O & M troubleshooting - use hcache plug-in to troubleshoot excessive buffer/cache occupancy

One hcache plug-in unit

1.1 hcache What plug-ins do

hcache Is based on pcstat Of ,pcstat You can check whether a file is cached and according to the process pid To see which files are cached .hcache On the basis of it, we add View the entire operating system Cache And according to the use Cache Characteristics of size sorting .

1.2 buffer and cache Cause of occurrence  

1. When your service process When reading and writing files ,Linux The kernel is for Improve the reading and writing speed of the service , The file will be placed here buffer/cache  For caching , because  Linux Characteristics of service That is, everything will exist in the form of documents , So you will find that whether or not you have done large-scale reading and writing to the file , Mechanical buffer/cache  It always exists , And keep increasing , This is because the network connection generated by the server is good , User agreement （UDP） Socket, too , The data system in this part will create corresponding file descriptors for the application , And these documents Use of descriptors , Will re-enter buffer/cache  For reading and writing , So this is also your machine will always exist higher buffer/cache  Why .

2.  When the service memory is sufficient ,Linux In order to speed up the efficiency of reading and writing files, the kernel will put the files into buffer/cache  in To ensure reading and writing efficiency , But in fact , Just do it After your application finishes reading and writing files ,buffer/cache  This part of memory will not be released automatically , It is reserved as a buffer , Wait until your service process reads and writes the same file the next time , All operations of re initializing the memory are omitted ; So this will lead to , When your application process frequently reads and writes to different files , You will find that the service can be used directly free An important reason why memory will be less and less ; Don't buffer/cache  In this endless cache, it will not be automatically released ？ Of course not. , When the server is under high memory pressure , The memory will be recycled automatically , As free Space is allocated to other processes , The main one of them is the memory recycled , It is buffer/cache  Buffer memory block for ;

1.3 Manual recycling mechanism

In addition to reclaiming memory when the system process memory is under great pressure , We can also do it manually buffer/cache Recycling , But because of buffer/cache It is mainly used for reading and writing files , So when you recycle files , Usually associated with a system IO Puma is high , Because the system kernel is also compared cache Whether the data in is consistent with the data in the hard disk , If there are inconsistencies, you need to write , Then the memory can be recycled ;