Zero-Risk MySQL Index Cleanup (Invisible Index & EXPLAIN ANALYZE)

Supanote Core Team @supanote · 2 min read

plain (sql) 1 day ago · 47 lines · 4 views

Artifact

Verified Blueprint MySQL 8.4 LTS

Drop unused or redundant MySQL indexes safely without downtime using sys schema audits, ALTER INDEX INVISIBLE, and EXPLAIN ANALYZE.

✓ Detects redundant prefix indexes and zero-read write-amplifying indexes via MySQL sys views
✓ Hides candidate indexes metadata-instantly (ALTER INDEX INVISIBLE) so rollback takes 1 millisecond
✓ Validates real iterator execution times and row estimates with EXPLAIN ANALYZE before online DROP

Quick Fetch

-- Zero-Risk MySQL 8.4 / 9.x Unused Index Cleanup Workflow
-- Avoids multi-hour index rebuilds if a seemingly unused index is needed by a monthly job

-- Step 1: List Unused & Redundant Indexes (Ensure server uptime >= 7 days)
SELECT
    object_schema AS db_name,
    object_name   AS table_name,
    index_name,
    format('ALTER TABLE %I.%I ALTER INDEX %I INVISIBLE;', object_schema, object_name, index_name) AS step1_hide_sql
FROM sys.schema_unused_indexes
WHERE object_schema NOT IN ('mysql', 'sys', 'performance_schema');

SELECT
    table_schema,
    table_name,
    redundant_index_name,
    redundant_index_columns,
    dominant_index_name,
    dominant_index_columns,
    sql_drop_index
FROM sys.schema_redundant_indexes;

-- Step 2: Hide Candidate Index Instantly (Metadata-Only Operation, Zero Table Lock)
ALTER TABLE orders ALTER INDEX idx_orders_legacy_status INVISIBLE;

-- Step 3: Compare Execution Plans With vs Without the Invisible Index in Current Session
EXPLAIN ANALYZE
SELECT id, customer_id, total_cents
FROM orders
WHERE status = 'processing' AND created_at >= NOW() - INTERVAL 7 DAY
ORDER BY created_at DESC LIMIT 100;

-- Toggle visibility ON solely for this session to verify whether latency changes:
SET SESSION optimizer_switch = 'use_invisible_indexes=on';
EXPLAIN ANALYZE
SELECT id, customer_id, total_cents
FROM orders
WHERE status = 'processing' AND created_at >= NOW() - INTERVAL 7 DAY
ORDER BY created_at DESC LIMIT 100;
SET SESSION optimizer_switch = 'use_invisible_indexes=off';

-- Step 4A: Emergency Instant Rollback (If p99 latency regressed during soak window)
-- ALTER TABLE orders ALTER INDEX idx_orders_legacy_status VISIBLE;

-- Step 4B: Permanent Lock-Free Removal After Safe Soak Window
ALTER TABLE orders DROP INDEX idx_orders_legacy_status, ALGORITHM=INPLACE, LOCK=NONE;

1-- Zero-Risk MySQL 8.4 / 9.x Unused Index Cleanup Workflow

2-- Avoids multi-hour index rebuilds if a seemingly unused index is needed by a monthly job

4-- Step 1: List Unused & Redundant Indexes (Ensure server uptime >= 7 days)

5SELECT

6 object_schema AS db_name,

7 object_name AS table_name,

8 index_name,

9 format('ALTER TABLE %I.%I ALTER INDEX %I INVISIBLE;', object_schema, object_name, index_name) AS step1_hide_sql

10FROM sys.schema_unused_indexes

11WHERE object_schema NOT IN ('mysql', 'sys', 'performance_schema');

13SELECT

14 table_schema,

15 table_name,

16 redundant_index_name,

17 redundant_index_columns,

18 dominant_index_name,

19 dominant_index_columns,

20 sql_drop_index

21FROM sys.schema_redundant_indexes;

23-- Step 2: Hide Candidate Index Instantly (Metadata-Only Operation, Zero Table Lock)

24ALTER TABLE orders ALTER INDEX idx_orders_legacy_status INVISIBLE;

26-- Step 3: Compare Execution Plans With vs Without the Invisible Index in Current Session

27EXPLAIN ANALYZE

28SELECT id, customer_id, total_cents

29FROM orders

30WHERE status = 'processing' AND created_at >= NOW() - INTERVAL 7 DAY

31ORDER BY created_at DESC LIMIT 100;

33-- Toggle visibility ON solely for this session to verify whether latency changes:

34SET SESSION optimizer_switch = 'use_invisible_indexes=on';

35EXPLAIN ANALYZE

36SELECT id, customer_id, total_cents

37FROM orders

38WHERE status = 'processing' AND created_at >= NOW() - INTERVAL 7 DAY

39ORDER BY created_at DESC LIMIT 100;

40SET SESSION optimizer_switch = 'use_invisible_indexes=off';

42-- Step 4A: Emergency Instant Rollback (If p99 latency regressed during soak window)

43-- ALTER TABLE orders ALTER INDEX idx_orders_legacy_status VISIBLE;

45-- Step 4B: Permanent Lock-Free Removal After Safe Soak Window

46ALTER TABLE orders DROP INDEX idx_orders_legacy_status, ALGORITHM=INPLACE, LOCK=NONE;

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