• This option controls whether user-defined functions that have  only an xxx symbol for the main function  can be loaded.
• If you intend to bind the server to a specific address, be  sure that the mysql.user grant table  contains an account with administrative privileges that you  can use to connect to that address. Otherwise, you will not be  able to shut down the server.
• Global transaction identifiers (GTIDs) are not disabled when  --bootstrap is used.  --bootstrap was used (Bug  #20980271).
• When the server operates in bootstap mode, some functionality  is unavailable that limits the statements permitted in any  file named by the --init-file option.
• Using -DWITH_DEBUG=1 to  configure MySQL with debugging support enables you to use the  --debug="d,parser_debug" option  when you start the server. This causes the Bison parser that  is used to process SQL statements to dump a parser trace to  the server's standard error output.
• This option sets the default authentication plugin. It was  removed in MySQL 5.7.2 and replaced by the  default_authentication_plugin  system variable.
• Read this option file after the global option file but (on  Unix) before the user option file.
• This must be the first option on the command line if it is  used, except that if the server is started with the  --defaults-file and  --install (or  --install-manual) options,  --install (or  --install-manual) must be  first.
• Specify how to use delayed key writes. Delayed key writing  causes key buffers not to be flushed between writes for  MyISAM tables. OFF  disables delayed key writes. ON enables  delayed key writes for those tables that were created with the  DELAY_KEY_WRITE option.  ALL delays key writes for all  MyISAM tables.
• This option tells the server which plugins to load before  loading mandatory built-in plugins and before storage engine  initialization. If multiple  --early-plugin-load options are  given, only the last one is used.
• If the server is started using  --initialize or  --initialize-insecure, plugins  specified by  --early-plugin-load are not  loaded.
• If the server is run with  --help, plugins specified by  --early-plugin-load are loaded  but not initialized. This behavior ensures that plugin options  are displayed in the help message.
• If you use this option on a system on which  lockd does not fully work (such as Linux),  it is easy for mysqld to deadlock
• External locking affects only  MyISAM table access.
• Normally, MySQL does a write of all changes to disk  only after each SQL statement and lets the operating system  handle the synchronizing to disk
• This option tells the server to ignore the given directory  name for purposes of the SHOW  DATABASES statement or  INFORMATION_SCHEMA tables.
• Instances of this option given at server startup are used to  set the ignore_db_dirs system  variable.
• When the server is started with  --initialize, some  functionality is unavailable that limits the statements  permitted in any file named by the  --init-file option.
• In MySQL 5.7.7 and earlier, global transaction identifiers  (GTIDs) were automatically disabled whenever  --initialize was enabled. In  MySQL 5.7.8 and later GTIDs are not disabled when  --initialize is enabled.
• Read SQL statements from this file at startup. Each statement  must be on a single line and should not include comments.
• This option determines the destination for general query log  and slow query log output.
• If you are using this option with the slow query log enabled,  queries that are expected to retrieve all rows are logged
• This option  may be useful for diagnostic purposes, to see the exact text  of statements as received by the server, but for security  reasons is not recommended for production use.
• On Linux and perhaps other systems, you can avoid the need  to run the server as root by changing the  limits.conf file.
• The server logs messages  about statements that are unsafe for statement-based logging  if the value is greater than 0. Aborted connections and  access-denied errors for new connection attempts are logged if  the value is greater than 1.
• This affects only storage engines that use only  table-level locking (MyISAM,  MEMORY, MERGE)
• --memlock works on systems that  support the mlockall() system call; this  includes Solaris, most Linux distributions that use a 2.4 or  higher kernel, and perhaps other Unix systems.
• If recovery is enabled, each time mysqld  opens a MyISAM table, it checks whether the  table is marked as crashed or was not closed properly.
• Do not read any option files. If program startup fails due to  reading unknown options from an option file,  --no-defaults can be used to  prevent them from being read. This must be the first option on  the command line if it is used.
• --skip-plugin-innodb_file_per_table  disables innodb_file_per_table
• Use of the  --plugin prefix for plugin options is  recommended to avoid any question of ambiguity.
• This option tells the server to load the named plugins at  startup. If multiple  --plugin-load options are  given, only the last one is used. Additional plugins to load  may be specified using  --plugin-load-add options.
• After a restart, the plugin is  not loaded unless --plugin-load  is used again. This is in contrast to  INSTALL PLUGIN, which adds an  entry to the mysql.plugins table to cause  the plugin to be loaded for every normal server startup.
• --plugin-load enables plugins  to be loaded even when  --skip-grant-tables is given.  --plugin-load also enables  plugins to be loaded at startup that cannot be loaded at  runtime.
• --plugin-load-add can be given  in the absence of  --plugin-load, but any instance  of --plugin-load-add that  appears before --plugin-load.  has no effect because  --plugin-load resets the set of  plugins to load.
• This option causes the server to block connections by clients  that attempt to use accounts that have passwords stored in the  old (pre-4.1) format.
• Server startup fails with an error if this option is enabled  and the privilege tables are in pre-4.1 format.
• You can cause a running server to start  using the grant tables again by executing mysqladmin  flush-privileges or mysqladmin  reload command from a system shell, or by issuing a  MySQL FLUSH  PRIVILEGES statement after connecting to the server.
• --skip-grant-tables also causes  the disabled_storage_engines  system variable to have no effect.
• you should avoid dropping  partitioned tables with partitioning disabled, or take action  to remove orphaned .par files manually  (if present).
• On Unix, enabling  symbolic links means that you can link a  MyISAM index file or data file to another  directory with the INDEX DIRECTORY or  DATA DIRECTORY options of the  CREATE TABLE statement.
• SYSDATE() by default returns  the time at which it executes, not the time at which the  statement in which it occurs begins executing.
• This option causes most temporary files created by the server  to use a small set of names, rather than a unique name for  each new file.
• The path of the directory to use for creating temporary files.
• If the MySQL  server is acting as a replication slave, you should not set  --tmpdir to point to a  directory on a memory-based file system or to a directory that  is cleared when the server host restarts.

