the column is selected from a view,
org_tablenames the view. If the column is selected from a derived table,
org_tablenames the base table. If a derived table wraps a view,
org_tablestill names the base table. If the column is an expression,
org_tableis the empty string. (Bug #22364401, Bug #79641)
The Performance Schema
events_statements_summary_by_digesttable could contain multiple rows for the same statement digest and schema combination, rather than the expected single (unique) row. (Bug #22320066, Bug #79533)
For Performance Schema system and status variable tables, variable values expressed in a character set different from
utf8could be truncated or incorrect. (Bug #22313205)
Queries that were grouped on a column of a
BLOB-based type, and that were ordered on the result of the
STDDEV_POP()aggregate function, returned results in the wrong order if
InnoDBtemporary tables were used. (Bug #22275357, Bug #79366)
On Ubuntu, error messages were displayed during upgrades from Community to Commercial packages that made it appear as though mysqld and my_print_defaults had not been installed. Those messages were spurious and have been silenced. (Bug #21807248)
An invalid string value in the
WHEREclause of an
UPDATEstatement, caused an index scan rather than a range scan to be used. For values not present in the index, this could be much slower. Now the optimizer determines this to be an “impossible
WHERE” condition. (Bug #21032418, Bug #76933)
The return value from an
fread()call was not checked. (Bug #20671150)
ALTER TABLEoperation failed to report an error when adding a
DATETIMEcolumn under these conditions: a) the column was
NOT NULLand no default value was supplied; b) strict and
NO_ZERO_DATESQL modes were enabled; c) the table was not empty.
ALTER TABLEoperation failed with an error rather than a warning when adding a
DATETIMEcolumn under these conditions: a) the column was
NOT NULLand no default value was supplied; b) strict SQL mode was enabled and
NO_ZERO_DATESQL mode was not enabled; c) the table was not empty. (Bug #16888677)
听大人讲历史经验，percona server 应该会在1个月后左右公布。
MySQL currently supports two different solutions for creating a high
availability environment and achieving multi-server scalability.
试问你搭建MySQL复制的时候，还在试行备份复苏，在从库举行change master to的操作嘛？假使是那你可就着实落后了。
- *high consistency
As we all know,there're three kinds of replication in MySQL nowadays.Such as,asynchronous replication,(full)synchronous replication,semi-synchronous replication.What's the difference between them?First of all,let's see the intact architecture picture of MySQL replication:
The first form is replication, which MySQL has supported since MySQL version 3.23. Replication in MySQL is currently implemented as an asyncronous master-slave setup that uses a logical log-shipping backend.
本章介绍MySQL官方推荐的一款高可用集群方案MySQL Group Replication。简称：名爵奥迪Q5(组复制)。它是官方推出的一种基于Paxos协议的动静机复制，透彻化解了遵照守旧的异步复制和半一同复制中多少一致性难点不恐怕确定保证的图景。也让MySQL数据库涉及的小圈子更广，深透具有了开辟互连网金融行业的大门。2015年七月MySQL Group Replication推出了第贰个GA版本公布在MySQL5.7.17中。但如今一直投入到生育情形中应用，危害依旧比非常大。提出等其进一步成熟今后，大家再真正投入使用。
A master-slave setup means that one server is designated to act as the master. It is then required to receive all of the write queries. The master then executes and logs the queries, which is then shipped to the slave to execute and hence to keep the same data across all of the replication members.
随着MySQL8.0本子就要与我们汇合，再同盟官方渐渐成熟的高可用集群 Group Replication方案，到那时候再看看什么人照旧大家MySQL的挑战者，全都不在了！MySQL数据库正是小编的迷信，爱您无怨无悔。
MGR protocol lies on the algorithm of Paxos(Which is a kind of consensus protocol usually be used in distributed system and presented by Mr.Lamport.) to guarantee data consistency.What's Paxos?There's something about it below:
Replication is asyncronous, which means that the slave server is not guaranteed to have the data when the master performs the change. Normally, replication will be as real-time as possible. However, there is no guarantee about the time required for the change to propagate to the slave.
theory of Paxos: http://www.the-paper-trail.org/post/2009-02-03-consensus-protocols-paxos/
Replication can be used for many reasons. Some of the more common reasons include scalibility, server failover, and for backup solutions.
Mr Lamport's introduction on wiki:
What will client do?
Scalibility can be achieved due to the fact that you can now do can do SELECT queries across any of the slaves. Write statements however are not improved generally due to the fact that writes have to occur on each of the replication member.
MGR provides a built-in membership
commits transactions to master
receives results from master
Failover can be implemented fairly easily using an external monitoring utility that uses a heartbeat or similar mechanism to detect the failure of a master server. MySQL does not currently do automatic failover as the logic is generally very application dependent. Keep in mind that due to the fact that replication is asynchronous that it is possible that not all of the changes done on the master will have propagated to the slave.
service which can strongly coordinate the servers in the same group to do switchover between master and slave automatically with high efficiency and strong consistency.All members in the same group will communicate with each other from time to time by GSC protocols.The group members always come up to an agreement in an order of global transaction sequence in order to decide whether to commit or abort transactions when commit operations happen.
