What causes MySQL high IOWait

There’s no single reason for I/O bottle necks. It can range from hardware issues to unoptimized server configurations. Here are the top issues.

1. Slow disk or degraded RAID array

Since disk access takes more time and is slower than accessing the memory, write and read operations slows up the MySQL performance., especially if the disk is slow. I/O wait can increase if the disk is degraded or corrupted.

2. Low system memory

As MySQL perform its transactions in the RAM, fetching the data each time between the RAM and the disk. If the RAM size is less, this can lead to many I/O wait cycles when dealing with large databases.

3. High number of transactions and size of data

The I/O overhead can further increase depending on the size of the database and number of transactions. Moreover, a lot of time is wasted especially during insert operations in large data sets, as write operations are slower than reads.

4. Unoptimized MySQL configuration

No write cache to store frequently accessed data sets, improper flushing mechanism, inadequate temporary table size for doing database operations, etc. are some issues that can lead to high I/O.

5. Complex queries

When the code in the application involves operations such as complex joins and quering over a large range in large data sets, the memory usage increases and so does the I/O overhead involved.