RedHat6(CentOS6) warning - transparent hugepage support

[former_SQLA_member1694890]

We are using in our product - SA 12.0.1.3873 on Linux (RedHat, CentOS). Recently move from OS version 5.8 to OS version 6.4. During DB start appears follow warning -

I. 10/10 10:53:40. Running Linux 2.6.32-358.el6.x86_64 #1 SMP Fri Feb 22 00:31:26 UTC 2013 on X86_64 I. 10/10 10:53:40. Server built for X86_64 processor architecture W. 10/10 10:53:40. Direct IO disabled for file '/opt/sybase/data/db/cfg/allot_cfg.db' because transparent hugepage support is enabled and madvise is not supported

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?

Thanks, HBrener

[MarkCulp]

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.