What will master do?
MySQL replication works very well even across slower connections, and
with connections that aren't continuous. It also is able to be used
across different hardware and software platforms. It is possible to use
replication with most storage engines including MyISAM and InnoDB.
组复制能够在三种情势下运营。 在单主方式下，组复制具备自动选主功效，每一遍只有一个server成员接受创新，别的成员只提供读服务。在多主格局下运作时，全部的 server 成员都足以而且接受创新，没有基本之分，成员剧中人物是一丝一毫对等的。 组复制暗中同意情况下是单主形式，我们能够透过安装参数group_replication_single_primary_mode=off，让其变为多主格局。本章的实战部分正是以多主格局实行MGHighlander复制的搭建。
- executes transactions
- generates binary logs
- dump thread sends contents(binary logs) to slave
- returns results to client
MySQL Cluster is a shared nothing, distributed, partitioning system that uses synchronous replication in order to maintain high availability and performance.
- *high flexibility
What will slave do?
MySQL Cluster is implemented through a separate storage engine called NDB Cluster. This storage engine will automatically partition data across a number of data nodes. The automatic partitioning of data allows for parallelization of queries that are executed. Both reads and writes can be scaled in this fashion since the writes can be distributed across many nodes.
- connects to master
- IO Thread asks for data(binary logs) and gets them
- generates relay logs
- SQL Thread applies data(relay logs)
Internally, MySQL Cluster also uses synchronous replication in order to remove any single point of failure from the system. Since two or more nodes are always guaranteed to have the data fragment, at least one node can fail without any impact on running transactions. Failure detection is automatically handled with the dead node being removed transparent to the application. Upon node restart, it will automatically be re-integrated into the cluster and begin handling requests as soon as possible.
MGR supports both single-primary and multi-primary mode.In the single-primary mode,there's a machenism called "primary election" automatically while failure is detected and only the primary server can update data simultanuously.In the multi-primary mode,update can be done on all the servers in the group even though they update data concurrently.You can choose the appropriate way to implement your MySQL Servers.
Method of different MySQL Replication
There are a number of limitations that currently exist and have to be kept in mind while deciding if MySQL Cluster is the correct solution for your situation.
Currently all of the data and indexes stored in MySQL Cluster are stored in main memory across the cluster. This does restrict the size of the database based on the systems used in the cluster. Work is underway to allow data to be stored on disk and will most likely appear in MySQL version 5.1.
- ***high fault-tolerance
Generally speaking,the data changed on master will be continuously sent to slave.So the data on slave seems to be equal with the master.This mechanism is usually used to backup on slave(reduce the pressure of master),construct HA architecture(failover or separate reading/writing operations),etc.
MySQL Cluster is designed to be used on an internal network as latency is very important for response time. As a result, it is not possible to run a single cluster across a wide geographic distance. In addition, while MySQL Cluster will work over commodity network setups, in order to attain the highest performance possible special clustering interconnects can be used.
Nevertheless,on account of different reasons,slave frequently defers in almost all the scenarios what's often grumbled by MySQL dba.Below are different kinds of MySQL replication.Let's see the details.
Only if most of your servers crash,the service will continuously proceed.There's an "failure detector" machenism when fault occurs or the servers in group don't get privilege to update data.that also prevents "brain-split" when one member cannot communicate with others in the same group(Which usually caused by network failure or something else). it's recommended to implement MGR with three server at least,as the number of tolerance depend on the formula:n=2f 1.For instance,there's five members in the MGR group,so the tolerance is two.*
- asynchronous replication
**Since MySQL 3.2.22,this kind of replication was supported with statement format of binary log.Then,untill MySQL 5.1.5,row format of binary log was supported either.The mechanism of it is that as soon as the master dump thread has sent the binary logs to the slave,the master server returns the result to client.There's nothing to guarantee the binary logs are normally received by the slave(maybe the network failure occurs simultaneously).So it's unsafe in consistency what means your transactions will lose in the replication.This is also the original replication of MySQL.Here's the picture about the procedure:
数据库IP地址 数据库版本音信 主机名 Server-id
One server in group can be replicated from another one automatically until it become equal when adding or removing it.MGR will maintain a view which contains informations about these group members if they changes,All the members join or leave the group voluntarilly or not will dynamically reconfigure the view.*
In order to distinguish MGR and traditional replication technology,let's see the pictures below:
1. Client sends dml operations to the master while the transaction starts.
2. Master executes these dml operations from client in transaction.
3. Generates some binary logs which contains the transaction information.
4. Master will return results to the client immediately after dump thread has sent these binary logs to slave.
5. Slave receives the binary logs by IO_Thread and apply the relay logs by SQL_Thread.
In step 4,master won't judge whether slave has received the binary logs (which are sent by itself) or not.If the master crashs suddenly after it has sent the binary logs,but slave does not receive them at all on account of network delay.Only if the slave takes over the application at this time,the committed transactions will miss which means data loss.This is not commonly acceptable in most important product systems especially in the financial ones.