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• A mix of collations may also occur in contexts other than  comparison.
• To resolve questions like these, MySQL checks whether the  collation of one item can be coerced to the collation of the  other.
• f both sides are Unicode, or both sides are not  Unicode, it is an error.
• If one of the sides has a Unicode character set, and  another side has a non-Unicode character set, the side  with Unicode character set wins, and automatic  character set conversion is applied to the non-Unicode  side.
• For an operation with operands from the same character  set but that mix a _bin collation  and a _ci or _cs  collation, the _bin collation is  used.
• The following table illustrates some applications of the  preceding rules.
• For implicit conversion of a numeric or temporal value to a  string
• the result is a character (nonbinary) string  that has a character set and collation determined by the  character_set_connection and  collation_connection system  variables

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• Additional character set and collation system variables are  involved in handling traffic for the connection between a client  and the server. Every client has connection-related character  set and collation system variables.
• For this, the server uses the  character_set_connection  and collation_connection  system variables. It converts statements sent by the client  from character_set_client  to  character_set_connection,  xexcept for string literals that have an introducer (for  example, _utf8mb4 or  _latin2).  collation_connection is  important for comparisons of literal strings. For  comparisons of strings with column values,  collation_connection does  not matter because columns have their own collation, which  has a higher collation precedence.
• The character_set_results  system variable indicates the character set in which the  server returns query results to the client. This includes  result data such as column values, and result metadata such  as column names and error messages.
• SET NAMES indicates what  character set the client will use to send SQL statements to  the server.
• A SET NAMES  'charset_name'  statement is equivalent to these three statements
• collation_connection is  important for comparisons of literal strings. For  comparisons of strings with column values,  collation_connection  does not matter because columns have their own  collation, which has a higher collation precedence
• collation_connection is  important for comparisons of literal strings. For  comparisons of strings with column values,  collation_connection  does not matter because columns have their own  collation, which has a higher collation precedence
• ucs2, utf16,  utf16le, and utf32  cannot be used as a client character set, which means that  they do not work for SET NAMES  or SET CHARACTER SET.
• The OS character set is mapped to the closest MySQL  character set if there is no exact match. If the client does  not support the matching character set, it uses the  compiled-in default.
• When a client connects to the server, it sends the name of the  character set to be used for communication with the server. The  server uses the name to set the  character_set_client,  character_set_results, and  character_set_connection system  variables. In effect, the server performs a  SET NAMES operation using the  character set name.
• If you are using the mysql client with  auto-reconnect enabled (which is not recommended), it is  preferable to use the charset command rather  than SET NAMES.
• If the server does not support the requested character set or  collation, it falls back to using the server character set and  collation to configure the connection.
• If you want the server to perform no conversion of result sets  or error messages, set  character_set_results to  NULL or binary
• The charset command issues a  SET NAMES statement, and also  changes the default character set that mysql  uses when it reconnects after the connection has dropped.
• Attempts to use an inappropriate connection character set or  collation can produce an error, or cause the server to fall back  to its default character set and collation for a given  connection.
• f you specify a character set that the client recognizes but  the server does not, the server falls back to its default  character set and collation.

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• all read-write transactions  commit only after they have been approved by the group.
• Read-only  transactions need no coordination within the group and commit  immediately.
• But all read-write (RW) transactions  commit only after they have been approved by the group.  Read-only (RO) transactions need no coordination within the  group and thus commit immediately. In other words, for any RW  transaction the group needs to decide whether it commits or not,  thus the commit operation is not a unilateral decision from the  originating server. To be precise, when a transaction is ready  to commit at the originating server, the server atomically  broadcasts the write values (rows changed) and the correspondent  write set (unique identifiers of the rows that were updated).  Then a global total order is established for that transaction.  Ultimately, this means that all servers receive the same set of  transactions in the same order. As a consequence, all servers  apply the same set of changes in the same order, therefore they  remain consistent within the group.
• When a read-write transaction is ready to commit at the  originating server, the server atomically broadcasts the write  values (the rows that were changed) and the corresponding write  set (the unique identifiers of the rows that were updated).
• the transaction is sent through an atomic broadcast,  either all servers in the group receive the transaction or none  do. If they receive it, then they all receive it in the same  order with respect to other transactions that were sent before.  All servers therefore receive the same set of transactions in  the same order, and a global total order is established for the  transactions.
• During certification,  conflict detection is carried out at row level
• For applying and externalizing the certified transactions, Group  Replication permits servers to deviate from the agreed order of  the transactions if this does not break consistency and  validity. Group Replication is an eventual consistency system,  meaning that as soon as the incoming traffic slows down or  stops, all group members have the same data content.
• This is in fact a distributed first  commit wins rule.

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