Schema change is one of the crucial tasks in MySQL with huge tables. Schema change can cause locks.
What is gh-ost?
gh-ost is a triggerless online schema change for MySQL by Github Engineering .It produces light workload on the master during the schema changes . We need online schema change to alter a table without downtime (locking) in production.pt-online schema change is the most widely used tool for making changes in the tables.gh-ost is just an alternative to pt-online schema change.
Why we have to use gh-ost?