All user operations (delete, insert, update) are logged in the tuple log and executed. There tuple log may fill up because:
Execution slows due to CPU or disk I/O contention
The mirror node is slow in receiving the log records, which can happen as a result of:
Network contention, so the log records do not reach the mirror node
CPU and disk contention at the mirror node, which keeps it from processing the received log records quickly enough (“log throw due to...” messages in the history files).
If the tuple log is out of space, the history files contain messages showing HIGH LOAD on the tuple log.
Check CPU usage, as described in Improving CPU Utilization
If CPU utilization is not a problem, check the disk I/O. If the disk shows contention, avoid page faults when log records are being processed by increasing the data buffer size with hadbm set DataBufferPoolSize=... If there is disk contention, follow the solutions suggested in Is There Disk Contention?
Look for evidence of network contention, and resolve bottlenecks.
Increase the tuple log buffer using hadbm set LogBufferSize=...