常用GHOST模板
##================================================## mysql_ip="127.0.0.1" mysql_port=3358 ghost_user="root" ghost_password="123.com" ghost_database="test1" ghost_table="tb002" ghost_command="ADD C4 INT COMMENT '测试列'" ./gh-ost --allow-on-master --max-load="Threads_running=256" --critical-load="Threads_running=512" --chunk-size=1000 --initially-drop-old-table --initially-drop-ghost-table --initially-drop-socket-file --timestamp-old-table --force-table-names="" --host="${mysql_ip}" --port="${mysql_port}" --user="${ghost_user}" --password="${ghost_password}" --database="${ghost_database}" --table="${ghost_table}" --alter="${ghost_command}" --verbose --execute
GHOST常用参数：
1、如果希望直接读取主库BINLOG，需要指定allow-on-master参数 2、如果想避免上次操作失败产生的临时表导致新操作失败，建议使用initially-drop-ghost-table和initially-drop-socket-file参数 3、如果希望GHOST操作完成后删除源表，使用ok-to-drop-table参数 4、如果希望GHOST操作完成后保留源表，建议使用timestamp-old-table参数且不使用ok-to-drop-table参数 5、使用参数max-load来控制主库繁忙时暂停GHOST运行 6、使用参数critical-load来控制主库繁忙时终止GHOST运行 7、使用参数throttle-flag-file或throttle-query来控制GHOST暂停运行 8、使用参数panic-flag-file来控制GHOST停止运行 9、使用参数throttle-control-replicas来控制GHOST对从库复制延迟的影响
GHOST建议：
1、避免同一时间允许多个GHOST 2、请勿使用GHOST来创建唯一索引 3、建议从主库读取BINLOG，执行效率较高 4、建议设置critical-load和max-load时仅考虑Threads_running的值，使用Threads_connected容易因连接暴涨导致GHOST暂停或中止 5、在磁盘空间足够的条件下，使用timestamp-old-table来保存源表，一方面立即删除源表会造成IO压力，另一方面防止执行中出现BUG或误操作。
GHOST所有参数：
Usage of gh-ost: -allow-master-master 当运行MM双主模式时需要显示设置。 -allow-nullable-unique-key 设置是否运行唯一键列中使用NULL值，使用ghost创建唯一索引，存在数据丢失风险，慎用！ -allow-on-master 当使用主节点的BINLOG来操作时，需要设置该值为ON。 -alter string 修改命令，不包含ALTER TABLE部分。 -approve-renamed-columns ALTER 当使用ghost进行修改列名操作，需要设置该值 -ask-pass 提升输入密码 -assume-master-host string 在双主或多主复制场景下，设置以哪个主节点的BINLOG为主。 -assume-rbr 假定使用基于ROW格式的复制模式 -check-flag Check if another flag exists/supported. This allows for cross-version scripting. Exits with 0 when all additional provided flags exist, nonzero otherwise. You must provide (dummy) values for flags that require a value. Example: gh-ost --check-flag --cut-over-lock-timeout-seconds --nice-ratio 0 -chunk-size int 设置每个批次复制数据的行数，取值范围100至100000，默认为1000 -concurrent-rowcount (with --exact-rowcount), when true (default): count rows after row-copy begins, concurrently, and adjust row estimate later on; when false: first count rows, then start row copy (default true) 设置对拷贝记录的计数方式。 -conf string 配置文件的路径 -critical-load string Comma delimited status-name=threshold, same format as --max-load. When status exceeds threshold, app panics and quits 设置GHOST运行的最大阈值，当超过该阈值后，终止GHOST运行。 -critical-load-hibernate-seconds int When nonzero, critical-load does not panic and bail out; instead, gh-ost goes into hibernate for the specified duration. It will not read/write anything to from/to any server 当该值不为0时，如果达到critical-load设置的阈值，会休眠指定时间，然后再次检查。 -critical-load-interval-millis int When 0, migration immediately bails out upon meeting critical-load. When non-zero, a second check is done after given interval, and migration only bails out if 2nd check still meets critical load 设置达到critical-load设置的阈值后的检查间隔。 -cut-over string choose cut-over type (default|atomic, two-step) (default "atomic") 设置切换源表和新表表名的操作方式，默认为自动 -cut-over-lock-timeout-seconds int Max number of seconds to hold locks on tables while attempting to cut-over (retry attempted when lock exceeds timeout) (default 3) 设置在cut-over时获取表锁的超时时间。 -database string database name (mandatory) 数据库名 -debug debug mode (very verbose) DEBUG模式 -default-retries int Default number of retries for various operations before panicking (default 60) 默认重试次数 -discard-foreign-keys DANGER! This flag will migrate a table that has foreign keys and will NOT create foreign keys on the ghost table, thus your altered table will have NO foreign keys. This is useful for intentional dropping of foreign keys 设置是否丢弃外键，谨慎设置。 -dml-batch-size int batch size for DML events to apply in a single transaction (range 1-100) (default 10) -exact-rowcount actually count table rows as opposed to estimate them (results in more accurate progress estimation) -execute actually execute the alter & migrate the table. Default is noop: do some tests and exit 设置运行GHOST操作，默认不执行，仅检查并退出。 -force-named-cut-over When true, the 'unpostpone|cut-over' interactive command must name the migrated table -force-table-names string table name prefix to be used on the temporary tables 设置临时表的前缀 -heartbeat-interval-millis int how frequently would gh-ost inject a heartbeat value (default 100) 设置检查心跳时间间隔 -help Display usage -hooks-hint string arbitrary message to be injected to hooks via GH_OST_HOOKS_HINT, for your convenience -hooks-path string directory where hook files are found (default: empty, ie. hooks disabled). Hook files found on this path, and conforming to hook naming conventions will be executed -host string MySQL hostname (preferably a replica, not the master) (default "127.0.0.1") -initially-drop-ghost-table Drop a possibly existing Ghost table (remains from a previous run?) before beginning operation. Default is to panic and abort if such table exists 设置是否删除已存在的ghost表，默认不删除，如果ghost表存在，则立即退出。 -initially-drop-old-table Drop a possibly existing OLD table (remains from a previous run?) before beginning operation. Default is to panic and abort if such table exists 设置是否删除已存在的OLD表，默认不删除，如果存在，则立即退出。 -initially-drop-socket-file Should gh-ost forcibly delete an existing socket file. Be careful: this might drop the socket file of a running migration! 设置是否删除已有的socket文件 -master-password string MySQL password on master, if different from that on replica. Requires --assume-master-host -master-user string MySQL user on master, if different from that on replica. Requires --assume-master-host -max-lag-millis int replication lag at which to throttle operation (default 1500) 设置复制延迟阈值，如果复制延迟超过该阈值，则暂停GHOST操作。 -max-load string Comma delimited status-name=threshold. e.g: 'Threads_running=100,Threads_connected=500'. When status exceeds threshold, app throttles writes 设置GHOST允许阈值，如果超过该值，则暂停GHOST操作。 -migrate-on-replica Have the migration run on a replica, not on the master. This will do the full migration on the replica including cut-over (as opposed to --test-on-replica) -nice-ratio float force being 'nice', imply sleep time per chunk time; range: [0.0..100.0]. Example values: 0 is aggressive. 1: for every 1ms spent copying rows, sleep additional 1ms (effectively doubling runtime); 0.7: for every 10ms spend in a rowcopy chunk, spend 7ms sleeping immediately after 设置显示GHOST进度的格式 -ok-to-drop-table Shall the tool drop the old table at end of operation. DROPping tables can be a long locking operation, which is why I'm not doing it by default. I'm an online tool, yes? 设置GHOST完成后是否删除OLD表，对于超大表，删除表操作会持续很长时间，并且造成性能问题，建议将表删除操作放到业务低峰期操作。 -panic-flag-file string when this file is created, gh-ost will immediately terminate, without cleanup 当GHOST检查到该文件存在时，会立即退出而不做任何清理。 -password string MySQL password -port int MySQL port (preferably a replica, not the master) (default 3306) -postpone-cut-over-flag-file string while this file exists, migration will postpone the final stage of swapping tables, and will keep on syncing the ghost table. Cut-over/swapping would be ready to perform the moment the file is deleted. 当GHOST检查到该文件存在时，会将切换表名操作延期，直到该文件被删除。 -quiet quiet -replica-server-id uint server id used by gh-ost process. Default: 99999 (default 99999) 指定GHOST操作实例的server-id -replication-lag-query string Deprecated. gh-ost uses an internal, subsecond resolution query 已弃用。 -serve-socket-file string Unix socket file to serve on. Default: auto-determined and advertised upon startup 指定实例使用的socket文件路径 -serve-tcp-port int TCP port to serve on. Default: disabled -skip-foreign-key-checks set to 'true' when you know for certain there are no foreign keys on your table, and wish to skip the time it takes for gh-ost to verify that 忽略外键检查 -skip-renamed-columns ALTER in case your ALTER statement renames columns, gh-ost will note that and offer its interpretation of the rename. By default gh-ost does not proceed to execute. This flag tells gh-ost to skip the renamed columns, i.e. to treat what gh-ost thinks are renamed columns as unrelated columns. NOTE: you may lose column data 忽略列名修改操作 -stack add stack trace upon error -switch-to-rbr let this tool automatically switch binary log format to 'ROW' on the replica, if needed. The format will NOT be switched back. I'm too scared to do that, and wish to protect you if you happen to execute another migration while this one is running 使用GHOST工具修改复制格式为ROW模式 -table string table name (mandatory) 修改表的表名 -test-on-replica Have the migration run on a replica, not on the master. At the end of migration replication is stopped, and tables are swapped and immediately swap-revert. Replication remains stopped and you can compare the two tables for building trust 在复制节点上进行测试 -test-on-replica-skip-replica-stop When --test-on-replica is enabled, do not issue commands stop replication (requires --test-on-replica) -throttle-additional-flag-file string operation pauses when this file exists; hint: keep default, use for throttling multiple gh-ost operations (default "/tmp/gh-ost.throttle") 当该文件存在时，GHOST操作会暂停，默认值为/tmp/gh-ost.throttle -throttle-control-replicas string List of replicas on which to check for lag; comma delimited. Example: myhost1.com:3306,myhost2.com,myhost3.com:3307 设置要复制延迟的从库 -throttle-flag-file string operation pauses when this file exists; hint: use a file that is specific to the table being altered 当该文件存在时，GHOST操作会暂停 -throttle-http string when given, gh-ost checks given URL via HEAD request; any response code other than 200 (OK) causes throttling; make sure it has low latency response 基于HTTP方式来决定GHOST暂停 -throttle-query string when given, issued (every second) to check if operation should throttle. Expecting to return zero for no-throttle, >0 for throttle. Query is issued on the migrated server. Make sure this query is lightweight 基于QUERY方式来决定GHOST暂停 -timestamp-old-table Use a timestamp in old table name. This makes old table names unique and non conflicting cross migrations GHOST操作完成后，将老表设置带有时间戳 -tungsten explicitly let gh-ost know that you are running on a tungsten-replication based topology (you are likely to also provide --assume-master-host) tungsten-replication是一种异构复制技术，如MySQL到MongoDB的复制 -user string MySQL user -verbose verbose 设置该参数会导致GHOST输出更多详细信息 -version Print version & exit