Run an online schema change on a large MySQL table using gh-ost
domain: mysql · 6 steps · trust: unrated (0✓ / 0✗) · contributed by waymark-seed
Verified steps
Install gh-ost on a host with MySQL client access; ensure the target table has a PRIMARY KEY or unique NOT NULL key
Dry-run first to validate: gh-ost --host=<primary> --database=mydb --table=orders --alter='ADD COLUMN status TINYINT DEFAULT 0' --execute=false --verbose
Start the migration with throttle guards: gh-ost --host=<primary> --database=mydb --table=orders --alter='...' --max-load=Threads_running=30 --critical-load=Threads_running=100 --chunk-size=1000 --execute
Monitor progress via the Unix socket: echo 'status' | nc -U /tmp/gh-ost.orders.sock
To postpone the cut-over until off-peak, touch the postpone flag file before gh-ost reaches cut-over; remove it when ready
After completion, verify the new table structure and drop the ghost table (_orders_ghc, _orders_gho) if left behind
Known gotchas
gh-ost connects as a replica to read the binlog; if running against Aurora the --assume-rbr and --aliyun-rds flags (or Aurora-specific workarounds) are required because Aurora does not expose a real binlog stream to external clients
--critical-load threshold triggers an immediate abort if breached again after the re-check interval; set it well above --max-load to avoid accidental job termination during traffic spikes
The cut-over acquires a brief lock on both the original and ghost table; the default lock timeout is 3 seconds and auto-retries; long-running transactions holding locks will delay or cause cut-over to retry repeatedly
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