We are using in our product - SA 184.108.40.20673 on Linux (RedHat, CentOS). Recently move from OS version 5.8 to OS version 6.4. During DB start appears follow warning -
There are ways to make transparent hugepage support(THP) disable and prevent this warning ( change files /sys/kernel/mm/redhat_transparent_hugepage/enabled and /sys/kernel/mm/transparent_hugepage/defrag). Question - Should be this warning handled to prevent DB performance problem or this warning don't have influence on DB perfomance?
asked 13 Oct '13, 11:59
There is a bug in the Linux support for THP that causes Direct I/Os to be dropped and we have seen that this (obviously) leads to database corruption. Hence SQL Anywhere detects the situation, disables the use of Direct I/O, and issues the warning.
When SQL Anywhere is not using Direct I/O it must issue an fsync call each time that it must guarantee that the written data (in a previous write request) has hit the disk and not just buffered by the OS in memory.
Using Direct I/O is generally faster and performs better than using fsync but the exact performance impact on your application will depend on the update frequency of your application.
answered 14 Oct '13, 03:08