Pt-online-schema-change slow down


I started pt-online-schema-change(pt-OSC) for one of my table which is 265Gb in size in Aurora-mysql.Its very critical and highly accessed table.We are converting the column datatype from INT to BIGINT.The pt-OSC ran good for 15 hours and suddenly its performance degraded and started copying rows very slowly…Initially it was copying 80-90 million rows in one hour but suddenly its performance dropped and it now copying 5-6 million per hour…I checked CPU and memory and they look fine.As this is production environment , I had to pause the job for few hours whenever there is a high traffic.Initally when I resumed the job after 1-2 hours few times, it was working fine but later I resumed the job after almost 12 hours and pt-OSC was very slow…It copied only 60 million rows in 11 hours.Here is our pt-OSC command

pt-online-schema-change --recursion-method=none --chunk-size=5000 --max-load Threads_running=150 --critical-load Threads_running=300 --alter-foreign-keys-method=auto --alter=“MODIFY BIGINT NOT NULL AUTO_INCREMENT DEFAULT NULL” h="${HOST}",P=3306,u=${USER},p="${PASSWORD}",D=,t= --charset=utf8mb4 --print --pause-file /tmp/pause-file --execute

Its still running but very slow…Any help would be greatly appreciated.

Did you check disk usage/iops? Check the history length of InnoDB. Is it growing?