Too many open files solution

The test environment appeared after running for a period of time too many open files, Lead to a regular report redis Tasks of frequently fail .

linux The default is 1024, It can be done by ulimit -n Command quantity adjustment .
example ：ulimit -n 4096
Not root Users can only set it to 4096, If you need more, you need root jurisdiction .

（ Specific modification method link :Linux TCP The connection limit configuration appears open too many open files_Clovemeo The blog of -CSDN Blog During interface testing , When the number of users exceeds 400 after , Will appear socket connection reset, Obviously, the system cannot create a connection , View the system created at this time TCP Connect ,netstat -ant |grepESTABLISHED |wc -l, Approximate quantity 1000 many .ulimit -n The default view system is 1024 The modification limits are as follows ： First step , modify /etc/security/limits.conf file , Add the following line to the file (* Refers to the system user name ), modify Linux The system's soft and hard restrictions on the number of open files ：so.https://blog.csdn.net/Clovemeo/article/details/124954657?spm=1001.2014.3001.5501）

1. Carry out orders ps -ef | grep java, Find out the process id：13945.

   

    

    

2. perform lsof -p 13945

   

   It is found that a large number of file handles have not been released . It is suspected that the small partner in the group did not traverse the file close Lead to .
   So look for clues from the code .

    

   

   The reason for the discovery is delete The method uses DirectoryStream did not close.
   java8 Inside Files.newDirectoryStream(p), It's usually used

   try(Files.newDirectoryStream()){
   } catch() {
   }
   

   The way , To avoid explicit close Release resources .
   So judge the classmate who wrote this code at that time Files.newDirectoryStream() Example time , I can't see close() Method mistakenly thinks that you don't need to release files to use directly . Led to too many open files It's abnormal .

   Another thing to note , stay try() File opened in , Do not delete , Otherwise, the handle cannot be released . for example ：

   try(InputStream inputStream = new FileInputStream(new File(path))) {
       // doSomething();
   } catch(Exception e) {
   }finally{
       Files.deleteIfExists(Paths.get(path));
   }
   

   It will lead to the following results ：

   

   File handle not released

   summary ：
   encounter too many open files when ,

3. perform lsof -p <pid>, View the handle opened by the process
   If the number of handles is abnormal , Then check the cause of abnormality according to the open handle , If the handle is normal , Then proceed to the second step as follows .

4. perform unlimit -a, see open files( The maximum number of files allowed to be opened )