- synchronous replication
Synchronous replication requires master to return results to client only after the transactions have been committed by all the slaves(receive and apply).This method will severely lead to bad performance on master unless you can guarantee the slaves can commit immediate without any delay(infact it's tough).Now,the only solution of synchronous replication is still the MySQL NDB Cluster.Therefore,it's not recommended to use synchronous replication way.
- semi-synchronous replication
Semi-synchronous replication seems a workaround of above two method which can strongly increase the consistency between master and slave.It's supported since MySQL 5.5 and enhanced in MySQL 5.7.What's the mechanism of semi-sychronouos replication?Master is permitted to return the result to client merely after only one slave has received binary logs,write them to the relay logs and returns an ACK signal to master.There're two ways of it,that is,after_commit & after_sync.Let's see the difference of them:
From the above two pictures,we can see that there's no HA function in the master-slave traditional replication(both asyn mode and semisync mode).whenever the master crashes,the service won't be available anymore.
root@db13:23: [(none)]> show plugins;
after_commit(Since MySQL 5.5):
In most scenarios,master has one or more slaves.Commits of transactions take place merely on the master.Binlogs are transited(asynchronously).Each server has a full copy of data 'cause it shares nothing here.
In this method,master performs a commit before it receives ACK signal from slave.Let's suppose a situation that once master crashs after it commits a transaction but it hasn't receive the ACK signal from slave.Meanwhile,failover makes slave become the new master.How does the slave deal with then?Will the transaction lose?It depends.There're two scenarios:
- Slave has received the binary log,and then turns it into relay log and applys it.There's no transaction loss.
- Slave hasn't received the binary log,the transaction committed by master just now will lose,but the client won't fail(only inconsistent in replication).
Therefore,after_commit cannot guarantee lossless replication.after_commit is the default mode(actually it's the only mode can be use) which is supported by MySQL 5.5 & 5.6.
server_id=1013306gtid_mode=ONenforce_gtid_consistency=ONmaster_info_repository= TABLErelay_log_info_repository= TABLEbinlog_checksum= NONElog_slave_updates=ONlog_bin= binlogbinlog_format= ROWtransaction_write_set_extraction= XXHASH64loose-group_replication_group_name='1f2cee29-f9a2-11e7-8cbb-08002783b39d'loose-group_replication_start_on_boot=offloose-group_replication_local_address='node2:33061'loose-group_replication_group_seeds='node2:33061,node3:33062,proxysql:33063'loose-group_replication_bootstrap_group=offloose-group_replication_single_primary_mode=offloose-group_replication_enforce_update_everywhere_checks=true
Above is the multi-primary mode of MGR,There're something diffrerent such as "certify" and "consensus" in the picture.The consensus based on paxos make sure the consistencies between the masters.but it's still a shared-nothing replication the same as the classical replication.
after_sync(since MySQL 5.7):
MGCRUISER一定要敞开GTID作用gtid_mode = ON，enforce_gtid_consistency = ON
Notice,in multi-primary mode,all ther masters can execute transactions and commit independently,if there's a confilct(which always happens in the certification procedure),for example,they want to update the same row of one table,only one master who has the earlier golobal transaction sequence will get the privilege to finish the operation(what seems like first commit win principle).
名爵ENVISION需求多源复制功效，所以需求将主从库之间的音讯记录到表中。设置master_info_repository = TABLE和relay_log_info_repository = TABLE
In the picture above,the t1 transaction shouldn't be lost because of the master merely commits to the storage engine after receive the ACK signal from slave.In spite of master may crash before receiving ACK signal,no transaction will lose as the master hasn't commit at all.Meanwhile,the t2 transaction also get consistent query here.
- Be compared with MHA & PXC,MGR is the newest supplement in MySQL high availability family.
- There're still few case using MGR to implement in product system nowadays.
- MySQL Servers don't need to failover but the application does.
- The practical usage of MGR is together with some middleware product such as ProxySQL.
In order to improve the data consistency(since after_commit has avoidless deficiency),MySQL official enhances the semi-synchronous replication which can be called "loss-less semi-synchronous replication" in MySQL 5.7 by add after_sync mode in parameter "rpl_semi_sync_master_wait_point".
Caution,semi-synchronous replication may turn into asynchronous replication whenever the delay time of slave surpass the value which is specified in parameter "rpl_semi_sync_master_timeout"(default values is 10000 milliseconds).Why it is permitted?I'm afraid in order to consider the performance of master.Notwithstanding,you can also play a trick to prevent it from being converted over by set a infinite number in this parameter such as "10000000" or above.Especially in case that your product system is too important to not lose data.
Further more,to configure semi-sychronous replication,you should implement the optional plugin component "rpl_semi_sync_master",which can be check by using command "show plugins;"
- Commonly,semi-sync replication is strongly recommended when implements MySQL replication nowadays(with gtid).
- I utterly recommend to upgrade product system to MySQL 5.7 in order to use "after_sync" mode which can avoid data loss.
- Be careful of specify an inappropriate value in parameter "rpl_semi_sync_master_timeout" which will cause converting semi-sync to async replication.
SET GLOBAL group_replication_bootstrap_group = ON;