Introduction The InnoDB buffer pool caches data and indexes in memory for fast access. Resizing it during production—whether to increase capacity or reduce memory usage—can cause performance degradation as pages are loaded, evicted, and reorganized. Without proper tuning, the resize operation can cause minutes of elevated latency.

Symptoms - Query latency spikes during and after buffer pool resize - `SHOW ENGINE INNODB STATUS` shows `BUF POOL` section with pages being loaded - Buffer pool hit rate drops from 99.9% to below 90% - `Innodb_buffer_pool_read_requests` vs `Innodb_buffer_pool_reads` ratio worsens - Application timeout errors correlating with resize operation

Common Causes - Resizing buffer pool without configuring `innodb_buffer_pool_chunk_size` - Increasing buffer pool by a non-multiple of the chunk size - Resizing during peak traffic hours - Not warming up the buffer pool after resize - Reducing buffer pool size below the working set size

Step-by-Step Fix 1. **Check current buffer pool configuration": ```sql SHOW VARIABLES LIKE 'innodb_buffer_pool%'; -- Key values: -- innodb_buffer_pool_size -- innodb_buffer_pool_chunk_size -- innodb_buffer_pool_instances ```

  1. 1.**Calculate the correct new size":
  2. 2.```sql
  3. 3.-- New size should be a multiple of chunk_size * instances
  4. 4.SELECT
  5. 5.@@innodb_buffer_pool_chunk_size AS chunk_size,
  6. 6.@@innodb_buffer_pool_instances AS instances,
  7. 7.@@innodb_buffer_pool_chunk_size * @@innodb_buffer_pool_instances AS chunk_total,
  8. 8.@@innodb_buffer_pool_size AS current_size,
  9. 9.ROUND(@@innodb_buffer_pool_size * 1.5 / (@@innodb_buffer_pool_chunk_size * @@innodb_buffer_pool_instances)) *
  10. 10.(@@innodb_buffer_pool_chunk_size * @@innodb_buffer_pool_instances) AS recommended_new_size;
  11. 11.`
  12. 12.**Resize the buffer pool online":
  13. 13.```sql
  14. 14.-- Resize to 24GB (must be multiple of chunk_size * instances)
  15. 15.SET GLOBAL innodb_buffer_pool_size = 25769803776;

-- Monitor the resize progress SELECT event_name, SUM(CURRENT_NUMBER_OF_BYTES_USED) AS bytes_used FROM performance_schema.memory_summary_global_by_event_name WHERE event_name LIKE 'memory/innodb/buf_buf_pool' GROUP BY event_name; ```

  1. 1.**Monitor buffer pool warmup after resize":
  2. 2.```sql
  3. 3.-- Check buffer pool hit rate
  4. 4.SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool_read%';

-- Calculate hit rate SELECT ROUND( (1 - VARIABLE_VALUE / ( SELECT VARIABLE_VALUE FROM information_schema.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_buffer_pool_read_requests' )) * 100, 2 ) AS miss_rate_pct FROM information_schema.GLOBAL_STATUS WHERE VARIABLE_NAME = 'Innodb_buffer_pool_reads'; ```

  1. 1.**Enable buffer pool dump/load for faster warmup":
  2. 2.```sql
  3. 3.SET GLOBAL innodb_buffer_pool_dump_at_shutdown = ON;
  4. 4.SET GLOBAL innodb_buffer_pool_load_at_startup = ON;

-- Manually trigger dump before maintenance SET GLOBAL innodb_buffer_pool_dump_now = ON;

-- Manually trigger load after restart SET GLOBAL innodb_buffer_pool_load_now = ON;

-- Monitor load progress SELECT * FROM information_schema.INNODB_BUFFER_POOL_LOAD_STATUS; ```

Prevention - Size the buffer pool correctly from the start (typically 70-80% of RAM) - Use buffer pool dump/load to minimize warmup time after restarts - Resize in increments of `innodb_buffer_pool_chunk_size * innodb_buffer_pool_instances` - Perform resize during low-traffic periods when possible - Monitor buffer pool hit rate before and after resize to verify improvement - Set `innodb_buffer_pool_dump_pct = 75` to save 75% of warm pages at shutdown - Avoid reducing buffer pool below the current working set size