Transparent Huge Pages对数据库的影响
Transparent Huge Pages（THP)，本来是Linux为提高系统性能而做的努力，结果反而成了性能的隐患。一些主流数据库在官方文档都建议禁用该功能。
一、Greenplum Database(GPDB)
Disable Transparent Huge Pages (THP) as it degrades Greenplum Database performance.
引自：GPDB 6.12 文档
二、Oracle
Recently, in RHEL 6, Oracle Linux 6, and SUSE Linux Enterprise Server 11 a new feature, transparent HugePages was introduced. Transparent HugePages is an attempt to make the use of HugePages automatic and dynamic. Unfortunately the use of transparent HugePages in conjunction with the use of traditional HugePages is currently causing problems that can result in performance issues and system reboots. In My Oracle Support note 1557478.1, Oracle recommends not using transparent HugePages in conjunction with Oracle databases.
Note: In Oracle Linux version 6.5 Transparent HugePages have been removed.
根据MOS ID 1557478.1的说明。
Transparent HugePages are known to cause unexpected node reboots and performance problems with RAC, Oracle strongly advises to disable the use of Transparent HugePages. In addition, Transparent Hugepages may cause problems even in a single-instance database environment with unexpected performance problems or delays. As such, Oracle recommends disabling Transparent HugePages on all Database servers running Oracle.
三、MongoDB
Transparent Huge Pages (THP) is a Linux memory management system that reduces the overhead of Translation Lookaside Buffer (TLB) lookups on machines with large amounts of memory by using larger memory pages.
However, database workloads often perform poorly with THP enabled, because they tend to have sparse rather than contiguous memory access patterns. When running MongoDB on Linux, THP should be disabled for best performance.
引自：MongoDB文档
四、问题
- 以上提及的几乎都是RHEL 6版本。Linux 内核 4.* 关于THP有多次优化，新内核是否有改善？
- Orcale提到的“节点重启（that can result in performance issues and system reboots）”具体指什么问题？
五、参考
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