pt-online-schema-change usage between master and slave mysql server

[ashoknix]

Hi,

I have Master and slave setup with version: 5.5.56-MariaDB MariaDB Server

I need to add index for “create_time” column. I am planning to alter using pt-osc running such command in Master server

pt-online-schema-change D=obs_db,t=ob_status,h=localhost --alter “ADD INDEX (create_time)” --alter-foreign-keys-method=“auto” --execute --set-vars=“innodb_lock_wait_timeout=50”

Do I need to add anymore options for slave?
Will slave get replicated instantly?

Please advise…

Thanks
Ashok

[mirfan]

There are some safeguards in pt-online-schema-change tool to avoid incurring huge slave lags. You can use either of these options:
–max-lag
type: time; default: 1s

Pause the data copy until all replicas lag is less than this value. After each data-copy query (each chunk), the tool looks at the replication lag of all replicas to which it connects, using Seconds_Behind_Master.

https://www.percona.com/doc/percona-toolkit/LATEST/pt-online-schema-change.html#cmdoption-pt-online-schema-change–max-lag

-check-slave-lag
type: string

Pause the data copy until this replica’s lag is less than --max-lag.

https://www.percona.com/doc/percona-toolkit/LATEST/pt-online-schema-change.html#cmdoption-pt-online-schema-change–check-slave-lag

The data copy process is performed in small chunks of data and these queries are replicated to slave(s) instantly.