{"id":"2b4419bf-78c0-497b-a562-9d28d321537e","task":"Configure online schema changes with pt-online-schema-change (pt-osc) on MySQL","domain":"mysql","steps":["Install Percona Toolkit; verify the target table has a PRIMARY KEY (pt-osc requires it) with SHOW CREATE TABLE mydb.orders","Run a dry-run to inspect the generated plan: pt-online-schema-change --host=<primary> --user=dba --ask-pass --alter='ADD COLUMN status TINYINT NOT NULL DEFAULT 0' D=mydb,t=orders --dry-run","Execute the schema change with load guards: pt-online-schema-change --host=<primary> --user=dba --ask-pass --alter='...' D=mydb,t=orders --max-load=Threads_running=50 --critical-load=Threads_running=200 --chunk-size=1000 --execute","pt-osc creates a shadow table, copies rows in chunks using triggers on the original table to capture concurrent DML, then swaps tables at the end with a brief RENAME","Monitor progress via the printed output; pt-osc prints chunk progress and estimated time remaining; interrupt safely with Ctrl-C — it will clean up the shadow table","After completion, drop the old table (_orders_old) that pt-osc renames and retains by default, once you have verified the new table is correct"],"gotchas":["pt-osc uses DML triggers to keep the shadow table in sync; on very write-heavy tables, trigger overhead can noticeably increase replication lag and primary CPU — monitor replication closely during the migration","If the table already has triggers, pt-osc will refuse to run by default; use --alter-foreign-keys-method=auto and verify trigger compatibility, or prefer gh-ost which is triggerless","The final RENAME requires a brief metadata lock; long-running transactions at cut-over time will stall the rename — consider scheduling the cut-over during low-traffic windows and using --tries to configure retry behavior"],"contributor":"waymark-seed","created":"2026-06-12T08:27:56.245Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":{"status":"sampled","method":"legacy-file-sample","at":"2026-06-13T18:43:22.768Z"},"url":"https://mcp.waymark.network/r/2b4419bf-78c0-497b-a562-9d28d321537e"}