【MYSQL】mysql5.7-bug -information_schema的表被查询可能导致内存泄漏

1. [11 May 2017 6:57] Cho-Shing Ma
   
2. Description:
   
3. Running a query (on Information _Schema.tables (where clause) to exclude system schema, showing memory growing eventually Out-of-memory. Number of table entries around 20,000 (40 databases with 500 tables for each db)
   
4. 
   
5. mysql -uroot -h227.0.0.1 -e "select concat_ws('|',ifnull(TABLE_SCHEMA,''),ifnull(TABLE_NAME,''),ifnull(ENGINE,''),ifnull(TABLE_ROWS,'0'),ifnull(DATA_LENGTH,'0'), ifnull(INDEX_LENGTH,'0'),ifnull(DATA_FREE,'0'), ifnull(TABLE_COLLATION,''),ifnull(CREATE_TIME,''), ifnull(UPDATE_TIME,'')) from information_schema.TABLES where TABLE_SCHEMA not in ('mysql','test','information_schema','performance_schema','sys');"
   
6. 
   
7. How to repeat:
   
8. Please refer to attached document.
   
9. 
   
10. table_definition_cache=10000
    
11. table_open_cache =10000
    
12. innodb_open_files=10000
    
13. open_files_limit=10000
    
14. 
    
15. run the sql query every second and record the memory growing from OS and the mysqld.
    
16. 
    
17. mysql -uroot -h227.0.0.1 -e "select concat_ws('|',ifnull(TABLE_SCHEMA,''),ifnull(TABLE_NAME,''),ifnull(ENGINE,''),ifnull(TABLE_ROWS,'0'),ifnull(DATA_LENGTH,'0'), ifnull(INDEX_LENGTH,'0'),ifnull(DATA_FREE,'0'), ifnull(TABLE_COLLATION,''),ifnull(CREATE_TIME,''), ifnull(UPDATE_TIME,'')) from information_schema.TABLES where TABLE_SCHEMA not in ('mysql','test','information_schema','performance_schema','sys');"
    
18. 
    
19. Suggested fix:
    
20. No idea but the memory is growing.

日前，作者遇到一个疑似"内存"泄露的问题，一时找不头绪，然后就从mysql的官方上找线索，发现了上面的bug（见上图，bug id 86279 ),查询information_schema下的tables表导致内存溢出。 经动手简单测试，貌似还真有这回事。 同理，该schema下的其他的一下表，可能也存在这个问题。

对于表数量特别多的系统，可能更需要慎重。 但也无须惊慌，上面写的重现现象是重复查询，然后内存逐步增长，最终OOM.

以上信息仅供各位朋友参考！！！



percona 5.7

1. https://bugs.launchpad.net/percona-server/+bug/1693511 --performance占用大量内存--10G左右稳定下来