percona-online-schema-change is taking a lot of time

We have a table with 600M+ records and using AWS Aurora with master-slave replication. **Requirement:** We need to add two columns with index in customer table. **Aurora Instance Specs:** Ram: 30.5 GB CPU: 4 vCPU I replicated the cluster and created instance with same configuration and ran the update process to newly created master instance to see how it works. But it's taking a lot time; ( already been 4 days ) and still running. Is there anything I can do to speedup the alter process? **Command:** pt-online-schema-change --execute --ask-pass --user=admin --statistics --chunk-time=1 --alter 'ADD COLUMN email_sha1 CHAR(40) DEFAULT null, ADD COLUMN email_sha256 CHAR(64) DEFAULT null, ADD INDEX email_sha1(email_sha1) USING BTREE, ADD INDEX email_sha256(email_sha256) USING BTREE' D=example,t=customer,h=example.public.rds.amazonaws.com