If you are unfamiliar with what to monitor in MySQL, starting with looking at what popular Monitoring products monitor. For example, the following is the list of MySQL Cacti Plugin measurements.
Innodb Buffer Pool Activity
- Pages Created
- Pages Written
- Pages Read
Innodb Buffer Pool Pages
- Pool Size
- Database Pages
- Free Pages
- Modified Pages
Inoodb File I/O
- File Reads
- Files Writes
- Log Writes
- File Fsyncs
Innodb Pending I/O
- Aio Log Ios
- Aio Sync ios
- Buffer Pool Flushes
- Chkp Writes
- Ibuf Aio Reads
- Log Flushes
- Log Writes
- Normal Aio Reads
- Normal Aio Writes
Innodb Insert Buffer
- Inserts
- Merged
- Merges
Innodb Log
- Log Buffer Size
- Log Bytes Written
- Log Bytes Flushed
- Unflushed Log
Innodb Row Operations
- Rows Read
- Rows Deleted
- Rows Updated
- Rows Inserted
Innodb Semaphores
- Spin Rounds
- Spin Waits
- OS Waits
Innodb Transactions
- Innodb Transactions
- Current Transactions
- History List
- Read Views
MySQL Binary/Relay Logs
- Binlog Cache use
- Binlog Cache Disk Use
- Binary Log Space
- Relay Log Space
MySQL Command Counters
- Questions
- SELECT
- DELETE
- INSERT
- UPDATE
- REPLACE
- LOAD
- DELETE MULTI
- INSERT SELECT
- UPDATE MULTI
- REPLACE SELECT
MySQL Connections
- Max Connections
- Max Used Connections
- Aborted Clients
- Aborted Connects
- Threads Connected
- Connections
MySQL Files and Tables
- Table Cache
- Open Tables
- Open Files
- Opened Tables
MySQL Network Traffic
- Bytes Received
- Bytes Sent
MySQL Processlist
- State Closing Tables
- State Copying to Tmp Table
- State End
- State Freeing Items
- State Init
- State Locked
- State Login
- State Preparing
- State Reading From Net
- State Sending Data
- State Sorting Result
- State Statistics
- State Updating
- State Writing to Net
- State None
- State Other
MySQL Query Cache
- Queries In Cache
- Hits
- Inserts
- Not Cached
- Lowmem Prunes
MySQL Query Cache Memory
- Query Cache Size
- Free Memory
- Total Blocks
- Free Blocks
MySQL Replication
- Slave Running
- Slave Stopped
- Slave Lag
- Slave Open Temp Tables
- Slave Retried Transactions
MySQL Select Types
- Select Full Join
- Select Full Range Join
- Select Range
- Select Range Check
- Select Scan
MySQL Sorts
- Sort Rows
- Sort Range
- Sort Merge Passes
- Sort Scan
MySQL Table Locks
- Table Locks Immediate
- Table Locks Waited
- Slow Queries
MySQL Temporary Objects
- Created Tmp Tables
- Created Tmp Disk Tables
- Created Tmp Files
MySQL Threads
- Thread Cache Size
- Threads Created